Mongodb最大的功能之一就是它支持動態(tài)查詢，就跟傳統(tǒng)的關(guān)系型數(shù)據(jù)庫查詢一樣，但是它的查詢來的更靈活。
一、 Query Expression Objects：查詢表達式對象
查詢表達式文檔也是一個BSON結(jié)構(gòu)的文檔，例如，我們可以用下面的查詢語句來查詢集合中的所有記錄：
db.users.find({})
這里，表達式對象是一個空文檔，在查詢的時候去去匹配所有的記錄。再看：
這里，我們將會查詢出所有“l(fā)ast_name”屬性值為“Smith”的文檔記錄。
二、查詢選項
除了查詢表達式意外，Mongodb還支持一些額外的參數(shù)選項。例如，我們可能僅僅只想返回某些特定的字段值：
注： _id字段始終都會被返回，哪怕沒有明確指定
三、查詢條件
1) <, <=, >, >=
// 大于: field > value db.collection.find({ "field" : { $gt: value } } ); //小于：field < value db.collection.find({ "field" : { $lt: value } } ); //大于等于: field >= value db.collection.find({ "field" : { $gte: value } } ); //小于等于：field<=value db.collection.find({ "field" : { $lte: value } } ); 2) $all
$all操作類似$in操作，但是不同的是，$all操作要求數(shù)組里面的值全部被包含在返回的記錄里面，如：
> use test; switched to db test > db.things.insert({a:[1,2,3]}); > db.things.find(); { "_id" : ObjectId("4de73360059e7f4bdf907cfe"), "a" : [ 1, 2, 3 ] } > db.things.find({a:{$all:[2,3]}}); { "_id" : ObjectId("4de73360059e7f4bdf907cfe"), "a" : [ 1, 2, 3 ] } > db.things.find({a:{$all:[1,2,3]}}); { "_id" : ObjectId("4de73360059e7f4bdf907cfe"), "a" : [ 1, 2, 3 ] } > db.things.find({a:{$all:[1]}}); { "_id" : ObjectId("4de73360059e7f4bdf907cfe"), "a" : [ 1, 2, 3 ] } > db.things.find({a:{$all:[1,2,3,4]}});3) $exists
$exists操作檢查一個字段是否存在，如：
> for(var i=0;i<1000;i++) db.user.save({_id:i,name:'user'+i,userid:i,age:20}); //包含userid > db.user.find({userid:{$exists:true}}).limit(5); { "_id" : 0, "name" : "user0", "userid" : 0, "age" : 20 } { "_id" : 1, "name" : "user1", "userid" : 1, "age" : 20 } { "_id" : 2, "name" : "user2", "userid" : 2, "age" : 20 } { "_id" : 3, "name" : "user3", "userid" : 3, "age" : 20 } { "_id" : 4, "name" : "user4", "userid" : 4, "age" : 20 } //不包含sex字段 > db.user.find({sex:{$exists:false}}).limit(5); 4) $mod
$mod操作可以讓我們簡單的進行取模操作，而不需要用到where子句，如：
//where子句 > db.user.find("this._id%10==1").limit(5); { "_id" : 1, "name" : "user1", "userid" : 1, "age" : 20 } { "_id" : 11, "name" : "user11", "userid" : 11, "age" : 20 } { "_id" : 21, "name" : "user21", "userid" : 21, "age" : 20 } { "_id" : 31, "name" : "user31", "userid" : 31, "age" : 20 } { "_id" : 41, "name" : "user41", "userid" : 41, "age" : 20 } //$mod操作 > db.user.find({_id:{$mod:[10,1]}}).limit(5); { "_id" : 1, "name" : "user1", "userid" : 1, "age" : 20 } { "_id" : 11, "name" : "user11", "userid" : 11, "age" : 20 } { "_id" : 21, "name" : "user21", "userid" : 21, "age" : 20 } { "_id" : 31, "name" : "user31", "userid" : 31, "age" : 20 } { "_id" : 41, "name" : "user41", "userid" : 41, "age" : 20 } 5) $ne
$ne意思是not equal，不等于，不用多說，看例子：
> db.user.find().limit(5); { "_id" : 0, "name" : "user0", "userid" : 0, "age" : 20 } { "_id" : 1, "name" : "user1", "userid" : 1, "age" : 20 } { "_id" : 2, "name" : "user2", "userid" : 2, "age" : 20 } { "_id" : 3, "name" : "user3", "userid" : 3, "age" : 20 } { "_id" : 4, "name" : "user4", "userid" : 4, "age" : 20 } > db.user.find({_id:{$ne:0}}).limit(5); { "_id" : 1, "name" : "user1", "userid" : 1, "age" : 20 } { "_id" : 2, "name" : "user2", "userid" : 2, "age" : 20 } { "_id" : 3, "name" : "user3", "userid" : 3, "age" : 20 } { "_id" : 4, "name" : "user4", "userid" : 4, "age" : 20 } { "_id" : 5, "name" : "user5", "userid" : 5, "age" : 20 }6) $in
$in操作類似于傳統(tǒng)關(guān)系數(shù)據(jù)庫中的IN，看例子：
//數(shù)據(jù)庫中有所有數(shù)組對應(yīng)的記錄 > db.user.find({_id:{$in:[2,3,4,5,6]}}).limit(5); { "_id" : 2, "name" : "user2", "userid" : 2, "age" : 20 } { "_id" : 3, "name" : "user3", "userid" : 3, "age" : 20 } { "_id" : 4, "name" : "user4", "userid" : 4, "age" : 20 } { "_id" : 5, "name" : "user5", "userid" : 5, "age" : 20 } { "_id" : 6, "name" : "user6", "userid" : 6, "age" : 20 } //因為數(shù)據(jù)庫中沒有_id=1111的記錄 > db.user.find({_id:{$in:[2,3,4,5,1111]}}).limit(5); { "_id" : 2, "name" : "user2", "userid" : 2, "age" : 20 } { "_id" : 3, "name" : "user3", "userid" : 3, "age" : 20 } { "_id" : 4, "name" : "user4", "userid" : 4, "age" : 20 } { "_id" : 5, "name" : "user5", "userid" : 5, "age" : 20 }7) $nin
$nin跟$in操作相反，看例子：
//扣掉_id=1/2/3/4的記錄 > db.user.find({_id:{$nin:[1,2,3,4]}}).limit(5); { "_id" : 0, "name" : "user0", "userid" : 0, "age" : 20 } { "_id" : 5, "name" : "user5", "userid" : 5, "age" : 20 } { "_id" : 6, "name" : "user6", "userid" : 6, "age" : 20 } { "_id" : 7, "name" : "user7", "userid" : 7, "age" : 20 } { "_id" : 8, "name" : "user8", "userid" : 8, "age" : 20 } 8) $nor、$or
$nor跟$or相反，不好解釋，看例子：
> db.user.find({$nor:[{_id:2},{name:'user3'},{userid:4}]}).limit(5); { "_id" : 0, "name" : "user0", "userid" : 0, "age" : 20 } { "_id" : 1, "name" : "user1", "userid" : 1, "age" : 20 } { "_id" : 5, "name" : "user5", "userid" : 5, "age" : 20 } { "_id" : 6, "name" : "user6", "userid" : 6, "age" : 20 } { "_id" : 7, "name" : "user7", "userid" : 7, "age" : 20 }> db.user.find({$or:[{_id:2},{name:'user3'},{userid:4}]}).limit(5); { "_id" : 2, "name" : "user2", "userid" : 2, "age" : 20 } { "_id" : 3, "name" : "user3", "userid" : 3, "age" : 20 } { "_id" : 4, "name" : "user4", "userid" : 4, "age" : 20 } 以上所述就是本文的全部內(nèi)容了，希望大家能夠喜歡。
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