Node.js数据库交互：LevelDB、Redis与CouchDB探索

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$npminstalllevel-sublevel--save

We’llalsobeneedingtogeneraterandomuniqueIDs,solet’stakethechancetoinstalthe

cuidNPMmodule:

$npminstallcuid--save

Wecannowuselevelandlevel-subleveltocreatethetwosub-databases–oneforholding

userrecordsandanotherforholdingusermessages:

sublevels.js:

varlevel=require('level');

varpath=require('path');

varsublevel=require('level-sublevel');

vardbPath=process.env.DB_PATH||path.join(__dirname,'sublevels');

vardb=sublevel(level(dbPath,{

valueEncoding:'json'

}));

exports.base=db;

exports.users=db.sublevel('users');

exports.messages=db.sublevel('messages');

Herewe’rewrappingthedatabasereturnedbylevelwithsublevel,storingitina

temporaryvariablenameddb.Wethencreatethetwosub-databasesbycalling

db.sublevel('<DATABASENAME>'),oneforusersandanotherformessages.

Nowwecanusethissublevelsmoduletopopulatethedatabase:

sublevels_populate.js:

varcuid=require('cuid');

vardb=require('./sublevels');

varuser={

name:'John',

email:'user1@example.com'

};

db.users.put(user.email,user,function(){

for(vari=1;i<=20;i++){

varuserMessages=db.messages.sublevel(user.email);

userMessages.put(cuid(),{

from:'user'+i+'@example.com',

to:'user1@example.com',

subject:'Hey!',

body:'heythere,howyoudoing?'

});

}

});

Herewe’recreatingauserrecord,andthencreating20messagesaddressedtothem.You

canseehowwecancreateasublevelinsideanothersublevel:we’restoringtheuser

messagesinasub-databasenamedaftertheuseremailinsidethemessagessub-database.

YoumayalsohavenoticedthateachmessagehasauniqueIDgiventousbythecuid

module.

Let’scallourscript:

$nodesublevels_populate

Nowwecancreateascripttoqueryourdatabase:

sublevels_query.js:

vardb=require('./sublevels');

varemail=process.argv[2];

db.users.get(email,function(err,user){

if(err){

throwerr;

}

console.log('User:%j',user);

varuserMessages=db.messages.sublevel(email);

userMessages.createValueStream().on('data',function(message){

console.log('Message:%j',message);

})

.once('end',function(){

console.log('nomoremessages');

});

});

Wecannowtestthisscript,usingittoqueryouruser:

$nodesublevels_query.jsuser1@example.com

User:{"name":"John","email":"user1@example.com"}

Message:{"from":"user1@example.com","to":"user1@example.com","subject":"Hey!","\