mongodb查询

1.查询单条记录

> db.choice.findOne()

2.查询时指定查询条件

> db.choice.find({"_id":"005a38d5"})

默认{}查询全部

指定返回列

> db.choice.find({"_id":"005a38d5"},{"title":1,"results":1})
{ "_id" : "005a38d5", "title" : "While some maintain that the recent proliferati
on of uncredited web sources will have a(n) (i)_____ effect on scholarship, othe
rs argue that the effects will be far more (ii)_____, claiming that academics ar
e sensible enough not to (iii)_____ unattributed sources.", "results" : [  [  "1
" ],  [  "1" ],  [  "0" ] ] }
>

指定返回title和results属性

默认会返回_id，也可以设置不返回

> db.choice.find({"_id":"005a38d5"},{"title":1,"results":1,"_id":0})
{ "title" : "While some maintain that the recent proliferation of uncredited web
sources will have a(n) (i)_____ effect on scholarship, others argue that the ef
fects will be far more (ii)_____, claiming that academics are sensible enough no
t to (iii)_____ unattributed sources.", "results" : [  [  "1" ],  [  "1" ],  [
"0" ] ] }
>

3.条件查询

条件操作符

"$lt"===============>"<"

"$lte"==============>"<="

"$gt"===============>">"

"$gte"==============>">="

"$ne"==============>"!="

查询出blankCount大于等于1，小于等于2的一条记录

> db.choice.findOne({"blankCount":{$lte:2,$gte:1}},{"blankCount":1})
{ "_id" : "006526ff", "blankCount" : 2 }
>

4.$or或

> db.choice.findOne({$or:[{"blankCount":2},{"type":3}]})

查询出blankCount为2或者type为3的一条记录

5.$not

> db.choice.findOne({"type":{"$not":{$gt:3}}})

查询出type不大于3的一条记录

6.查询空null的记录

> db.questionSet.findOne({source:null})

设置字段为null后，字段为null或者不包含该字段的记录也会匹配。

如果不查询不存在的字段，则使用$exists:true

> db.questionSet.findOne({source:null,$exists:true})

7.查询时使用正则表达式

> db.choice.findOne({title:/^While/})

查询title以While开头的一条记录

8.数组查询

> db.questionSet.findOne({"questionIds":'6188e9fc'},{"questionIds":1})
{
        "_id" : "030eeeba",
        "questionIds" : [
                "6188e9fc",
                "a380e38c",
                "addff709",
                "b6bc4eff",
                "5095b99f",
                "c8352e48",
                "ecca3626",
                "c31125f7"
        ]
}

查询数组questionIds中包含6188e9fc的记录

如果查询多个元素在数组中用$all，其中不分顺序。

> db.questionSet.findOne({"questionIds":{$all:['6188e9fc','a380e38c']}},{"questi
onIds":1})
{
        "_id" : "030eeeba",
        "questionIds" : [
                "6188e9fc",
                "a380e38c",
                "addff709",
                "b6bc4eff",
                "5095b99f",
                "c8352e48",
                "ecca3626",
                "c31125f7"
        ]
}

精确匹配：

> db.questionSet.findOne({"questionIds":['6188e9fc','a380e38c']},{"questionIds":
1})
null

9.$slice操作符

取出数组中的前3条记录

> db.questionSet.findOne({},{"questionIds":{$slice:3}})
{
        "_id" : "030eeeba",
        "catQuestionSet" : 2,
        "orderNo" : 2,
        "source" : 1,
        "type" : 2,
        "level" : 3,
        "questionCount" : 10,
        "questionIds" : [
                "6188e9fc",
                "a380e38c",
                "addff709"
        ]
}

取出数组中的后3条记录

> db.questionSet.findOne({},{"questionIds":{$slice:-3}})
{
        "_id" : "030eeeba",
        "catQuestionSet" : 2,
        "orderNo" : 2,
        "source" : 1,
        "type" : 2,
        "level" : 3,
        "questionCount" : 10,
        "questionIds" : [
                "c8352e48",
                "ecca3626",
                "c31125f7"
        ]
}

10.内嵌文档查询

查询文档有两种方式，一种是完全匹查询，另一种是针对键值对查询。内嵌文档的完全匹配查询和数组的完全匹配查询一样，内嵌文档内键值对的数量，顺序都必须一致才会匹配。

完全匹配：

> db.choice.findOne({"explain":{"ccurlList":"3DC334A16B187EBF9C33DC5901307461","
textExplain":"Answers"}})

键值对匹配(常用)：

> db.choice.findOne({"explain.ccurlList":"3DC334A16B187EBF9C33DC5901307461","exp
lain.textExplain":"Answers"})

数组中单条文档进行匹配时，使用$elemMatch

> db.choice.findOne({"explain":{$elemMatch:{"ccurlList":"3DC334A16B187EBF9C33DC5
901307461","textExplain":"Answers"}}})

11.$where查询

查询出blankCount和type相等的一条记录

> db.choice.findOne({$where:"this.blankCount==this.type"})
{
        "_id" : "005a38d5",
        "blankCount" : 3,
        "explain" : {
                "ccurlList" : [ ]
        },
        "type" : 3,
        "questionSetId" : "affccc14"
}