mongo-查询（5）——查询数组

查询数组。此时你可能会使用到$all、$size。

> db.tianyc04.find()
{ "_id" : 1, "fruit" : [ "apple", "banana", "peach" ] }
{ "_id" : 2, "fruit" : [ "apple", "orange", "peach" ] }
{ "_id" : 3, "fruit" : [ "orange", "banana", "peach" ] }

#通过全匹配，查询第一行
> db.tianyc04.find({fruit:["apple", "banana", "peach"]})
{ "_id" : 1, "fruit" : [ "apple", "banana", "peach" ] }

#如果将数组中的顺序颠倒，则第一行就匹配不上了。此时可以使用$all

> db.tianyc04.find({fruit:["apple", "peach", "banana"]})

> db.tianyc04.find({fruit:{$all:["apple", "peach", "banana"]}})
{ "_id" : 1, "fruit" : [ "apple", "banana", "peach" ] }

#也可以只输入一个元素进行查询

 > db.tianyc04.find({fruit:'apple'})

{ "_id" : 1, "fruit" : [ "apple", "banana", "peach" ] }
{ "_id" : 2, "fruit" : [ "apple", "orange", "peach" ] }

#如果这个元素变成了数组，mongo就会进行精确匹配。此时你可能需要使用$all进行模糊匹配：

> db.tianyc04.find({fruit:['apple']})

> db.tianyc04.find({fruit:{$all:['apple']}})
{ "_id" : 1, "fruit" : [ "apple", "banana", "peach" ] }
{ "_id" : 2, "fruit" : [ "apple", "orange", "peach" ] }

#还可以按照数组中指定位置的元素进行查询，注意数组下标的起始编号是0。

> db.tianyc04.find()
{ "_id" : 1, "fruit" : [ "apple", "banana", "peach" ] }
{ "_id" : 2, "fruit" : [ "apple", "orange", "peach" ] }
{ "_id" : 3, "fruit" : [ "orange", "banana", "peach" ] }
> db.tianyc04.find({'fruit.1':'orange'})
{ "_id" : 2, "fruit" : [ "apple", "orange", "peach" ] }

#可以按照数组长度进行查询，只查询数组长度为x的文档。

> db.tianyc04.find()
{ "_id" : 1, "fruit" : [ "apple", "banana", "peach" ] }
{ "_id" : 2, "fruit" : [ "apple", "orange", "peach" ] }
{ "_id" : 3, "fruit" : [ "orange", "banana", "peach" ] }
{ "_id" : 4, "fruit" : [ "apple" ] }
> db.tianyc04.find({fruit:{$size:3}})
{ "_id" : 1, "fruit" : [ "apple", "banana", "peach" ] }
{ "_id" : 2, "fruit" : [ "apple", "orange", "peach" ] }
{ "_id" : 3, "fruit" : [ "orange", "banana", "peach" ] }
> db.tianyc04.find({fruit:{$size:1}})
{ "_id" : 4, "fruit" : [ "apple" ] }
>