mongodb tdg chap2 4 sampler

7/29/2019 MongoDB TDG Chap2 4 Sampler

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MongoDB: The Definitive GuideE\.ULVWLQD&KRGRURZDQG0LFKDHO'LUROI

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Table of Contents

Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi

Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1$5LFK'DWD0RGHO (DV\6FDOLQJ 7RQVRI)HDWXUHV :LWKRXW6DFULILFLQJ6SHHG 6LPSOH$GPLQLVWUDWLRQ %XW:DLW7KDWV1RW$OO

2. Getting Started . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5'RFXPHQWV

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3. Creating, Updating, and Deleting Documents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23,QVHUWLQJDQG6DYLQJ'RFXPHQWV

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4. Querying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45,QWURGXFWLRQWRILQG

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5. Indexing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65,QWURGXFWLRQWR,QGH[LQJ

6FDOLQJ,QGH[HV ,QGH[LQJ.H\VLQ(PEHGGHG'RFXPHQWV

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7. Advanced Topics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93'DWDEDVH&RPPDQGV

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8. Administration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1116WDUWLQJDQG6WRSSLQJ0RQJR'%

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9. Replication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1270DVWHU6ODYH5HSOLFDWLRQ

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10. Sharding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143,QWURGXFWLRQWR6KDUGLQJ $XWRVKDUGLQJLQ0RQJR'%

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11. Example Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155&KHPLFDO6HDUFK(QJLQH-DYD

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A. Installing MongoDB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173

B. mongo: The Shell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177

C. MongoDB Internals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183

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CHAPTER 2

Getting Started

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6 | Chapter 2:Getting Started


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DGPLQ7KLVLVWKHURRWGDWDEDVHLQWHUPVRIDXWKHQWLFDWLRQ,IDXVHULVDGGHGWRWKHDGPLQ GDWDEDVH WKH XVHU DXWRPDWLFDOO\ LQKHULWV SHUPLVVLRQV IRU DOO GDWDEDVHV7KHUHDUHDOVRFHUWDLQVHUYHUZLGHFRPPDQGVWKDWFDQEHUXQRQO\IURPWKH DGPLQGDWDEDVHVXFKDVOLVWLQJDOORIWKHGDWDEDVHVRUVKXWWLQJGRZQWKHVHUYHU

ORFDO7KLVGDWDEDVHZLOOQHYHUEHUHSOLFDWHGDQGFDQEHXVHGWRVWRUHDQ\FROOHFWLRQVWKDWVKRXOGEHORFDOWRDVLQJOHVHUYHUVHH&KDSWHUIRUPRUHLQIRUPDWLRQDERXWUHSOLFDWLRQDQGWKHORFDOGDWDEDVH

FRQILJ:KHQ0RQJRLVEHLQJXVHGLQDVKDUGHGVHWXSVHH&KDSWHUWKHFRQILJGDWDEDVHLVXVHGLQWHUQDOO\WRVWRUHLQIRUPDWLRQDERXWWKHVKDUGV

%\SUHSHQGLQJDFROOHFWLRQVQDPHZLWKLWVFRQWDLQLQJGDWDEDVH\RXFDQJHWDIXOO\TXDOLILHG FROOHFWLRQ QDPH FDOOHG D QDPHVSDFH )RU LQVWDQFH LI \RX DUH XVLQJ WKHEORJSRVWVFROOHFWLRQLQWKHFPVGDWDEDVHWKHQDPHVSDFHRIWKDWFROOHFWLRQZRXOGEHcms.blog.posts1DPHVSDFHVDUHOLPLWHGWRE\WHVLQOHQJWKDQGLQSUDFWLFHVKRXOGEHOHVVWKDQE\WHVORQJ)RUPRUHRQQDPHVSDFHVDQGWKHLQWHUQDOUHSUHVHQWDWLRQ

RIFROOHFWLRQVLQ0RQJR'%VHH$SSHQGL[&

Databases | 9


15/48

Getting and Starting MongoDB0RQJR'%LVDOPRVWDOZD\VUXQDVD QHWZRUNVHUYHUWKDWFOLHQWVFDQFRQQHFWWRDQGSHUIRUPRSHUDWLRQVRQ7RVWDUWWKHVHUYHUUXQWKHmongodH[HFXWDEOH

$ ./mongod

./mongod --help for help and startup optionsSun Mar 28 12:31:20 Mongo DB : starting : pid = 44978 port = 27017dbpath = /data/db/ master = 0 slave = 0 64-bitSun Mar 28 12:31:20 db version v1.5.0-pre-, pdfile version 4.5Sun Mar 28 12:31:20 git version: ...Sun Mar 28 12:31:20 sys info: ...Sun Mar 28 12:31:20 waiting for connections on port 27017Sun Mar 28 12:31:20 web admin interface listening on port 28017

2ULI\RXUHRQ:LQGRZVUXQWKLV

$ mongod.exe

)RUGHWDLOHGLQIRUPDWLRQRQLQVWDOOLQJ0RQJR'%RQ\RXUV\VWHPVHH$SSHQGL[$

:KHQUXQZLWKQRDUJXPHQWVmongodZLOOXVHWKHGHIDXOWGDWDGLUHFWRU\GDWDGERU&?GDWD?GE?RQ:LQGRZVDQGSRUW,IWKHGDWDGLUHFWRU\GRHVQRWDOUHDG\H[LVWRULVQRWZULWDEOHWKHVHUYHUZLOOIDLOWRVWDUW,WLVLPSRUWDQWWRFUHDWHWKHGDWDGLUHFWRU\HJPNGLUSGDWDGEDQGWRPDNHVXUH\RXUXVHUKDVSHUPLVVLRQWRZULWHWRWKHGLUHFWRU\EHIRUHVWDUWLQJ0RQJR'%7KHVHUYHUZLOODOVRIDLOWRVWDUWLIWKHSRUWLVQRWDYDLODEOHWKLVLVRIWHQFDXVHGE\DQRWKHULQVWDQFHRI0RQJR'%WKDWLVDOUHDG\UXQQLQJ

7KHVHUYHUZLOOSULQWVRPHYHUVLRQDQGV\VWHPLQIRUPDWLRQDQGWKHQEHJLQZDLWLQJIRUFRQQHFWLRQV%\GHIDXOW0RQJR'%OLVWHQVIRUVRFNHWFRQQHFWLRQVRQSRUW

mongodDOVRVHWVXSDYHU\EDVLF+773VHUYHUWKDWOLVWHQVRQDSRUWKLJKHUWKDQWKHPDLQSRUWLQWKLVFDVH7KLVPHDQVWKDW\RXFDQJHWVRPHDGPLQLVWUDWLYHLQIRUPDWLRQDERXW\RXUGDWDEDVHE\RSHQLQJDZHEEURZVHUDQGJRLQJWRKWWSORFDOKRVW


16/48

MongoDB Shell0RQJR'%FRPHVZLWKD-DYD6FULSWVKHOOWKDWDOORZVLQWHUDFWLRQZLWKD0RQJR'%LQVWDQFHIURPWKHFRPPDQGOLQH7KHVKHOOLVYHU\XVHIXOIRUSHUIRUPLQJDGPLQLVWUDWLYHIXQFWLRQVLQVSHFWLQJDUXQQLQJLQVWDQFHRUMXVWSOD\LQJDURXQG7KHmongoVKHOOLVD

FUXFLDOWRROIRUXVLQJ0RQJR'%DQGLVXVHGH[WHQVLYHO\WKURXJKRXWWKHUHVWRIWKHWH[W

Running the Shell7RVWDUWWKHVKHOOUXQWKHmongoH[HFXWDEOH

$ ./mongoMongoDB shell version: 1.6.0url: testconnecting to: testtype "help" for help>

7KHVKHOODXWRPDWLFDOO\DWWHPSWVWRFRQQHFWWRD0RQJR'%VHUYHURQVWDUWXSVRPDNHVXUH\RXVWDUWmongodEHIRUHVWDUWLQJWKHVKHOO

7KHVKHOOLVDIXOOIHDWXUHG-DYD6FULSWLQWHUSUHWHUFDSDEOHRIUXQQLQJDUELWUDU\-DYD6FULSWSURJUDPV7RLOOXVWUDWHWKLVOHWVSHUIRUPVRPHEDVLFPDWK

> x = 200200> x / 5;40

:HFDQDOVROHYHUDJHDOORIWKHVWDQGDUG-DYD6FULSWOLEUDULHV

> Math.sin(Math.PI / 2);

1> new Date("2010/1/1");"Fri Jan 01 2010 00:00:00 GMT-0500 (EST)"> "Hello, World!".replace("World", "MongoDB");Hello, MongoDB!

:HFDQHYHQGHILQHDQGFDOO-DYD6FULSWIXQFWLRQV

> function factorial (n) {... if (n factorial(5);120

1RWHWKDW\RXFDQFUHDWHPXOWLOLQHFRPPDQGV7KHVKHOOZLOOGHWHFWZKHWKHUWKH-DYD6FULSWVWDWHPHQWLVFRPSOHWHZKHQ\RXSUHVV(QWHUDQGLILWLVQRWZLOODOORZ\RXWRFRQWLQXHZULWLQJLWRQWKHQH[WOLQH

MongoDB Shell | 11


17/48

A MongoDB Client$OWKRXJKWKHDELOLW\WRH[HFXWHDUELWUDU\-DYD6FULSWLVFRROWKHUHDOSRZHURIWKHVKHOOOLHVLQWKHIDFWWKDWLWLVDOVRDVWDQGDORQH0RQJR'%FOLHQW2QVWDUWXSWKHVKHOOFRQQHFWVWRWKHWHVWGDWDEDVHRQD0RQJR'%VHUYHUDQGDVVLJQVWKLVGDWDEDVHFRQQHFWLRQWRWKHJOREDOYDULDEOHdb7KLVYDULDEOHLVWKHSULPDU\DFFHVVSRLQWWR0RQJR'%WKURXJKWKHVKHOO

7KHVKHOOFRQWDLQVVRPHDGGRQVWKDWDUHQRWYDOLG-DYD6FULSWV\QWD[EXWZHUHLPSOHPHQWHGEHFDXVHRIWKHLUIDPLOLDULW\WRXVHUVRI64/VKHOOV7KHDGGRQVGRQRWSURYLGHDQ\H[WUDIXQFWLRQDOLW\EXWWKH\DUHQLFHV\QWDFWLFVXJDU)RULQVWDQFHRQHRIWKHPRVWLPSRUWDQWRSHUDWLRQVLVVHOHFWLQJZKLFKGDWDEDVHWRXVH

> use foobarswitched to db foobar

1RZLI\RXORRNDWWKHdbYDULDEOH\RXFDQVHHWKDWLWUHIHUVWRWKHIRREDUGDWDEDVH

> db

foobar

%HFDXVHWKLVLVD-DYD6FULSWVKHOOW\SLQJDYDULDEOHZLOOFRQYHUWWKHYDULDEOHWRDVWULQJLQWKLVFDVHWKHGDWDEDVHQDPHDQGSULQWLW

&ROOHFWLRQVFDQEHDFFHVVHGIURPWKHdbYDULDEOH)RUH[DPSOHdb.bazUHWXUQVWKHED]FROOHFWLRQLQWKHFXUUHQWGDWDEDVH1RZWKDWZHFDQDFFHVVDFROOHFWLRQLQWKHVKHOOZHFDQSHUIRUPDOPRVWDQ\GDWDEDVHRSHUDWLRQ

Basic Operations with the Shell:HFDQXVH WKH IRXU EDVLFRSHUDWLRQV FUHDWH UHDGXSGDWHDQG GHOHWH&58'WRPDQLSXODWHDQGYLHZGDWDLQWKHVKHOO

Create

7KHinsertIXQFWLRQDGGVDGRFXPHQWWRDFROOHFWLRQ)RUH[DPSOHVXSSRVHZHZDQWWRVWRUHDEORJSRVW)LUVWZHOOFUHDWHDORFDOYDULDEOHFDOOHGpostWKDWLVD-DYD6FULSWREMHFW UHSUHVHQWLQJ RXU GRFXPHQW ,W ZLOO KDYH WKH NH\V "title" "content" DQG"date"WKHGDWHWKDWLWZDVSXEOLVKHG

> post = {"title" : "My Blog Post",... "content" : "Here's my blog post.",... "date" : new Date()}{

"title" : "My Blog Post","content" : "Here's my blog post.","date" : "Sat Dec 12 2009 11:23:21 GMT-0500 (EST)"

}

7KLVREMHFWLVDYDOLG0RQJR'%GRFXPHQWVRZHFDQVDYHLWWRWKHEORJFROOHFWLRQXVLQJWKHinsertPHWKRG



18/48

> db.blog.insert(post)

7KHEORJSRVWKDVEHHQVDYHGWRWKHGDWDEDVH:HFDQVHHLWE\FDOOLQJfindRQWKHFROOHFWLRQ

> db.blog.find(){

"_id" : ObjectId("4b23c3ca7525f35f94b60a2d"),"title" : "My Blog Post","content" : "Here's my blog post.","date" : "Sat Dec 12 2009 11:23:21 GMT-0500 (EST)"

}

db.blog.findOne(){

"_id" : ObjectId("4b23c3ca7525f35f94b60a2d"),"title" : "My Blog Post","content" : "Here's my blog post.","date" : "Sat Dec 12 2009 11:23:21 GMT-0500 (EST)"

}

findDQGfindOneFDQDOVREHSDVVHGFULWHULDLQWKHIRUPRIDTXHU\GRFXPHQW7KLVZLOOUHVWULFWWKHGRFXPHQWVPDWFKHGE\WKHTXHU\7KHVKHOOZLOODXWRPDWLFDOO\GLVSOD\XS

WRGRFXPHQWVPDWFKLQJDfindEXWPRUHFDQEHIHWFKHG6HH &KDSWHUIRUPRUHLQIRUPDWLRQRQTXHU\LQJ

Update

,IZHZRXOGOLNHWRPRGLI\RXUSRVWZHFDQXVHupdateupdateWDNHVDWOHDVWWZRSDUDPHWHUVWKHILUVWLVWKHFULWHULDWRILQGZKLFKGRFXPHQWWRXSGDWHDQGWKHVHFRQGLVWKHQHZGRFXPHQW6XSSRVHZHGHFLGHWRHQDEOHFRPPHQWVRQWKHEORJSRVWZHFUHDWHGHDUOLHU:HOOQHHGWRDGGDQDUUD\RIFRPPHQWVDVWKHYDOXHIRUDQHZNH\LQRXUGRFXPHQW

7KHILUVWVWHSLVWRPRGLI\WKHYDULDEOHpostDQGDGGD"comments"NH\

> post.comments = [][ ]

7KHQZHSHUIRUPWKHXSGDWHUHSODFLQJWKHSRVWWLWOHG0\%ORJ3RVWZLWKRXUQHZYHUVLRQRIWKHGRFXPHQW

> db.blog.update({title : "My Blog Post"}, post)

MongoDB Shell | 13


19/48

1RZWKHGRFXPHQWKDVD"comments"NH\,IZHFDOOfindDJDLQZHFDQVHHWKHQHZNH\

> db.blog.find(){

"_id" : ObjectId("4b23c3ca7525f35f94b60a2d"),"title" : "My Blog Post","content" : "Here's my blog post.",

"date" : "Sat Dec 12 2009 11:23:21 GMT-0500 (EST)""comments" : [ ]}

Delete

removeGHOHWHVGRFXPHQWVSHUPDQHQWO\IURPWKHGDWDEDVH&DOOHGZLWKQRSDUDPHWHUVLWUHPRYHVDOO GRFXPHQWVIURPDFROOHFWLRQ,W FDQ DOVRWDNHDGRFXPHQWVSHFLI\LQJFULWHULDIRUUHPRYDO)RUH[DPSOHWKLVZRXOGUHPRYHWKHSRVWZHMXVWFUHDWHG

> db.blog.remove({title : "My Blog Post"})

1RZWKHFROOHFWLRQZLOOEHHPSW\DJDLQ

Tips for Using the Shell%HFDXVHmongoLVVLPSO\D-DYD6FULSWVKHOO\RXFDQJHWDJUHDWGHDORIKHOSIRULWE\VLPSO\ORRNLQJXS-DYD6FULSWGRFXPHQWDWLRQRQOLQH7KHVKHOODOVRLQFOXGHVEXLOWLQKHOSWKDWFDQEHDFFHVVHGE\W\SLQJhelp

> helpHELP

show dbs show database namesshow collections show collections in current databaseshow users show users in current database

show profile show recent system.profile entries w. time >= 1msuse set current database to db.help() help on DB methodsdb.foo.help() help on collection methodsdb.foo.find() list objects in collection foodb.foo.find( { a : 1 } ) list objects in foo where a == 1it result of the last line evaluated

+HOSIRUGDWDEDVHOHYHOFRPPDQGVLVSURYLGHGE\db.help();DQGKHOSDWWKHFROOHFWLRQVFDQEHDFFHVVHGZLWKdb.foo.help();

$JRRGZD\RIILJXULQJRXWZKDWDIXQFWLRQLVGRLQJLVWRW\SHLWZLWKRXWWKHSDUHQWKHVHV7KLVZLOOSULQWWKH-DYD6FULSWVRXUFHFRGHIRUWKHIXQFWLRQ)RUH[DPSOHLIZHDUHFXULRXV

DERXWKRZWKHupdateIXQFWLRQZRUNVRUFDQQRWUHPHPEHUWKHRUGHURISDUDPHWHUVZHFDQGRWKHIROORZLQJ

> db.foo.updatefunction (query, obj, upsert, multi) {

assert(query, "need a query");assert(obj, "need an object");this._validateObject(obj);this._mongo.update(this._fullName, query, obj,



20/48

upsert ? true : false, multi ? true : false);}

7KHUHLVDOVRDQDXWRJHQHUDWHG$3,RIDOOWKH-DYD6FULSWIXQFWLRQVSURYLGHGE\WKHVKHOODWKWWSDSLPRQJRGERUJMV

Inconvenient collection names)HWFKLQJDFROOHFWLRQZLWK db.collectionNameDOPRVWDOZD\VZRUNVXQOHVVWKHFROOHFWLRQQDPHDFWXDOO\LVDSURSHUW\RIWKHGDWDEDVHFODVV)RULQVWDQFHLIZHDUHWU\LQJWRDFFHVVWKHYHUVLRQFROOHFWLRQZHFDQQRWVD\db.versionEHFDXVHdb.versionLVDGDWDEDVHIXQFWLRQ,WUHWXUQVWKHYHUVLRQRIWKHUXQQLQJ0RQJR'%VHUYHU

> db.versionfunction () {

return this.serverBuildInfo().version;}

dbVFROOHFWLRQUHWXUQLQJEHKDYLRULVRQO\DIDOOEDFNIRUZKHQ-DYD6FULSWFDQQRWILQGD

PDWFKLQJSURSHUW\:KHQWKHUHLVDSURSHUW\ZLWKWKHVDPHQDPHDVWKHGHVLUHGFROOHFWLRQZHFDQXVHWKHgetCollectionIXQFWLRQ

> db.getCollection("version");test.version

7KLVFDQDOVREHKDQG\IRUFROOHFWLRQVZLWKLQYDOLG-DYD6FULSWLQWKHLUQDPHV)RUH[DPSOHIRREDULVDYDOLGFROOHFWLRQQDPHEXWLWVYDULDEOHVXEWUDFWLRQLQ-DYD6FULSW


21/48

Basic Data Types'RFXPHQWVLQ0RQJR'%FDQEHWKRXJKWRIDV-621OLNHLQWKDWWKH\DUHFRQFHSWXDOO\VLPLODUWRREMHFWVLQ-DYD6FULSW-621LVDVLPSOHUHSUHVHQWDWLRQRIGDWDWKHVSHFLILFDWLRQFDQEHGHVFULEHGLQDERXWRQHSDUDJUDSK KWWSZZZMVRQRUJSURYHVLWDQGOLVWVRQO\VL[GDWDW\SHV7KLVLVDJRRGWKLQJLQPDQ\ZD\VLWVHDV\WRXQGHUVWDQGSDUVHDQGUHPHPEHU2QWKHRWKHUKDQG-621VH[SUHVVLYHFDSDELOLWLHVDUHOLPLWHGEHFDXVHWKHRQO\W\SHVDUHQXOOERROHDQQXPHULFVWULQJDUUD\DQGREMHFW

$OWKRXJKWKHVHW\SHVDOORZIRUDQLPSUHVVLYHDPRXQWRIH[SUHVVLYLW\WKHUHDUHDFRXSOHRIDGGLWLRQDOW\SHVWKDWDUHFUXFLDOIRUPRVWDSSOLFDWLRQVHVSHFLDOO\ZKHQZRUNLQJZLWKDGDWDEDVH)RUH[DPSOH-621KDVQRGDWHW\SHZKLFKPDNHVZRUNLQJZLWKGDWHVHYHQPRUHDQQR\LQJWKDQLWXVXDOO\LV7KHUHLVDQXPEHUW\SHEXWRQO\RQHWKHUHLVQRZD\WRGLIIHUHQWLDWHIORDWVDQGLQWHJHUVQHYHUPLQGDQ\GLVWLQFWLRQEHWZHHQELWDQGELWQXPEHUV7KHUHLVQRZD\WRUHSUHVHQWRWKHUFRPPRQO\XVHGW\SHVHLWKHUVXFKDVUHJXODUH[SUHVVLRQVRUIXQFWLRQV

0RQJR'%DGGVVXSSRUWIRUDQXPEHURIDGGLWLRQDOGDWDW\SHVZKLOHNHHSLQJ-621VHVVHQWLDONH\YDOXHSDLUQDWXUH([DFWO\KRZYDOXHVRIHDFKW\SHDUHUHSUHVHQWHGYDULHVE\ODQJXDJHEXWWKLVLVDOLVWRIWKHFRPPRQO\VXSSRUWHGW\SHVDQGKRZWKH\DUHUHSUHVHQWHGDVSDUWRIDGRFXPHQWLQWKHVKHOO

QXOO1XOOFDQEHXVHGWRUHSUHVHQWERWKDQXOOYDOXHDQGDQRQH[LVWHQWILHOG

{"x" : null}

ERROHDQ7KHUHLVDERROHDQW\SHZKLFKZLOOEHXVHGIRUWKHYDOXHV'true'DQG'false'

{"x" : true}

ELWLQWHJHU7KLVFDQQRWEHUHSUHVHQWHGRQWKHVKHOO$VPHQWLRQHGHDUOLHU-DYD6FULSWVXSSRUWVRQO\ELWIORDWLQJSRLQWQXPEHUVVRELWLQWHJHUVZLOOEHFRQYHUWHGLQWRWKRVH

ELWLQWHJHU$JDLQWKHVKHOOFDQQRWUHSUHVHQWWKHVH7KHVKHOOZLOOGLVSOD\WKHPXVLQJDVSHFLDOHPEHGGHGGRFXPHQWVHHWKHVHFWLRQ1XPEHUVRQSDJHIRUGHWDLOV

ELWIORDWLQJSRLQWQXPEHU$OOQXPEHUVLQWKHVKHOOZLOOEHRIWKLVW\SH7KXVWKLVZLOOEHDIORDWLQJSRLQW

QXPEHU{"x" : 3.14}

$VZLOOWKLV

{"x" : 3}

VWULQJ$Q\VWULQJRI87)FKDUDFWHUVFDQEHUHSUHVHQWHGXVLQJWKHVWULQJW\SH

http://www.json.org/http://www.json.org/


22/48

{"x" : "foobar"}

V\PERO7KLVW\SHLVQRWVXSSRUWHGE\WKHVKHOO,IWKHVKHOOJHWVDV\PEROIURPWKHGDWDEDVHLWZLOOFRQYHUWLWLQWRDVWULQJ

REMHFWLG

$QREMHFWLGLVDXQLTXHE\WH,'IRUGRFXPHQWV6HHWKHVHFWLRQBLGDQG2EMHFW,GVRQSDJHIRUGHWDLOV

{"x" : ObjectId()}

GDWH'DWHVDUHVWRUHGDVPLOOLVHFRQGVVLQFHWKHHSRFK7KHWLPH]RQHLVQRWVWRUHG

{"x" : new Date()}

UHJXODUH[SUHVVLRQ'RFXPHQWVFDQFRQWDLQUHJXODUH[SUHVVLRQVXVLQJ-DYD6FULSWVUHJXODUH[SUHVVLRQV\QWD[

{"x" : /foobar/i}

FRGH'RFXPHQWVFDQDOVRFRQWDLQ-DYD6FULSWFRGH

{"x" : function() { /* ... */ }}

ELQDU\GDWD%LQDU\GDWDLVDVWULQJRIDUELWUDU\E\WHV,WFDQQRWEHPDQLSXODWHGIURPWKHVKHOO

PD[LPXPYDOXH%621FRQWDLQVDVSHFLDOW\SHUHSUHVHQWLQJWKHODUJHVWSRVVLEOHYDOXH7KHVKHOOGRHV

QRWKDYHDW\SHIRUWKLVPLQLPXPYDOXH

%621FRQWDLQVDVSHFLDOW\SHUHSUHVHQWLQJWKHVPDOOHVWSRVVLEOHYDOXH7KHVKHOOGRHVQRWKDYHDW\SHIRUWKLV

XQGHILQHG8QGHILQHGFDQEHXVHGLQGRFXPHQWVDVZHOO-DYD6FULSWKDVGLVWLQFWW\SHVIRUQXOODQGXQGHILQHG

{"x" : undefined}

DUUD\

6HWVRUOLVWVRIYDOXHVFDQEHUHSUHVHQWHGDVDUUD\V{"x" : ["a", "b", "c"]}

HPEHGGHGGRFXPHQW'RFXPHQWV FDQ FRQWDLQ HQWLUH GRFXPHQWV HPEHGGHG DV YDOXHV LQ D SDUHQWGRFXPHQW

{"x" : {"foo" : "bar"}}

Data Types | 17


23/48

Numbers-DYD6FULSWKDVRQHQXPEHUW\SH%HFDXVH0RQJR'%KDVWKUHHQXPEHUW\SHVE\WHLQWHJHUE\WHLQWHJHUDQGE\WHIORDWWKHVKHOOKDVWRKDFNDURXQG-DYD6FULSWVOLPLWDWLRQVDELW%\GHIDXOWDQ\QXPEHULQWKHVKHOOLVWUHDWHGDVDGRXEOHE\0RQJR'%7KLVPHDQVWKDWLI\RXUHWULHYHDE\WHLQWHJHUIURPWKHGDWDEDVHPDQLSXODWHLWVGRFXPHQWDQGVDYHLWEDFNWRWKHGDWDEDVH HYHQZLWKRXWFKDQJLQJWKHLQWHJHUWKHLQWHJHUZLOOEHUHVDYHGDVDIORDWLQJSRLQWQXPEHU7KXVLWLVJHQHUDOO\DJRRGLGHDQRWWRRYHUZULWHHQWLUHGRFXPHQWVIURPWKHVKHOOVHH&KDSWHUIRULQIRUPDWLRQRQPDNLQJFKDQJHVWRWKHYDOXHVRILQGLYLGXDONH\V

$QRWKHUSUREOHPZLWKHYHU\QXPEHUEHLQJUHSUHVHQWHGE\DGRXEOHLVWKDWWKHUHDUHVRPHE\WHLQWHJHUVWKDWFDQQRWEHDFFXUDWHO\UHSUHVHQWHGE\E\WHIORDWV7KHUHIRUHLI\RXVDYHDQE\WHLQWHJHUDQGORRNDWLWLQWKHVKHOOWKHVKHOOZLOOGLVSOD\LWDVDQHPEHGGHGGRFXPHQWLQGLFDWLQJWKDWLWPLJKWQRWEHH[DFW)RUH[DPSOHLIZHVDYHDGRFXPHQWZLWKD"myInteger"NH\ZKRVHYDOXHLVWKHELWLQWHJHU3DQGWKHQORRNDWLWLQWKHVKHOOLWZLOOORRNOLNHWKLV

> doc = db.nums.findOne(){

"_id" : ObjectId("4c0beecfd096a2580fe6fa08"),"myInteger" : {

"floatApprox" : 3}

}

7KHQXPEHULVQRWFKDQJHGLQWKHGDWDEDVHXQOHVV\RXPRGLI\DQGUHVDYHWKHREMHFWIURPWKHVKHOOLQZKLFKFDVHLWZLOOWXUQLQWRDIORDWWKHHPEHGGHGGRFXPHQWMXVWLQGLFDWHVWKDWWKHVKHOOLVGLVSOD\LQJDIORDWLQJSRLQWDSSUR[LPDWLRQRIDQE\WHLQWHJHU

,IWKLVHPEHGGHGGRFXPHQWKDVRQO\RQHNH\LWLVLQIDFWH[DFW,I\RXLQVHUWDQE\WHLQWHJHUWKDWFDQQRWEHDFFXUDWHO\GLVSOD\HGDVDGRXEOHWKHVKHOOZLOODGGWZRNH\V"top"DQG"bottom"FRQWDLQLQJWKHELWLQWHJHUVUHSUHVHQWLQJWKHKLJKRUGHUE\WHVDQGORZRUGHUE\WHVRIWKHLQWHJHUUHVSHFWLYHO\)RULQVWDQFHLIZHLQVHUW9223372036854775807WKHVKHOOZLOOVKRZXVWKHIROORZLQJ

> db.nums.findOne(){

"_id" : ObjectId("4c0beecfd096a2580fe6fa09"),"myInteger" : {

"floatApprox" : 9223372036854776000,"top" : 2147483647,

"bottom" : 4294967295}}

7KH"floatApprox"HPEHGGHGGRFXPHQWVDUHVSHFLDODQGFDQEHPDQLSXODWHGDVQXPEHUVDVZHOODVGRFXPHQWV

> doc.myInteger + 14



24/48

> doc.myInteger.floatApprox3

$OOE\WHLQWHJHUVFDQEHUHSUHVHQWHGH[DFWO\E\DQE\WHIORDWLQJSRLQWQXPEHUVRWKH\DUHGLVSOD\HGQRUPDOO\

Dates,Q-DYD6FULSWWKHDateREMHFWLVXVHGIRU0RQJR'%VGDWHW\SH:KHQFUHDWLQJDQHZDateREMHFWDOZD\VFDOOnew Date(...)QRWMXVWDate(...)&DOOLQJWKHFRQVWUXFWRUDVDIXQFWLRQWKDWLVQRWLQFOXGLQJnewUHWXUQVDVWULQJUHSUHVHQWDWLRQRIWKHGDWHQRWDQDFWXDODateREMHFW7KLVLVQRW0RQJR'%VFKRLFHLWLVKRZ-DYD6FULSWZRUNV,I\RXDUHQRWFDUHIXOWRDOZD\VXVHWKHDateFRQVWUXFWRU\RXFDQHQGXSZLWKDPLVKPDVKRIVWULQJVDQGGDWHV6WULQJVGRQRWPDWFKGDWHVDQGYLFHYHUVDVRWKLVFDQFDXVHSUREOHPVZLWKUHPRYLQJXSGDWLQJTXHU\LQJSUHWW\PXFKHYHU\WKLQJ

)RUDIXOOH[SODQDWLRQRI-DYD6FULSWV DateFODVVDQGDFFHSWDEOHIRUPDWVIRUWKHFRQ

VWUXFWRUVHH(&0$6FULSWVSHFLILFDWLRQVHFWLRQDYDLODEOHIRUGRZQORDGDW KWWSZZZHFPDVFULSWRUJ

'DWHVLQWKHVKHOODUHGLVSOD\HGXVLQJORFDOWLPH]RQHVHWWLQJV+RZHYHUGDWHVLQWKHGDWDEDVHDUHMXVWVWRUHGDVPLOOLVHFRQGVVLQFHWKHHSRFKVRWKH\KDYHQRWLPH]RQHLQIRUPDWLRQDVVRFLDWHGZLWKWKHP7LPH]RQHLQIRUPDWLRQFRXOGRIFRXUVHEHVWRUHGDVWKHYDOXHIRUDQRWKHUNH\

Arrays$UUD\V DUH YDOXHV WKDW FDQ EHLQWHUFKDQJHDEO\XVHGIRUERWK RUGHUHG RSHUDWLRQVDV

WKRXJKWKH\ZHUHOLVWVVWDFNVRUTXHXHVDQGXQRUGHUHGRSHUDWLRQVDVWKRXJKWKH\ZHUHVHWV

,QWKHIROORZLQJGRFXPHQWWKHNH\"things"KDVDQDUUD\YDOXH

{"things" : ["pie", 3.14]}

$VZHFDQVHHIURPWKHH[DPSOHDUUD\VFDQFRQWDLQGLIIHUHQWGDWDW\SHVDVYDOXHVLQWKLVFDVHDVWULQJDQGDIORDWLQJSRLQWQXPEHU,QIDFWDUUD\YDOXHVFDQEHDQ\RIWKHVXSSRUWHGYDOXHVIRUQRUPDONH\YDOXHSDLUVHYHQQHVWHGDUUD\V

2QHRIWKHJUHDWWKLQJVDERXWDUUD\VLQGRFXPHQWVLVWKDW0RQJR'%XQGHUVWDQGVWKHLUVWUXFWXUHDQGNQRZVKRZWRUHDFKLQVLGHRIDUUD\VWRSHUIRUPRSHUDWLRQVRQ

WKHLUFRQWHQWV7KLVDOORZVXVWRTXHU\RQDUUD\VDQGEXLOGLQGH[HVXVLQJWKHLUFRQWHQWV)RULQVWDQFHLQWKHSUHYLRXVH[DPSOH0RQJR'%FDQTXHU\IRUDOOGRFXPHQWVZKHUHLVDQHOHPHQWRIWKH"things"DUUD\,IWKLVLVDFRPPRQTXHU\\RXFDQHYHQFUHDWHDQLQGH[RQWKH"things"NH\WRLPSURYHWKHTXHU\VVSHHG

0RQJR'% DOVR DOORZVDWRPLF XSGDWHV WKDW PRGLI\WKH FRQWHQWV RI DUUD\V VXFK DVUHDFKLQJLQWRWKHDUUD\DQGFKDQJLQJWKHYDOXHSLHWRSL:HOOVHHPRUHH[DPSOHVRIWKHVHW\SHVRIRSHUDWLRQVWKURXJKRXWWKHWH[W

Data Types | 19
http://www.ecmascript.org/http://www.ecmascript.org/http://www.ecmascript.org/http://www.ecmascript.org/


25/48

Embedded Documents(PEHGGHGGRFXPHQWVDUHHQWLUH0RQJR'%GRFXPHQWVWKDWDUHXVHGDVWKHYDOXHIRUDNH\LQDQRWKHUGRFXPHQW7KH\FDQEHXVHGWRRUJDQL]HGDWDLQDPRUHQDWXUDOZD\WKDQMXVWDIODWVWUXFWXUH

)RUH[DPSOHLIZHKDYHDGRFXPHQWUHSUHVHQWLQJDSHUVRQDQGZDQWWRVWRUHKLVDGGUHVVZHFDQQHVWWKLVLQIRUPDWLRQLQDQHPEHGGHG"address"GRFXPHQW

{"name" : "John Doe","address" : {

"street" : "123 Park Street","city" : "Anytown","state" : "NY"

}}

7KHYDOXHIRUWKH"address"NH\LQWKHSUHYLRXVH[DPSOHLVDQRWKHUGRFXPHQWZLWKLWV

RZQYDOXHVIRU"street""city"DQG"state"$VZLWKDUUD\V0RQJR'%XQGHUVWDQGVWKHVWUXFWXUHRIHPEHGGHGGRFXPHQWVDQGLVDEOHWRUHDFKLQVLGHRIWKHPWREXLOGLQGH[HVSHUIRUPTXHULHVRUPDNHXSGDWHV

:HOOGLVFXVVVFKHPDGHVLJQLQGHSWKODWHUEXWHYHQIURPWKLVEDVLFH[DPSOHZHFDQEHJLQWRVHHKRZHPEHGGHGGRFXPHQWVFDQFKDQJHWKHZD\ZHZRUNZLWKGDWD,QDUHODWLRQDOGDWDEDVHWKHSUHYLRXVGRFXPHQWZRXOGSUREDEO\EHPRGHOHGDVWZRVHSDUDWHURZVLQWZRGLIIHUHQWWDEOHVRQHIRUSHRSOHDQGRQHIRUDGGUHVVHV:LWK0RQJR'%ZHFDQHPEHGWKHDGGUHVVGRFXPHQWGLUHFWO\ZLWKLQWKHSHUVRQGRFXPHQW:KHQXVHGSURSHUO\HPEHGGHGGRFXPHQWVFDQSURYLGHDPRUHQDWXUDODQGRIWHQPRUHHIILFLHQWUHSUHVHQWDWLRQRILQIRUPDWLRQ

7KHIOLSVLGHRIWKLVLVWKDWZHDUHEDVLFDOO\GHQRUPDOL]LQJVRWKHUHFDQEHPRUHGDWDUHSHWLWLRQZLWK0RQJR'%6XSSRVHDGGUHVVHVZHUHDVHSDUDWHWDEOHLQDUHODWLRQDOGDWDEDVHDQGZHQHHGHGWRIL[DW\SRLQDQDGGUHVV:KHQZHGLGDMRLQZLWKSHRSOHDQG DGGUHVVHV ZHG JHW WKH XSGDWHG DGGUHVV IRU HYHU\RQH ZKR VKDUHV LW :LWK0RQJR'%ZHGQHHGWRIL[WKHW\SRLQHDFKSHUVRQVGRFXPHQW

_id and ObjectIds(YHU\GRFXPHQWVWRUHGLQ0RQJR'%PXVWKDYHDQ"_id"NH\7KH"_id"NH\VYDOXHFDQEHDQ\W\SHEXWLWGHIDXOWVWRDQObjectId,QDVLQJOHFROOHFWLRQHYHU\GRFXPHQW

PXVWKDYHDXQLTXHYDOXHIRU"_id"ZKLFKHQVXUHVWKDWHYHU\GRFXPHQWLQDFROOHFWLRQFDQEHXQLTXHO\LGHQWLILHG7KDWLVLI\RXKDGWZRFROOHFWLRQVHDFKRQHFRXOGKDYHDGRFXPHQWZKHUHWKHYDOXHIRU"_id"ZDV+RZHYHUQHLWKHUFROOHFWLRQFRXOGFRQWDLQPRUHWKDQRQHGRFXPHQWZKHUH"_id"ZDV



26/48

ObjectIds

ObjectIdLVWKHGHIDXOWW\SHIRU"_id",WLVGHVLJQHGWREHOLJKWZHLJKWZKLOHVWLOOEHLQJHDV\WRJHQHUDWHLQDJOREDOO\XQLTXHZD\DFURVVGLVSDUDWHPDFKLQHV7KLVLVWKHPDLQUHDVRQZK\0RQJR'%XVHVObjectIdVDVRSSRVHGWRVRPHWKLQJPRUHWUDGLWLRQDOOLNHDQDXWRLQFUHPHQWLQJSULPDU\NH\LWLVGLIILFXOWDQGWLPHFRQVXPLQJWRV\QFKURQL]H

DXWRLQFUHPHQWLQJSULPDU\NH\VDFURVVPXOWLSOHVHUYHUV%HFDXVH0RQJR'%ZDVGHVLJQHGIURPWKHEHJLQQLQJWREHDGLVWULEXWHGGDWDEDVHGHDOLQJZLWKPDQ\QRGHVLVDQLPSRUWDQWFRQVLGHUDWLRQ7KHObjectIdW\SHDVZHOOVHHLVHDV\WRJHQHUDWHLQDVKDUGHGHQYLURQPHQW

ObjectIdVXVHE\WHVRIVWRUDJHZKLFKJLYHVWKHPDVWULQJUHSUHVHQWDWLRQWKDWLVKH[DGHFLPDOGLJLWVGLJLWVIRUHDFKE\WH7KLVFDXVHVWKHPWRDSSHDUODUJHUWKDQWKH\DUHZKLFKPDNHVVRPHSHRSOHQHUYRXV,WVLPSRUWDQW WRQRWHWKDWHYHQWKRXJKDQObjectIdLVRIWHQUHSUHVHQWHGDVDJLDQWKH[DGHFLPDOVWULQJWKHVWULQJLVDFWXDOO\WZLFHDVORQJDVWKHGDWDEHLQJVWRUHG

,I\RXFUHDWHPXOWLSOHQHZObjectIdVLQUDSLGVXFFHVVLRQ\RXFDQVHHWKDWRQO\WKHODVWIHZ GLJLWV FKDQJH HDFK WLPH ,Q DGGLWLRQ D FRXSOH RI GLJLWV LQ WKH PLGGOH RI WKHObjectIdZLOOFKDQJHLI\RXVSDFHWKHFUHDWLRQVRXWE\DFRXSOHRIVHFRQGV7KLVLVEHFDXVHRIWKHPDQQHULQZKLFKObjectIdVDUHFUHDWHG7KHE\WHVRIDQObjectIdDUHJHQHUDWHGDVIROORZV

0 1 2 3 4 5 6 7 8 9 10 11

Timestamp Machine PID Increment

7KHILUVWIRXUE\WHVRIDQObjectIdDUHDWLPHVWDPSLQVHFRQGVVLQFHWKHHSRFK7KLV

SURYLGHVDFRXSOHRIXVHIXOSURSHUWLHV 7KHWLPHVWDPSZKHQFRPELQHGZLWKWKHQH[WILYHE\WHVZKLFKZLOOEHGHVFULEHG

LQDPRPHQWSURYLGHVXQLTXHQHVVDWWKHJUDQXODULW\RIDVHFRQG

%HFDXVHWKHWLPHVWDPSFRPHVILUVW LWPHDQVWKDWObjectIdVZLOOVRUWLQURXJKO\LQVHUWLRQRUGHU7KLVLVQRWDVWURQJJXDUDQWHHEXWGRHVKDYHVRPHQLFHSURSHUWLHVVXFKDVPDNLQJObjectIdVHIILFLHQWWRLQGH[

,QWKHVHIRXUE\WHVH[LVWVDQLPSOLFLWWLPHVWDPSRIZKHQHDFKGRFXPHQWZDVFUHDWHG 0RVW GULYHUV H[SRVH D PHWKRG IRU H[WUDFWLQJ WKLV LQIRUPDWLRQ IURP DQObjectId

%HFDXVHWKHFXUUHQWWLPHLVXVHGLQObjectIdVVRPHXVHUVZRUU\WKDWWKHLUVHUYHUVZLOOQHHGWRKDYHV\QFKURQL]HGFORFNV7KLVLVQRWQHFHVVDU\EHFDXVHWKHDFWXDOYDOXHRIWKHWLPHVWDPSGRHVQWPDWWHURQO\WKDWLWLVRIWHQQHZRQFHSHUVHFRQGDQGLQFUHDVLQJ

7KHQH[WWKUHHE\WHVRIDQObjectIdDUHDXQLTXHLGHQWLILHURIWKHPDFKLQHRQZKLFKLWZDVJHQHUDWHG7KLVLVXVXDOO\DKDVKRIWKHPDFKLQHVKRVWQDPH%\LQFOXGLQJWKHVHE\WHVZHJXDUDQWHHWKDWGLIIHUHQWPDFKLQHVZLOOQRWJHQHUDWHFROOLGLQJObjectIdV

Data Types | 21


27/48

7RSURYLGHXQLTXHQHVVDPRQJGLIIHUHQWSURFHVVHVJHQHUDWLQJObjectIdVFRQFXUUHQWO\RQDVLQJOHPDFKLQHWKHQH[WWZRE\WHVDUHWDNHQIURPWKHSURFHVVLGHQWLILHU3,'RIWKHObjectIdJHQHUDWLQJSURFHVV

7KHVHILUVWQLQHE\WHVRIDQObjectIdJXDUDQWHHLWVXQLTXHQHVVDFURVVPDFKLQHVDQGSURFHVVHVIRUDVLQJOHVHFRQG7KHODVWWKUHHE\WHVDUHVLPSO\DQLQFUHPHQWLQJFRXQWHU

WKDWLVUHVSRQVLEOHIRUXQLTXHQHVVZLWKLQDVHFRQGLQDVLQJOHSURFHVV7KLVDOORZVIRUXSWRXQLTXHObjectIdVWREHJHQHUDWHGSHUSURFHVVLQDVLQJOHVHFRQG

Autogeneration of _id

$VVWDWHGSUHYLRXVO\LIWKHUHLVQR"_id"NH\SUHVHQWZKHQDGRFXPHQWLVLQVHUWHGRQHZLOOEHDXWRPDWLFDOO\DGGHGWRWKHLQVHUWHGGRFXPHQW7KLVFDQEHKDQGOHGE\WKH0RQJR'%VHUYHUEXWZLOOJHQHUDOO\EHGRQHE\WKHGULYHURQWKHFOLHQWVLGH7KHUHDUHDFRXSOHRIUHDVRQVIRUWKDW

$OWKRXJKObjectIdVDUHGHVLJQHGWREHOLJKWZHLJKWDQGHDV\WRJHQHUDWHWKHUHLV

VWLOOVRPHRYHUKHDGLQYROYHGLQWKHLUJHQHUDWLRQ7KHGHFLVLRQWRJHQHUDWHWKHPRQWKHFOLHQWVLGHUHIOHFWVDQRYHUDOOSKLORVRSK\RI0RQJR'%ZRUNVKRXOGEHSXVKHGRXWRIWKHVHUYHUDQGWRWKHGULYHUVZKHQHYHUSRVVLEOH7KLVSKLORVRSK\UHIOHFWVWKHIDFWWKDWHYHQZLWKVFDODEOHGDWDEDVHVOLNH0RQJR'%LWLVHDVLHUWRVFDOHRXWDWWKHDSSOLFDWLRQOD\HUWKDQDWWKHGDWDEDVHOD\HU0RYLQJZRUNWRWKHFOLHQWVLGHUHGXFHVWKHEXUGHQUHTXLULQJWKHGDWDEDVHWRVFDOH

%\JHQHUDWLQJObjectIdVRQWKHFOLHQWVLGHGULYHUVDUHFDSDEOHRISURYLGLQJULFKHU$3,V WKDQ ZRXOG EH RWKHUZLVH SRVVLEOH )RU H[DPSOH D GULYHU PLJKW KDYH LWVinsertPHWKRGHLWKHUUHWXUQWKHJHQHUDWHG ObjectIdRULQMHFWLWGLUHFWO\LQWRWKHGRFXPHQW WKDW ZDV LQVHUWHG ,I WKH GULYHU DOORZHG WKH VHUYHU WR JHQHUDWH

ObjectIdVWKHQ D VHSDUDWH TXHU\ ZRXOG EHUHTXLUHGWR GHWHUPLQHWKH YDOXH RI"_id"IRUDQLQVHUWHGGRFXPHQW



28/48

CHAPTER 4

Querying

7KLVFKDSWHUORRNVDWTXHU\LQJLQGHWDLO7KHPDLQDUHDVFRYHUHGDUHDVIROORZV


29/48

HDV\DVVSHFLI\LQJWKHYDOXHWKDW\RXDUHORRNLQJIRU)RUH[DPSOHWRILQGDOOGRFXPHQWVZKHUHWKHYDOXHIRU"age"LVZHFDQDGGWKDWNH\YDOXHSDLUWRWKHTXHU\GRFXPHQW

> db.users.find({"age" : 27})

,IZHKDYHDVWULQJZHZDQWWRPDWFKVXFKDVD"username"NH\ZLWKWKHYDOXH"joe"ZHXVHWKDWNH\YDOXHSDLULQVWHDG

> db.users.find({"username" : "joe"})

0XOWLSOHFRQGLWLRQVFDQEHVWUXQJWRJHWKHUE\DGGLQJPRUHNH\YDOXHSDLUVWRWKHTXHU\GRFXPHQW ZKLFK JHWV LQWHUSUHWHG DV FRQGLWLRQ $1' FRQGLWLRQ $1' $1'FRQGLWLRQ1)RULQVWDQFHWRJHWDOOXVHUVZKRDUH\HDUROGVZLWKWKHXVHUQDPHMRHZHFDQTXHU\IRUWKHIROORZLQJ

> db.users.find({"username" : "joe", "age" : 27})

Specifying Which Keys to Return

6RPHWLPHV\RXGRQRWQHHGDOORIWKHNH\YDOXHSDLUVLQDGRFXPHQWUHWXUQHG,IWKLVLVWKHFDVH\RXFDQSDVVDVHFRQGDUJXPHQWWRfindRUfindOneVSHFLI\LQJWKHNH\V\RXZDQW7KLVUHGXFHVERWKWKHDPRXQWRIGDWDVHQWRYHUWKHZLUHDQGWKHWLPHDQGPHPRU\XVHGWRGHFRGHGRFXPHQWVRQWKHFOLHQWVLGH

)RUH[DPSOHLI\RXKDYHDXVHUFROOHFWLRQDQG\RXDUHLQWHUHVWHGRQO\LQWKH"username"DQG"email"NH\V\RXFRXOGUHWXUQMXVWWKRVHNH\VZLWKWKHIROORZLQJTXHU\

> db.users.find({}, {"username" : 1, "email" : 1}){

"_id" : ObjectId("4ba0f0dfd22aa494fd523620"),"username" : "joe","email" : "[email protected]"

}

$V\RXFDQVHHIURPWKHSUHYLRXVRXWSXWWKH"_id"NH\LVDOZD\VUHWXUQHGHYHQLILWLVQWVSHFLILFDOO\OLVWHG

db.users.find({}, {"fatal_weakness" : 0})

7KLVFDQHYHQSUHYHQW"_id"IURPEHLQJUHWXUQHG

> db.users.find({}, {"username" : 1, "_id" : 0}){"username" : "joe",

}

46 | Chapter 4:Querying


30/48

Limitations7KHUHDUHVRPHUHVWULFWLRQVRQTXHULHV7KHYDOXHRIDTXHU\GRFXPHQWPXVWEHDFRQVWDQWDVIDUDVWKHGDWDEDVHLVFRQFHUQHG,WFDQEHDQRUPDOYDULDEOHLQ\RXURZQFRGH7KDWLVLWFDQQRWUHIHUWRWKHYDOXHRIDQRWKHUNH\LQWKHGRFXPHQW)RUH[DPSOHLIZHZHUHNHHSLQJLQYHQWRU\DQGZHKDGERWK"in_stock"DQG"num_sold"NH\VZHFRXOGFRPSDUHWKHLUYDOXHVE\TXHU\LQJWKHIROORZLQJ

> db.stock.find({"in_stock" : "this.num_sold"}) // doesn't work

7KHUHDUHZD\VWRGRWKLVVHHZKHUH4XHULHVRQSDJHEXW\RXZLOOXVXDOO\JHWEHWWHUSHUIRUPDQFHE\UHVWUXFWXULQJ\RXUGRFXPHQWVOLJKWO\VXFKWKDWDQRUPDOTXHU\ZLOO VXIILFH ,Q WKLV H[DPSOH ZH FRXOG LQVWHDG XVH WKH NH\V "initial_stock" DQG"in_stock"7KHQHYHU\WLPHVRPHRQHEX\VDQLWHPZHGHFUHPHQWWKHYDOXHRIWKH"in_stock"NH\E\RQH)LQDOO\ZHFDQGRDVLPSOHTXHU\WRFKHFNZKLFKLWHPVDUHRXWRIVWRFN

> db.stock.find({"in_stock" : 0})

Query Criteria4XHULHVFDQJREH\RQGWKHH[DFWPDWFKLQJGHVFULEHGLQWKHSUHYLRXVVHFWLRQWKH\FDQPDWFKPRUHFRPSOH[FULWHULDVXFKDVUDQJHV25FODXVHVDQGQHJDWLRQ

Query Conditionals"$lt""$lte""$gt"DQG"$gte"DUHDOOFRPSDULVRQRSHUDWRUVFRUUHVSRQGLQJWR!DQG!UHVSHFWLYHO\7KH\FDQEHFRPELQHGWRORRNIRUDUDQJHRIYDOXHV)RUH[

DPSOHWRORRNIRUXVHUVZKRDUHEHWZHHQWKHDJHVRIDQGLQFOXVLYHZHFDQGRWKLV> db.users.find({"age" : {"$gte" : 18, "$lte" : 30}})

7KHVHW\SHVRIUDQJHTXHULHVDUHRIWHQXVHIXOIRUGDWHV)RUH[DPSOHWRILQGSHRSOHZKRUHJLVWHUHGEHIRUH-DQXDU\ZHFDQGRWKLV

> start = new Date("01/01/2007")> db.users.find({"registered" : {"$lt" : start}})

$QH[DFWPDWFKRQDGDWHLVOHVVXVHIXOEHFDXVHGDWHVDUHRQO\VWRUHGZLWKPLOOLVHFRQGSUHFLVLRQ 2IWHQ \RX ZDQW D ZKROH GD\ ZHHN RU PRQWK PDNLQJ D UDQJH TXHU\QHFHVVDU\

7RTXHU\IRUGRFXPHQWVZKHUHDNH\VYDOXHLVQRWHTXDOWRDFHUWDLQYDOXH\RXPXVWXVHDQRWKHUFRQGLWLRQDORSHUDWRU"$ne"ZKLFKVWDQGVIRUQRWHTXDO,I\RXZDQWWRILQGDOOXVHUVZKRGRQRWKDYHWKHXVHUQDPHMRH\RXFDQTXHU\IRUWKHPXVLQJWKLV

> db.users.find({"username" : {"$ne" : "joe"}})

"$ne"FDQEHXVHGZLWKDQ\W\SH

Query Criteria | 47


31/48

OR Queries7KHUHDUHWZRZD\VWRGRDQ25TXHU\LQ0RQJR'%"$in"FDQEHXVHGWRTXHU\IRUDYDULHW\RIYDOXHVIRUDVLQJOHNH\"$or"LVPRUHJHQHUDOLWFDQEHXVHGWRTXHU\IRUDQ\RIWKHJLYHQYDOXHVDFURVVPXOWLSOHNH\V

,I\RXKDYHPRUHWKDQRQHSRVVLEOHYDOXHWRPDWFKIRUDVLQJOHNH\XVHDQDUUD\RIFULWHULDZLWK"$in")RULQVWDQFHVXSSRVHZHZHUHUXQQLQJDUDIIOHDQGWKHZLQQLQJWLFNHWQXPEHUVZHUHDQG7RILQGDOOWKUHHRIWKHVHGRFXPHQWVZHFDQFRQVWUXFWWKHIROORZLQJTXHU\

> db.raffle.find({"ticket_no" : {"$in" : [725, 542, 390]}})

"$in"LVYHU\IOH[LEOHDQGDOORZV\RXWRVSHFLI\FULWHULDRIGLIIHUHQWW\SHVDVZHOODVYDOXHV)RUH[DPSOHLIZHDUHJUDGXDOO\PLJUDWLQJRXUVFKHPDWRXVHXVHUQDPHVLQVWHDGRIXVHU,'QXPEHUVZHFDQTXHU\IRUHLWKHUE\XVLQJWKLV

> db.users.find({"user_id" : {"$in" : [12345, "joe"]})

7KLVPDWFKHVGRFXPHQWVZLWKD"user_id"HTXDOWRDQGGRFXPHQWVZLWKD"user_id"HTXDOWR"joe"

,I"$in"LVJLYHQDQDUUD\ZLWKDVLQJOHYDOXHLWEHKDYHVWKHVDPHDVGLUHFWO\PDWFKLQJWKHYDOXH)RULQVWDQFH{ticket_no : {$in : [725]}}PDWFKHVWKHVDPHGRFXPHQWVDV{ticket_no : 725}

7KHRSSRVLWHRI"$in"LV"$nin"ZKLFKUHWXUQVGRFXPHQWVWKDWGRQWPDWFKDQ\RIWKHFULWHULDLQWKHDUUD\,IZHZDQWWRUHWXUQDOORIWKHSHRSOHZKRGLGQWZLQDQ\WKLQJLQWKHUDIIOHZHFDQTXHU\IRUWKHPZLWKWKLV

> db.raffle.find({"ticket_no" : {"$nin" : [725, 542, 390]}})

7KLVTXHU\UHWXUQVHYHU\RQHZKRGLGQRWKDYHWLFNHWVZLWKWKRVHQXPEHUV

"$in"JLYHV\RXDQ25TXHU\IRUDVLQJOHNH\EXWZKDWLIZHQHHGWRILQGGRFXPHQWVZKHUH"ticket_no"LVRU"winner"LVtrue")RUWKLVW\SHRITXHU\ZHOOQHHGWRXVHWKH"$or"FRQGLWLRQDO"$or"WDNHVDQDUUD\RISRVVLEOHFULWHULD,QWKHUDIIOHFDVHXVLQJ"$or"ZRXOGORRNOLNHWKLV

> db.raffle.find({"$or" : [{"ticket_no" : 725}, {"winner" : true}]})

"$or"FDQFRQWDLQRWKHUFRQGLWLRQDOV,IIRUH[DPSOHZHZDQWWRPDWFKDQ\RIWKHWKUHH"ticket_no"YDOXHVRUWKH"winner"NH\ZHFDQXVHWKLV

> db.raffle.find({"$or" : [{"ticket_no" : {"$in" : [725, 542, 390]}},

{"winner" : true}]})

:LWKDQRUPDO$1'W\SHTXHU\\RXZDQWWRQDUURZ\RXUUHVXOWVGRZQDVIDUDVSRVVLEOHLQDVIHZDUJXPHQWVDVSRVVLEOH25W\SHTXHULHVDUHWKHRSSRVLWHWKH\DUHPRVWHIILFLHQWLIWKHILUVWDUJXPHQWVPDWFKDVPDQ\GRFXPHQWVDVSRVVLEOH



32/48

$not"$not"LVDPHWDFRQGLWLRQDOLWFDQEHDSSOLHGRQWRSRIDQ\RWKHUFULWHULD$VDQH[DPSOHOHWVFRQVLGHUWKHPRGXOXVRSHUDWRU"$mod""$mod"TXHULHVIRUNH\VZKRVHYDOXHVZKHQGLYLGHGE\WKHILUVWYDOXHJLYHQKDYHDUHPDLQGHURIWKHVHFRQGYDOXH

> db.users.find({"id_num" : {"$mod" : [5, 1]}})7KHSUHYLRXVTXHU\UHWXUQVXVHUVZLWK"id_num"VRIDQGVRRQ,IZHZDQWLQVWHDGWRUHWXUQXVHUVZLWK"id_num"VRIDQGVRRQZHFDQXVH"$not"

> db.users.find({"id_num" : {"$not" : {"$mod" : [5, 1]}}})

"$not"FDQEHSDUWLFXODUO\XVHIXOLQFRQMXQFWLRQZLWKUHJXODUH[SUHVVLRQVWRILQGDOOGRFXPHQWVWKDWGRQWPDWFKDJLYHQSDWWHUQUHJXODUH[SUHVVLRQXVDJHLVGHVFULEHGLQWKHVHFWLRQ5HJXODU([SUHVVLRQVRQSDJH

Rules for Conditionals,I\RXORRNDWWKHXSGDWHPRGLILHUVLQWKHSUHYLRXVFKDSWHUDQGSUHYLRXVTXHU\GRFXPHQWV\RXOOQRWLFHWKDWWKHSUHIL[HGNH\VDUHLQGLIIHUHQWSRVLWLRQV,QWKHTXHU\"$lt"LVLQWKHLQQHUGRFXPHQWLQWKHXSGDWH"$inc"LVWKHNH\IRUWKHRXWHUGRFXPHQW7KLVJHQHUDOO\KROGVWUXHFRQGLWLRQDOVDUHDQLQQHUGRFXPHQWNH\DQGPRGLILHUVDUHDOZD\VDNH\LQWKHRXWHUGRFXPHQW

0XOWLSOHFRQGLWLRQVFDQEHSXWRQDVLQJOHNH\)RUH[DPSOHWRILQGDOOXVHUVEHWZHHQWKHDJHVRIDQGZHFDQTXHU\IRUERWK"$gt"DQG"$lt"RQWKH"age"NH\

> db.users.find({"age" : {"$lt" : 30, "$gt" : 20}})

$Q\QXPEHURIFRQGLWLRQDOVFDQEHXVHGZLWKDVLQJOHNH\0XOWLSOHXSGDWHPRGLILHUVFDQQRWEHXVHGRQD VLQJOHNH\KRZHYHU)RUH[DPSOH\RXFDQQRWKDYHDPRGLILHUGRFXPHQW VXFK DV {"$inc" : {"age" : 1}, "$set" : {age : 40}} EHFDXVH LWPRGLILHV"age"WZLFH:LWKTXHU\FRQGLWLRQDOVQRVXFKUXOHDSSOLHV

Type-Specific Queries$VFRYHUHGLQ&KDSWHU0RQJR'%KDVDZLGHYDULHW\RIW\SHVWKDWFDQEHXVHGLQDGRFXPHQW6RPHRIWKHVHEHKDYHVSHFLDOO\LQTXHULHV

nullnullEHKDYHVDELWVWUDQJHO\,WGRHVPDWFKLWVHOIVRLIZHKDYHDFROOHFWLRQZLWKWKHIROORZLQJGRFXPHQWV

> db.c.find(){ "_id" : ObjectId("4ba0f0dfd22aa494fd523621"), "y" : null }

Type-Specific Queries | 49


33/48

{ "_id" : ObjectId("4ba0f0dfd22aa494fd523622"), "y" : 1 }{ "_id" : ObjectId("4ba0f148d22aa494fd523623"), "y" : 2 }

ZHFDQTXHU\IRUGRFXPHQWVZKRVH"y"NH\LVnullLQWKHH[SHFWHGZD\

> db.c.find({"y" : null}){ "_id" : ObjectId("4ba0f0dfd22aa494fd523621"), "y" : null }

+RZHYHUnullQRWRQO\PDWFKHVLWVHOIEXWDOVRPDWFKHVGRHVQRWH[LVW7KXVTXHU\LQJIRUDNH\ZLWKWKHYDOXHnullZLOOUHWXUQDOOGRFXPHQWVODFNLQJWKDWNH\

> db.c.find({"z" : null}){ "_id" : ObjectId("4ba0f0dfd22aa494fd523621"), "y" : null }{ "_id" : ObjectId("4ba0f0dfd22aa494fd523622"), "y" : 1 }{ "_id" : ObjectId("4ba0f148d22aa494fd523623"), "y" : 2 }

,IZHRQO\ZDQWWRILQGNH\VZKRVHYDOXHLVnullZHFDQFKHFNWKDWWKHNH\LVnullDQGH[LVWVXVLQJWKH"$exists"FRQGLWLRQDO

> db.c.find({"z" : {"$in" : [null], "$exists" : true}})

8QIRUWXQDWHO\ WKHUH LV QR"$eq" RSHUDWRUZKLFK PDNHV WKLV D OLWWOH DZNZDUG EXW"$in"ZLWKRQHHOHPHQWLVHTXLYDOHQW

Regular Expressions5HJXODUH[SUHVVLRQVDUHXVHIXOIRUIOH[LEOHVWULQJPDWFKLQJ)RUH[DPSOHLIZHZDQWWRILQGDOOXVHUVZLWKWKHQDPH-RHRU MRHZHFDQXVHDUHJXODUH[SUHVVLRQWRGRFDVHLQVHQVLWLYHPDWFKLQJ

> db.users.find({"name" : /joe/i})

5HJXODUH[SUHVVLRQIODJViDUHDOORZHGEXWQRWUHTXLUHG,IZHZDQWWRPDWFKQRWRQO\

YDULRXVFDSLWDOL]DWLRQVRIMRHEXWDOVRMRH\ZHFDQFRQWLQXHWRLPSURYHRXUUHJXODUH[SUHVVLRQ

> db.users.find({"name" : /joey?/i})

0RQJR'%XVHVWKH3HUO&RPSDWLEOH5HJXODU([SUHVVLRQ3&5(OLEUDU\WRPDWFKUHJXODU H[SUHVVLRQV DQ\ UHJXODU H[SUHVVLRQ V\QWD[ DOORZHG E\ 3&5( LV DOORZHG LQ0RQJR'%,WLVDJRRGLGHDWRFKHFN\RXUV\QWD[ZLWKWKH-DYD6FULSWVKHOOEHIRUHXVLQJLWLQDTXHU\WRPDNHVXUHLWPDWFKHVZKDW\RXWKLQNLWPDWFKHV

0RQJR'%FDQOHYHUDJHDQLQGH[IRUTXHULHVRQSUHIL[UHJXODUH[SUHV

VLRQVHJ/^joey/VRTXHULHVRIWKDWNLQGFDQEHIDVW

5HJXODUH[SUHVVLRQVFDQDOVRPDWFKWKHPVHOYHV9HU\IHZSHRSOHLQVHUWUHJXODUH[SUHVVLRQVLQWRWKHGDWDEDVHEXWLI\RXLQVHUWRQH\RXFDQPDWFKLWZLWKLWVHOI

> db.foo.insert({"bar" : /baz/})> db.foo.find({"bar" : /baz/})



34/48

{"_id" : ObjectId("4b23c3ca7525f35f94b60a2d"),"bar" : /baz/

}

Querying Arrays4XHU\LQJIRUHOHPHQWVRIDQDUUD\LVVLPSOH$QDUUD\FDQPRVWO\EHWUHDWHGDVWKRXJKHDFKHOHPHQWLVWKHYDOXHRIWKHRYHUDOONH\)RUH[DPSOHLIWKHDUUD\LVDOLVWRIIUXLWVOLNHWKLV

> db.food.insert({"fruit" : ["apple", "banana", "peach"]})

WKHIROORZLQJTXHU\

> db.food.find({"fruit" : "banana"})

ZLOOVXFFHVVIXOO\PDWFKWKHGRFXPHQW:HFDQTXHU\IRULWLQPXFKWKHVDPHZD\DVWKRXJKZHKDGDGRFXPHQWWKDWORRNHGOLNHWKHLOOHJDOGRFXPHQW{"fruit" : "apple",

"fruit" : "banana", "fruit" : "peach"}

$all

,I\RXQHHGWRPDWFKDUUD\VE\PRUHWKDQRQHHOHPHQW\RXFDQXVH "$all"7KLVDOORZV\RXWRPDWFKDOLVWRIHOHPHQWV)RUH[DPSOHVXSSRVHZHFUHDWHGDFROOHFWLRQZLWKWKUHHHOHPHQWV

> db.food.insert({"_id" : 1, "fruit" : ["apple", "banana", "peach"]})> db.food.insert({"_id" : 2, "fruit" : ["apple", "kumquat", "orange"]})> db.food.insert({"_id" : 3, "fruit" : ["cherry", "banana", "apple"]})

7KHQZHFDQILQGDOOGRFXPHQWVZLWKERWK"apple"DQG"banana"HOHPHQWVE\TXHU\LQJ

ZLWK"$all"

> db.food.find({fruit : {$all : ["apple", "banana"]}}){"_id" : 1, "fruit" : ["apple", "banana", "peach"]}{"_id" : 3, "fruit" : ["cherry", "banana", "apple"]}

2UGHUGRHVQRWPDWWHU1RWLFH "banana"FRPHVEHIRUH"apple"LQWKHVHFRQGUHVXOW8VLQJDRQHHOHPHQWDUUD\ZLWK"$all"LVHTXLYDOHQWWRQRWXVLQJ"$all")RULQVWDQFH{fruit : {$all : ['apple']}ZLOOPDWFKWKHVDPHGRFXPHQWVDV{fruit : 'apple'}

db.food.find({"fruit" : ["apple", "banana", "peach"]})

%XWWKLVZLOOQRW

> db.food.find({"fruit" : ["apple", "banana"]})

DQGQHLWKHUZLOOWKLV

> db.food.find({"fruit" : ["banana", "apple", "peach"]})



35/48

,I\RXZDQWWRTXHU\IRUDVSHFLILFHOHPHQWRIDQDUUD\\RXFDQVSHFLI\DQLQGH[XVLQJWKHV\QWD[keyindex

> db.food.find({"fruit.2" : "peach"})

$UUD\VDUHDOZD\VLQGH[HGVRWKLVZRXOGPDWFKWKHWKLUGDUUD\HOHPHQWDJDLQVWWKHVWULQJ"peach"

$size

$XVHIXOFRQGLWLRQDOIRUTXHU\LQJDUUD\VLV"$size"ZKLFKDOORZV\RXWRTXHU\IRUDUUD\VRIDJLYHQVL]H+HUHVDQH[DPSOH

> db.food.find({"fruit" : {"$size" : 3}})

2QHFRPPRQTXHU\LVWRJHWDUDQJHRIVL]HV"$size"FDQQRWEHFRPELQHGZLWKDQRWKHUFRQGLWLRQDOLQWKLVH[DPSOH "$gt"EXWWKLVTXHU\FDQEHDFFRPSOLVKHGE\DGGLQJD"size"NH\WRWKHGRFXPHQW7KHQHYHU\WLPH\RXDGGDQHOHPHQWWRWKHDUUD\LQFUHPHQWWKHYDOXHRI"size",IWKHRULJLQDOXSGDWHORRNHGOLNHWKLV

> db.food.update({"$push" : {"fruit" : "strawberry"}})

LWFDQVLPSO\EHFKDQJHGWRWKLV

> db.food.update({"$push" : {"fruit" : "strawberry"}, "$inc" : {"size" : 1}})

,QFUHPHQWLQJLVH[WUHPHO\IDVWVRDQ\SHUIRUPDQFHSHQDOW\LVQHJOLJLEOH6WRULQJGRFXPHQWVOLNHWKLVDOORZV\RXWRGRTXHULHVVXFKDVWKLV

> db.food.find({"size" : {"$gt" : 3}})

8QIRUWXQDWHO\WKLVWHFKQLTXHGRHVQWZRUNDVZHOOZLWKWKH"$addToSet"RSHUDWRU

The $slice operator$VPHQWLRQHGHDUOLHULQWKLVFKDSWHUWKHRSWLRQDOVHFRQGDUJXPHQWWRfindVSHFLILHVWKHNH\VWREHUHWXUQHG7KHVSHFLDO"$slice"RSHUDWRUFDQEHXVHGWRUHWXUQDVXEVHWRIHOHPHQWVIRUDQDUUD\NH\

)RUH[DPSOHVXSSRVHZHKDGDEORJSRVWGRFXPHQWDQGZHZDQWHGWRUHWXUQWKHILUVWFRPPHQWV

> db.blog.posts.findOne(criteria, {"comments" : {"$slice" : 10}})

$OWHUQDWLYHO\LIZHZDQWHGWKHODVWFRPPHQWVZHFRXOGXVH

> db.blog.posts.findOne(criteria, {"comments" : {"$slice" : -10}})

"$slice"FDQDOVRUHWXUQSDJHVLQWKHPLGGOHRIWKHUHVXOWVE\WDNLQJDQRIIVHWDQGWKHQXPEHURIHOHPHQWVWRUHWXUQ

> db.blog.posts.findOne(criteria, {"comments" : {"$slice" : [23, 10]}})

7KLVZRXOGVNLSWKHILUVWHOHPHQWVDQGUHWXUQWKHWKWKURXJKWK,IWKHUHDUHIHZHUWKDQHOHPHQWVLQWKHDUUD\LWZLOOUHWXUQDVPDQ\DVSRVVLEOH



36/48

8QOHVVRWKHUZLVHVSHFLILHGDOONH\VLQDGRFXPHQWDUHUHWXUQHGZKHQ"$slice"LVXVHG7KLVLVXQOLNHWKHRWKHUNH\VSHFLILHUVZKLFKVXSSUHVVXQPHQWLRQHGNH\VIURPEHLQJUHWXUQHG)RULQVWDQFHLIZHKDGDEORJSRVWGRFXPHQWWKDWORRNHGOLNHWKLV

{"_id" : ObjectId("4b2d75476cc613d5ee930164"),"title" : "A blog post","content" : "...","comments" : [

{"name" : "joe","email" : "[email protected]","content" : "nice post."

},{

"name" : "bob","email" : "[email protected]","content" : "good post."

}]

}

DQGZHGLGD"$slice"WRJHWWKHODVWFRPPHQWZHGJHWWKLV

> db.blog.posts.findOne(criteria, {"comments" : {"$slice" : -1}}){

"_id" : ObjectId("4b2d75476cc613d5ee930164"),"title" : "A blog post","content" : "...","comments" : [

{"name" : "bob","email" : "[email protected]",

"content" : "good post."}]

}

%RWK"title"DQG"content"DUHVWLOOUHWXUQHGHYHQWKRXJKWKH\ZHUHQWH[SOLFLWO\LQFOXGHGLQWKHNH\VSHFLILHU

Querying on Embedded Documents7KHUHDUHWZRZD\VRITXHU\LQJIRUDQHPEHGGHGGRFXPHQWTXHU\LQJIRUWKHZKROHGRFXPHQWRUTXHU\LQJIRULWVLQGLYLGXDONH\YDOXHSDLUV

4XHU\LQJIRUDQHQWLUHHPEHGGHGGRFXPHQWZRUNVLGHQWLFDOO\WRDQRUPDOTXHU\)RUH[DPSOHLIZHKDYHDGRFXPHQWWKDWORRNVOLNHWKLV

{"name" : {

"first" : "Joe","last" : "Schmoe"

},



37/48

"age" : 45}

ZHFDQTXHU\IRUVRPHRQHQDPHG-RH6FKPRHZLWKWKHIROORZLQJ

> db.people.find({"name" : {"first" : "Joe", "last" : "Schmoe"}})

+RZHYHULI-RHGHFLGHVWRDGGDPLGGOHQDPHNH\VXGGHQO\WKLVTXHU\ZRQWZRUNDQ\PRUHLWGRHVQWPDWFKWKHHQWLUHHPEHGGHGGRFXPHQW7KLVW\SHRITXHU\LVDOVRRUGHUVHQVLWLYH{"last" : "Schmoe", "first" : "Joe"}ZRXOGQRWEHDPDWFK

,ISRVVLEOHLWVXVXDOO\DJRRGLGHDWRTXHU\IRUMXVWDVSHFLILFNH\RUNH\VRIDQHPEHGGHGGRFXPHQW7KHQLI\RXUVFKHPDFKDQJHVDOORI\RXUTXHULHVZRQWVXGGHQO\EUHDNEHFDXVHWKH\UHQRORQJHUH[DFWPDWFKHV db.people.find({"name.first" : "Joe", "name.last" : "Schmoe"})

1RZLI-RHDGGVPRUHNH\VWKLVTXHU\ZLOOVWLOOPDWFKKLVILUVWDQGODVWQDPHV

7KLVGRWQRWDWLRQLVWKHPDLQGLIIHUHQFHEHWZHHQTXHU\GRFXPHQWVDQGRWKHUGRFXPHQWW\SHV 4XHU\ GRFXPHQWV FDQ FRQWDLQ GRWV ZKLFK PHDQ UHDFK LQWR DQ HPEHGGHGGRFXPHQW'RWQRWDWLRQLVDOVRWKHUHDVRQWKDWGRFXPHQWVWREHLQVHUWHGFDQQRWFRQWDLQWKHFKDUDFWHU2IWHQWLPHVSHRSOHUXQLQWRWKLVOLPLWDWLRQZKHQWU\LQJWRVDYH85/VDVNH\V2QHZD\WRJHWDURXQGLWLVWRDOZD\VSHUIRUPDJOREDOUHSODFHEHIRUHLQVHUWLQJRU DIWHU UHWULHYLQJ VXEVWLWXWLQJ D FKDUDFWHU WKDW LVQW OHJDO LQ 85/V IRU WKH GRW FKDUDFWHU

(PEHGGHGGRFXPHQWPDWFKHVFDQJHWDOLWWOHWULFN\DVWKHGRFXPHQWVWUXFWXUHJHWVPRUHFRPSOLFDWHG)RUH[DPSOHVXSSRVHZHDUHVWRULQJEORJSRVWVDQGZHZDQWWRILQGFRPPHQWVE\-RHWKDWZHUHVFRUHGDWOHDVWDILYH:HFRXOGPRGHOWKHSRVWDVIROORZV

> db.blog.find(){

"content" : "...","comments" : [

{"author" : "joe","score" : 3,"comment" : "nice post"

},{

"author" : "mary","score" : 6,"comment" : "terrible post"

}]

}

1RZZHFDQWTXHU\XVLQJdb.blog.find({"comments" : {"author" : "joe", "score" :{"$gte" : 5}}})(PEHGGHGGRFXPHQWPDWFKHVKDYHWRPDWFKWKHZKROHGRFXPHQWDQG WKLV GRHVQW PDWFK WKH "comment" NH\ ,W DOVR ZRXOGQW ZRUN WR GRdb.blog.find({"comments.author" : "joe", "comments.score" : {"$gte" : 5}})



38/48

EHFDXVHWKHDXWKRUFULWHULDFRXOGPDWFKDGLIIHUHQWFRPPHQWWKDQWKHVFRUHFULWHULD7KDW LV LW ZRXOG UHWXUQ WKH GRFXPHQW VKRZQ HDUOLHU LW ZRXOG PDWFK "author" :"joe"LQWKHILUVWFRPPHQWDQG"score" : 6LQWKHVHFRQGFRPPHQW

7RFRUUHFWO\JURXSFULWHULDZLWKRXWQHHGLQJWRVSHFLI\HYHU\NH\XVH"$elemMatch"7KLVYDJXHO\QDPHGFRQGLWLRQDODOORZV\RXWRSDUWLDOO\VSHFLI\FULWHULDWRPDWFKDVLQJOH

HPEHGGHGGRFXPHQWLQDQDUUD\7KHFRUUHFWTXHU\ORRNVOLNHWKLV> db.blog.find({"comments" : {"$elemMatch" : {"author" : "joe",

"score" : {"$gte" : 5}}}})

"$elemMatch"DOORZVXVWRJURXSRXUFULWHULD$VVXFKLWVRQO\QHHGHGZKHQ\RXKDYHPRUHWKDQRQHNH\\RXZDQWWRPDWFKRQLQDQHPEHGGHGGRFXPHQW

$where Queries.H\YDOXHSDLUVDUHDIDLUO\H[SUHVVLYHZD\WRTXHU\EXWWKHUHDUHVRPHTXHULHVWKDW

WKH\ FDQQRW UHSUHVHQW )RU TXHULHV WKDW FDQQRW EH GRQH DQ\ RWKHU ZD\ WKHUH DUH"$where"FODXVHVZKLFKDOORZ\RXWRH[HFXWHDUELWUDU\-DYD6FULSWDVSDUWRI\RXUTXHU\7KLVDOORZV\RXWRGRDOPRVWDQ\WKLQJZLWKLQDTXHU\

7KHPRVWFRPPRQFDVHIRUWKLVLVZDQWLQJWRFRPSDUHWKHYDOXHVIRUWZRNH\VLQDGRFXPHQWIRULQVWDQFHLIZHKDGDOLVWRILWHPVDQGZDQWHGWRUHWXUQGRFXPHQWVZKHUHDQ\WZRRIWKHYDOXHVDUHHTXDO+HUHVDQH[DPSOH

> db.foo.insert({"apple" : 1, "banana" : 6, "peach" : 3})> db.foo.insert({"apple" : 8, "spinach" : 4, "watermelon" : 4})

,QWKHVHFRQGGRFXPHQW"spinach"DQG"watermelon"KDYHWKHVDPHYDOXHVRZHGOLNHWKDWGRFXPHQWUHWXUQHG,WVXQOLNHO\0RQJR'%ZLOOHYHUKDYHDFRQGLWLRQDOIRUWKLV

VRZHFDQXVHD"$where"FODXVHWRGRLWZLWK-DYD6FULSW

> db.foo.find({"$where" : function () {... for (var current in this) {... for (var other in this) {... if (current != other && this[current] == this[other]) {... return true;... }... }... }... return false;... }});

,IWKHIXQFWLRQUHWXUQVtrueWKHGRFXPHQWZLOOEHSDUWRIWKHUHVXOWVHWLILWUHWXUQVfalseLWZRQWEH

:HXVHGDIXQFWLRQHDUOLHUEXW\RXFDQDOVRXVHVWULQJVWRVSHFLI\D "$where"TXHU\WKHIROORZLQJWZR"$where"TXHULHVDUHHTXLYDOHQW

> db.foo.find({"$where" : "this.x + this.y == 10"})> db.foo.find({"$where" : "function() { return this.x + this.y == 10; }"})

$where Queries | 55


39/48

"$where"TXHULHVVKRXOGQRWEHXVHGXQOHVVVWULFWO\QHFHVVDU\WKH\DUHPXFKVORZHUWKDQUHJXODUTXHULHV(DFKGRFXPHQWKDVWREHFRQYHUWHGIURP%621WRD-DYD6FULSWREMHFWDQGWKHQUXQWKURXJKWKH"$where"H[SUHVVLRQ,QGH[HVFDQQRWEHXVHGWRVDWLVI\D"$where"HLWKHU+HQFH\RXVKRXOGXVH"$where"RQO\ZKHQWKHUHLVQRRWKHUZD\RIGRLQJWKHTXHU\


40/48

> var cursor = db.people.find();> cursor.forEach(function(x) {... print(x.name);... });adammattzak

:KHQ\RXFDOOfindWKHVKHOOGRHVQRWTXHU\WKHGDWDEDVHLPPHGLDWHO\,WZDLWVXQWLO\RXDFWXDOO\VWDUWUHTXHVWLQJUHVXOWVWRVHQGWKHTXHU\ZKLFKDOORZV\RXWRFKDLQDGGLWLRQDORSWLRQVRQWRDTXHU\EHIRUHLWLVSHUIRUPHG$OPRVWHYHU\PHWKRGRQDFXUVRUREMHFWUHWXUQVWKHFXUVRULWVHOIVRWKDW\RXFDQFKDLQWKHPLQDQ\RUGHU)RULQVWDQFHDOORIWKHIROORZLQJDUHHTXLYDOHQW

> var cursor = db.foo.find().sort({"x" : 1}).limit(1).skip(10);> var cursor = db.foo.find().limit(1).sort({"x" : 1}).skip(10);> var cursor = db.foo.find().skip(10).limit(1).sort({"x" : 1});

$WWKLVSRLQWWKHTXHU\KDVQRWEHHQH[HFXWHG\HW$OORIWKHVHIXQFWLRQVPHUHO\EXLOG

WKHTXHU\1RZVXSSRVHZHFDOOWKHIROORZLQJ> cursor.hasNext()

$WWKLVSRLQWWKHTXHU\ZLOOEHVHQWWRWKHVHUYHU7KHVKHOOIHWFKHVWKHILUVWUHVXOWVRUILUVW0%RIUHVXOWVZKLFKHYHULVVPDOOHUDWRQFHVRWKDWWKHQH[WFDOOVWRnextRUhasNextZLOOQRWKDYHWRPDNHWULSVWRWKHVHUYHU$IWHUWKHFOLHQWKDVUXQWKURXJKWKHILUVWVHWRIUHVXOWVWKHVKHOOZLOODJDLQFRQWDFWWKHGDWDEDVHDQGDVNIRUPRUHUHVXOWV7KLVSURFHVVFRQWLQXHVXQWLOWKHFXUVRULVH[KDXVWHGDQGDOOUHVXOWVKDYHEHHQUHWXUQHG

Limits, Skips, and Sorts

7KHPRVWFRPPRQTXHU\RSWLRQVDUHOLPLWLQJWKHQXPEHURIUHVXOWVUHWXUQHGVNLSSLQJDQXPEHURIUHVXOWVDQGVRUWLQJ$OORIWKHVHRSWLRQVPXVWEHDGGHGEHIRUHDTXHU\LVVHQWWRWKHGDWDEDVH

7RVHWDOLPLWFKDLQWKH limitIXQFWLRQRQWR\RXUFDOOWR find)RUH[DPSOHWRRQO\UHWXUQWKUHHUHVXOWVXVHWKLV

> db.c.find().limit(3)

,IWKHUHDUHIHZHUWKDQWKUHHGRFXPHQWVPDWFKLQJ\RXUTXHU\LQWKHFROOHFWLRQRQO\WKHQXPEHURIPDWFKLQJGRFXPHQWVZLOOEHUHWXUQHGlimitVHWVDQXSSHUOLPLWQRWDORZHUOLPLW

skipZRUNVVLPLODUO\WRlimit> db.c.find().skip(3)

7KLVZLOOVNLSWKHILUVWWKUHHPDWFKLQJGRFXPHQWVDQGUHWXUQWKHUHVWRIWKHPDWFKHV,IWKHUHDUHOHVVWKDQWKUHHGRFXPHQWVLQ\RXUFROOHFWLRQLWZLOOQRWUHWXUQDQ\GRFXPHQWV

sort WDNHVDQREMHFWDVHWRINH\YDOXHSDLUVZKHUHWKHNH\VDUHNH\QDPHVDQGWKHYDOXHVDUHWKHVRUWGLUHFWLRQV6RUWGLUHFWLRQFDQEHDVFHQGLQJRUGHVFHQGLQJ,I

Cursors | 57


41/48

PXOWLSOHNH\VDUHJLYHQWKHUHVXOWVZLOOEHVRUWHGLQWKDWRUGHU)RULQVWDQFHWRVRUWWKHUHVXOWVE\"username"DVFHQGLQJDQG"age"GHVFHQGLQJZHGRWKHIROORZLQJ

> db.c.find().sort({username : 1, age : -1})

7KHVHWKUHHPHWKRGVFDQEHFRPELQHG7KLVLVRIWHQKDQG\IRUSDJLQDWLRQ)RUH[DPSOHVXSSRVHWKDW\RXDUHUXQQLQJDQRQOLQHVWRUHDQGVRPHRQHVHDUFKHVIRU PS,I\RX

ZDQWUHVXOWVSHUSDJHVRUWHGE\SULFHIURPKLJKWRORZ\RXFDQGRWKHIROORZLQJ

> db.stock.find({"desc" : "mp3"}).limit(50).sort({"price" : -1})

,IWKH\FOLFN1H[W3DJHWRVHHPRUHUHVXOWV\RXFDQVLPSO\DGGD VNLSWRWKHTXHU\ZKLFKZLOOVNLSRYHUWKHILUVWPDWFKHVZKLFKWKHXVHUDOUHDG\VDZRQSDJH

> db.stock.find({"desc" : "mp3"}).limit(50).skip(50).sort({"price" : -1})

+RZHYHUODUJHVNLSVDUHQRWYHU\SHUIRUPDQWVRWKHUHDUHVXJJHVWLRQVRQDYRLGLQJWKHPLQDPRPHQW

Comparison order

0RQJR'%KDVDKLHUDUFK\DVWRKRZW\SHVFRPSDUH6RPHWLPHV\RXZLOOKDYHDVLQJOHNH\ZLWKPXOWLSOHW\SHVIRULQVWDQFHLQWHJHUVDQGERROHDQVRUVWULQJVDQGQXOOV,I\RXGRDVRUWRQDNH\ZLWKDPL[RIW\SHVWKHUHLVDSUHGHILQHGRUGHUWKDWWKH\ZLOOEHVRUWHGLQ)URPOHDVWWRJUHDWHVWYDOXHWKLVRUGHULQJLVDVIROORZV

0LQLPXPYDOXH

null

1XPEHUVLQWHJHUVORQJVGRXEOHV

6WULQJV

2EMHFWGRFXPHQW $UUD\

%LQDU\GDWD

2EMHFW,'

%RROHDQ

'DWH

7LPHVWDPS

5HJXODUH[SUHVVLRQ

0D[LPXPYDOXH

Avoiding Large Skips8VLQJskipIRUDVPDOOQXPEHURIGRFXPHQWVLVILQH)RUDODUJHQXPEHURIUHVXOWVskipFDQEHVORZWKLVLVWUXHLQQHDUO\HYHU\GDWDEDVHQRWMXVW0RQJR'%DQGVKRXOGEHDYRLGHG8VXDOO\\RXFDQEXLOGFULWHULDLQWR WKH GRFXPHQWVWKHPVHOYHVWRDYRLG



42/48

KDYLQJWRGRODUJHVNLSVRU\RXFDQFDOFXODWHWKHQH[WTXHU\EDVHGRQWKHUHVXOWIURPWKHSUHYLRXVRQH

Paginating results without skip

7KHHDVLHVWZD\WRGRSDJLQDWLRQLVWRUHWXUQWKHILUVWSDJHRIUHVXOWVXVLQJOLPLWDQG

WKHQUHWXUQHDFKVXEVHTXHQWSDJHDVDQRIIVHWIURPWKHEHJLQQLQJ> // do not use: slow for large skips> var page1 = db.foo.find(criteria).limit(100)> var page2 = db.foo.find(criteria).skip(100).limit(100)> var page3 = db.foo.find(criteria).skip(200).limit(100)...

+RZHYHUGHSHQGLQJRQ\RXUTXHU\\RXFDQXVXDOO\ILQGDZD\WRSDJLQDWHZLWKRXWskipV)RUH[DPSOHVXSSRVHZHZDQWWRGLVSOD\GRFXPHQWVLQGHVFHQGLQJRUGHUEDVHGRQ"date":HFDQJHWWKHILUVWSDJHRIUHVXOWVZLWKWKHIROORZLQJ

> var page1 = db.foo.find().sort({"date" : -1}).limit(100)

7KHQZHFDQXVHWKH"date"YDOXHRIWKHODVWGRFXPHQWDVWKHFULWHULDIRUIHWFKLQJWKHQH[WSDJH

var latest = null;

// display first pagewhile (page1.hasNext()) {

latest = page1.next();display(latest);

}

// get next pagevar page2 = db.foo.find({"date" : {"$gt" : latest.date}});

page2.sort({"date" : -1}).limit(100);

1RZWKHTXHU\GRHVQRWQHHGWRLQFOXGHDskip

Finding a random document

2QHIDLUO\FRPPRQSUREOHPLVKRZWRJHWDUDQGRPGRFXPHQWIURPDFROOHFWLRQ7KHQDLYHDQGVORZVROXWLRQLVWRFRXQWWKHQXPEHURIGRFXPHQWVDQGWKHQGRD findVNLSSLQJDUDQGRPQXPEHURIGRFXPHQWVEHWZHHQDQGWKHVL]HRIWKHFROOHFWLRQ

> // do not use> var total = db.foo.count()> var random = Math.floor(Math.random()*total)> db.foo.find().skip(random).limit(1)

,WLVDFWXDOO\KLJKO\LQHIILFLHQWWRJHWDUDQGRPHOHPHQWWKLVZD\\RXKDYHWRGRDFRXQWZKLFKFDQEHH[SHQVLYHLI\RXDUHXVLQJFULWHULDDQGVNLSSLQJODUJHQXPEHUVRIHOHPHQWVFDQEHWLPHFRQVXPLQJ

,WWDNHVDOLWWOHIRUHWKRXJKWEXWLI\RXNQRZ\RXOOEHORRNLQJXSDUDQGRPHOHPHQWRQDFROOHFWLRQWKHUHVDPXFKPRUHHIILFLHQWZD\WRGRVR7KHWULFNLVWRDGGDQH[WUD

Cursors | 59


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UDQGRPNH\WRHDFKGRFXPHQWZKHQLWLVLQVHUWHG)RULQVWDQFHLIZHUHXVLQJWKHVKHOOZHFRXOGXVHWKHMath.random()IXQFWLRQZKLFKFUHDWHVDUDQGRPQXPEHUEHWZHHQDQG

> db.people.insert({"name" : "joe", "random" : Math.random()})> db.people.insert({"name" : "john", "random" : Math.random()})> db.people.insert({"name" : "jim", "random" : Math.random()})

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> var random = Math.random()> result = db.foo.findOne({"random" : {"$gt" : random}})

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> if (result == null) {... result = db.foo.findOne({"random" : {"$lt" : random}})

... }

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> db.people.ensureIndex({"profession" : 1, "state" : 1, "random" : 1})

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Advanced Query Options7KHUHDUHWZRW\SHVRITXHULHV ZUDSSHGDQGSODLQ$SODLQTXHU\LVVRPHWKLQJOLNHWKLV

> var cursor = db.foo.find({"foo" : "bar"})

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> var cursor = db.foo.find({"foo" : "bar"}).sort({"x" : 1})

,QVWHDGRIVHQGLQJ{"foo" : "bar"}WRWKHGDWDEDVHDVWKHTXHU\WKHTXHU\JHWVZUDSSHG

LQDODUJHUGRFXPHQW7KHVKHOOFRQYHUWVWKHTXHU\IURP{"foo" : "bar"}WR{"$query" :{"foo" : "bar"}, "$orderby" : {"x" : 1}}

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$maxscan : integer6SHFLI\WKHPD[LPXPQXPEHURIGRFXPHQWVWKDWVKRXOGEHVFDQQHGIRUWKHTXHU\



44/48

$min : document6WDUWFULWHULDIRUTXHU\LQJ

$max : document(QGFULWHULDIRUTXHU\LQJ

$hint : document

7HOOWKHVHUYHUZKLFKLQGH[WRXVHIRUWKHTXHU\$explain : boolean

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$snapshot : boolean(QVXUHWKDWWKHTXHU\VUHVXOWVZLOOEHDFRQVLVWHQWVQDSVKRWIURPWKHSRLQWLQWLPHZKHQWKHTXHU\ZDVH[HFXWHG6HHWKHQH[WVHFWLRQIRUGHWDLOV

Getting Consistent Results$IDLUO\FRPPRQZD\RISURFHVVLQJGDWDLVWRSXOOLWRXWRI0RQJR'%FKDQJHLWLQVRPHZD\DQGWKHQVDYHLWDJDLQ

cursor = db.foo.find();

while (cursor.hasNext()) {var doc = cursor.next();doc = process(doc);db.foo.save(doc);

}

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45/48

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)LJXUH$FXUVRUPD\UHWXUQWKHVHUHORFDWHGGRFXPHQWVDJDLQLQDODWHUEDWFK

7KHVROXWLRQWRWKLVSUREOHPLVWRVQDSVKRW\RXUTXHU\,I\RXDGGWKH"$snapshot"RSWLRQWKHTXHU\ZLOOEHUXQDJDLQVWDQXQFKDQJLQJYLHZRIWKHFROOHFWLRQ$OOTXHULHVWKDWUHWXUQDVLQJOHEDWFKRIUHVXOWVDUHHIIHFWLYHO\VQDSVKRWWHG,QFRQVLVWHQFLHVDULVH

)LJXUH$QHQODUJHGGRFXPHQWPD\QRWILWZKHUHLWGLGEHIRUH

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46/48

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Cursor Internals

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2QWKHVHUYHUVLGHDFXUVRUWDNHVXSPHPRU\DQGUHVRXUFHV2QFHDFXUVRUUXQVRXWRIUHVXOWVRUWKHFOLHQWVHQGVDPHVVDJHWHOOLQJLWWRGLHWKHGDWDEDVHFDQIUHHWKHUHVRXUFHVLWZDVXVLQJ)UHHLQJWKHVHUHVRXUFHVOHWVWKHGDWDEDVHXVHWKHPIRURWKHUWKLQJVZKLFKLVJRRGVRZHZDQWWRPDNHVXUHWKDWFXUVRUVFDQEHIUHHGTXLFNO\ZLWKLQUHDVRQ

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Cursor Internals | 63


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