查询（mongodb权威指南第4章）

• 使用find或者findOne函数和查询文档对数据库执行查询
• 使用$条件查询实现范围、集合包含、不等式和其他查询
• 有些查询用查询文档，甚至$条件语句都不能表达，对于这种复杂的查询，可以用$where 子句，用强大的javasript来表达
• 查询将会返回一个数据库游标，游标只有在你需要的时候才会惰性的批量返回文档
• 还有很多针对游标执行的元操作，包括忽略一定数量的结果，或者限定返回结果的数量，还有对结果排序

4.1 find简介

D:\java\mongodb-win32-i386-2.2.3\bin>mongo MongoDB shell version: 2.2.3 connecting to: test > show dbs; local   (empty) test    0.125GB > use test; switched to db test > db.foo.find() { "_id" : ObjectId("5149af43ad11c9803e1781ea"), "bar" : "baz" } { "_id" : ObjectId("5149d1ffad11c9803e1781eb"), "xx" : 2 } > db.foo.insert({"name":"king","age":20}) > db.foo.insert({"name":"king1","age":25}) > db.foo.insert({"name":"king2","age":21}) > db.foo.find() { "_id" : ObjectId("5149af43ad11c9803e1781ea"), "bar" : "baz" } { "_id" : ObjectId("5149d1ffad11c9803e1781eb"), "xx" : 2 } { "_id" : ObjectId("514c7dce127bab4493992956"), "name" : "king", "age" : 20 } { "_id" : ObjectId("514c7dda127bab4493992957"), "name" : "king1", "age" : 25 } { "_id" : ObjectId("514c7de3127bab4493992958"), "name" : "king2", "age" : 21 } > db.foo.find({"name":king}) Fri Mar 22 23:51:29 ReferenceError: king is not defined (shell):1 > db.foo.find({"name":"king"}) { "_id" : ObjectId("514c7dce127bab4493992956"), "name" : "king", "age" : 20 } > db.foo.find({"name":"king","age":20}) { "_id" : ObjectId("514c7dce127bab4493992956"), "name" : "king", "age" : 20 } >

  可以通过向查询文档加入多个键值对组合查询条件，解释为and

   空的查询文档{}会匹配集合的所有文档，要是不指定，默认就是{}

  4.1.1 指定返回的键

     可以通过find或者findOne的第二个参数指定想要的键。

> db.foo.find({},{"name":1})        只返回name,_id总是被返回，即便没有指定也一样 ObjectId("5149af43ad11c9803e1781ea") } { "_id" : ObjectId("5149d1ffad11c9803e1781eb") } { "_id" : ObjectId("514c7dce127bab4493992956"), "name" : "king" } { "_id" : ObjectId("514c7dda127bab4493992957"), "name" : "king1" } { "_id" : ObjectId("514c7de3127bab4493992958"), "name" : "king2" } > db.foo.find({},{"name":0})    剔除查询结果中的某个键值对 "_id" : ObjectId("5149af43ad11c9803e1781ea"), "bar" : "baz" } { "_id" : ObjectId("5149d1ffad11c9803e1781eb"), "xx" : 2 } { "_id" : ObjectId("514c7dce127bab4493992956"), "age" : 20 } { "_id" : ObjectId("514c7dda127bab4493992957"), "age" : 25 } { "_id" : ObjectId("514c7de3127bab4493992958"), "age" : 21 } > db.foo.find({},{"name":1,"_id":0})  防止返回_id } { "name" : "king" } { "name" : "king1" } { "name" : "king2" } >

    4.1.2 限制

        数据库所关心的查询文档必须是常量。

4.2 查询条件

        范围、OR子句和取反

     4.2.1 查询条件

        比较操作符：“$lt”，“$lte","$gt","$gte"  "$ne

                            <     <=   >      >=      !=

  db.user.find({"birthday":{"$lt":start}})

start=new Date("01/01/2009")

> db.foo.find() { "_id" : ObjectId("5149af43ad11c9803e1781ea"), "bar" : "baz" } { "_id" : ObjectId("5149d1ffad11c9803e1781eb"), "xx" : 2 } { "_id" : ObjectId("514c7dce127bab4493992956"), "name" : "king", "age" : 20 } { "_id" : ObjectId("514c7dda127bab4493992957"), "name" : "king1", "age" : 25 } { "_id" : ObjectId("514c7de3127bab4493992958"), "name" : "king2", "age" : 21 } > db.foo.find({"age":{"$gte":21,"$lte":25}}) { "_id" : ObjectId("514c7dda127bab4493992957"), "name" : "king1", "age" : 25 } { "_id" : ObjectId("514c7de3127bab4493992958"), "name" : "king2", "age" : 21 } > db.foo.find({"name":{"$ne":"king"}}) { "_id" : ObjectId("5149af43ad11c9803e1781ea"), "bar" : "baz" } { "_id" : ObjectId("5149d1ffad11c9803e1781eb"), "xx" : 2 } { "_id" : ObjectId("514c7dda127bab4493992957"), "name" : "king1", "age" : 25 } { "_id" : ObjectId("514c7de3127bab4493992958"), "name" : "king2", "age" : 21 } > db.foo.find({"age":{"$lte":25}}) { "_id" : ObjectId("514c7dce127bab4493992956"), "name" : "king", "age" : 20 } { "_id" : ObjectId("514c7dda127bab4493992957"), "name" : "king1", "age" : 25 } { "_id" : ObjectId("514c7de3127bab4493992958"), "name" : "king2", "age" : 21 }

   4.2.2 OR查询

      mongodb中有两种方式进行OR查询。

      "$in"可以用来查询一个键的多个值。  "$nin"  针对单个键做OR查询

> db.foo.find({"age":{"$in":[21,25]}}) { "_id" : ObjectId("514c7dda127bab4493992957"), "name" : "king1", "age" : 25 } { "_id" : ObjectId("514c7de3127bab4493992958"), "name" : "king2", "age" : 21 } > db.foo.insert({"name":234,"age":30}) > db.foo.find("name":{"$in":["king",234]}) Sat Mar 23 00:25:25 SyntaxError: missing ) after argument list (shell):1 > db.foo.find({"name":{"$in":["king",234]}}) { "_id" : ObjectId("514c7dce127bab4493992956"), "name" : "king", "age" : 20 } { "_id" : ObjectId("514c85c1127bab4493992959"), "name" : 234, "age" : 30 } > db.foo.find({"name":"king"}) { "_id" : ObjectId("514c7dce127bab4493992956"), "name" : "king", "age" : 20 } > db.foo.find({"name":{"$in":["king"]}}) { "_id" : ObjectId("514c7dce127bab4493992956"), "name" : "king", "age" : 20 }

> db.foo.find({"name":{"$nin":"king"}}) error: { "$err" : "$nin needs an array", "code" : 13277 } > db.foo.find({"name":{"$nin":["king"]}}) { "_id" : ObjectId("5149af43ad11c9803e1781ea"), "bar" : "baz" } { "_id" : ObjectId("5149d1ffad11c9803e1781eb"), "xx" : 2 } { "_id" : ObjectId("514c7dda127bab4493992957"), "name" : "king1", "age" : 25 } { "_id" : ObjectId("514c7de3127bab4493992958"), "name" : "king2", "age" : 21 } { "_id" : ObjectId("514c85c1127bab4493992959"), "name" : 234, "age" : 30 }

 

      "$or"完成多个键值的任意给定值。接受一个包含所有可能条件的数组作为参数

> db.foo.find({"$or":[{"name":"king"},{"age":20}]}) { "_id" : ObjectId("514c7dce127bab4493992956"), "name" : "king", "age" : 20 } > db.foo.find({"$or":[{"name":{"$in":["king","king1"]}}]}) { "_id" : ObjectId("514c7dce127bab4493992956"), "name" : "king", "age" : 20 } { "_id" : ObjectId("514c7dda127bab4493992957"), "name" : "king1", "age" : 25 }

     使用普通的AND查询时，尽可能用最少的条件来限定结果的范围

     OR型的相反：第一个条件进啊可能匹配更多的文档，这样最有效。

  4.2.3 $not

     这是个元条件句，即可以用在任何其他条件之上。

> db.foo.find({"age":{"$mod":[5,1]}}) { "_id" : ObjectId("514c7de3127bab4493992958"), "name" : "king2", "age" : 21 } > db.foo.find({"age":{"$not":{"$mod":[5,1]}}}) { "_id" : ObjectId("5149af43ad11c9803e1781ea"), "bar" : "baz" } { "_id" : ObjectId("5149d1ffad11c9803e1781eb"), "xx" : 2 } { "_id" : ObjectId("514c7dce127bab4493992956"), "name" : "king", "age" : 20 } { "_id" : ObjectId("514c7dda127bab4493992957"), "name" : "king1", "age" : 25 } { "_id" : ObjectId("514c85c1127bab4493992959"), "name" : 234, "age" : 30 }

  4.2.4 条件句的规则

4.3 特定与类型的查询

     4.3.1 null

•          匹配自身
• 匹配不存在的
• 如果之匹配键值为null的文档，纪要检查改建的值是否为null,还要通过"$exists"条件判定改建已经存在

> db.foo.insert({"name":null,"age":28}) > db.foo.find() { "_id" : ObjectId("5149af43ad11c9803e1781ea"), "bar" : "baz" } { "_id" : ObjectId("5149d1ffad11c9803e1781eb"), "xx" : 2 } { "_id" : ObjectId("514c7dce127bab4493992956"), "name" : "king", "age" : 20 } { "_id" : ObjectId("514c7dda127bab4493992957"), "name" : "king1", "age" : 25 } { "_id" : ObjectId("514c7de3127bab4493992958"), "name" : "king2", "age" : 21 } { "_id" : ObjectId("514c85c1127bab4493992959"), "name" : 234, "age" : 30 } { "_id" : ObjectId("514d0c6be30a115bf216e111"), "name" : null, "age" : 28 } > db.foo.find({"name":null}) { "_id" : ObjectId("5149af43ad11c9803e1781ea"), "bar" : "baz" } { "_id" : ObjectId("5149d1ffad11c9803e1781eb"), "xx" : 2 } { "_id" : ObjectId("514d0c6be30a115bf216e111"), "name" : null, "age" : 28 } > db.foo.find({"name":{"$in":[null],"$exists:true"}}) Sat Mar 23 10:01:50 SyntaxError: missing : after property id (shell):1 > db.foo.find({"name":{"$in":[null],"$exists":true}}) { "_id" : ObjectId("514d0c6be30a115bf216e111"), "name" : null, "age" : 28 } >

     4.3.2 正则表达式

     4.3.3 查询数组

        绝大多数情况下可以这样理解：每一个元素都是整个键的值

> db.fruit.insert({"fruit":["apple","banana","peach"]}) > db.fruit.insert({"fruit":["apple","banana","peach"]}) > db.fruit.find() { "_id" : ObjectId("514d0f6ae30a115bf216e112"), "fruit" : [ "apple", "banana", " peach" ] } { "_id" : ObjectId("514d0f72e30a115bf216e113"), "fruit" : [ "apple", "banana", " peach" ] } > db.fruit.find({"fruit":"apple"}) { "_id" : ObjectId("514d0f6ae30a115bf216e112"), "fruit" : [ "apple", "banana", " peach" ] } { "_id" : ObjectId("514d0f72e30a115bf216e113"), "fruit" : [ "apple", "banana", " peach" ] }

  这个查询相当于我们用了一个如下的文档（不合法的）进行的查询：

  {”fruit“：”apple","fruit":"banana"}

• $all  需要通过多个元素来匹配数组

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

    也可以使用完整的数组精确地匹配。但是，精确匹配对于有缺少或者冗余元素的情况下就不灵了。

> db.fruit.find({"fruit":["apple","banana","peach"]}) { "_id" : 1, "fruit" : [ "apple", "banana", "peach" ] } > db.fruit.find({"fruit":["apple","banana"]}) > db.fruit.find({"fruit":["banana","apple","peach"]}) >

    要想查询数组指定位置的元素，需要使用key.index语法制定下标，下标从0开始

> db.fruit.find({"fruit.2":"peach"}) { "_id" : 1, "fruit" : [ "apple", "banana", "peach" ] } >

•    $size 查询指定长度的数组

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

 

 

 

• $slice find的第二个参数是可选的，可以指定返回哪些键，$slice返回数组的一个子集合

       可以接受偏移量和要返回的元素数量，来返回中间的结果

       除非特别声明，返回文档中的所有键

      

 

  4.3.4查询内嵌文档

     有两种发方法：查询整个文档或者只针对其键值对进行查询

    查询整个内嵌文档与普通查询完全相同：

  

4.4 $where 查询

    用它可以执行任意javascript作为查询的一部分，是得查询几乎能做任何事情。

   最典型的应用就是比较文档中的两个键的值是否相等。

   避免使用。

4.5 游标

  

4.6 游标内幕