MongoDB常用操作---查询find方法

(来源：MongoDB常用操作一查询find方法db.collection_name.find())

db.collection_name.find()

1. 基本查询
   db.users.find({}, {'name' : 1, 'skills' : 1});
   where name = 'hurry';
   第一个{} 放where条件 第二个{} 指定那些列显示和不显示 （0表示不显示 1表示显示)

2. and查询
   db.users.find({'name' : 'hurry', 'age' : 18});
   where name = 'hurry' and age = 18;

3. or查询
   db.users.find({ '$or' : [{'name' : 'hurry'}, {'age' : 18}]});
   where name = 'hurry' or age = 18;

4. 比较查询 <, <=, >, >= ($lt, $lte, $gt, $gte )
   db.users.find({'age' : {'$gte' : 20, '$lte' : 30}});
   where age >= 20 and age <= 30;

5. in, not in ($in, $nin)
   db.users.find({'age' : {'$in' : [10, 22, 26]}});
   where age in (10, 22, 26);

6. 匹配null
   db.users.find({'age' : null);
   where age is null;

7. like (mongoDB 支持正则表达式)
   db.users.find({name:/hurry/});
   where name like "%hurry%";
   db.users.find({name:/^hurry/});
   where name like "hurry%";

8. 使用distinct
   db.users.distinct('name');
   select distinct (name) from users;

9. 使用count
   db.users.find({"price":"1"}).count()
   select count(*) from users where price = "1";

10. 数组查询（mongo特色）

    $all

    db.users.find({"price": {'$all' : ['3.1','4.1']}})
    查询price是 ['3.1','4.1']

    $size

    db.users.find({"price":{$size:2}})
    查询price是 二维数组

    $slice

    db.users.find({},{"price":{$slice :3}})
    设置返回的price的长度
    假设 price 为 ['3.1','4.1','5.1']
    db.users.find({},{"price":{$slice :3}}) 返回 ['3.1','4.1','5.1']
    db.users.find({},{"price":{$slice :2}}) 返回 ['3.1','4.1']
    db.users.find({},{"price":{$slice :1}}) 返回 ['3.1']

    可以设置2个整数 第一个是skipNum 第二个是返回的长度
    db.users.find({},{"price":{$slice :[1,1]}}) 返回 ['4.1']
    如果skip大于等于price的长度，则返回[]

11. $where查询

    $gt:大于
    $lt:小于
    $gte:大于或等于
    $lte:小于或等于
    db.collection.find({ "field" : { $gt: value1, $lt: value2 } } ); // value1 < field < value

    不等于 $ne
    db.things.find( { x : { $ne : 3 } } );

    in 和 not in ($in $nin)
    db.collection.find( { "field" : { $in : array } } );

    取模运算$mod
    db.things.find( "this.a % 10 == 1")
    db.things.find( { a : { $mod : [ 10 , 1 ] } } )

    $exists用来判断一个元素是否存在
    db.things.find( { a : { $exists : true } } ); // 如果存在元素a,就返回
    db.things.find( { a : { $exists : false } } ); // 如果不存在元素a，就返回

    $elemMatch

    The $elemMatch operator limits the contents of an array field from the query results to contain only the first element matching the $elemMatch condition.
    限制返回内容，并且只返回第一个匹配的数据

    {
     _id: 1,
     zipcode: "63109",
     students: [
      { name: "john", school: 102, age: 10 },
      { name: "jess", school: 102, age: 11 },
      { name: "jeff", school: 108, age: 15 }
       ]
    }
    {
     _id: 2,
     zipcode: "63110",
     students: [
                  { name: "ajax", school: 100, age: 7 },
                  { name: "achilles", school: 100, age: 8 },
               ]
    }
    {
     _id: 3,
     zipcode: "63109",
     students: [
                  { name: "ajax", school: 100, age: 7 },
                  { name: "achilles", school: 100, age: 8 },
               ]
    }
    {
     _id: 4,
     zipcode: "63109",
     students: [
                  { name: "barney", school: 102, age: 7 },
                  { name: "ruth", school: 102, age: 16 },
               ]
    }
    

    查询语句：db.schools.find( { zipcode: "63109" },
    { students: { $elemMatch: { school: 102 } } } )

    返回结果

    { "_id" : 1, "students" : [ { "name" : "john", "school" : 102, "age" : 10 } ] }
    { "_id" : 3 }
    { "_id" : 4, "students" : [ { "name" : "barney", "school" : 102, "age" : 7 } ] }
    

12. 正则表达式

    db.things.find({"price":/4.1/})
    返回price数组里面有4.1的数据
    db.things.find({"productId":/6{1,6}/})
    返回productId值为6到666666的数据