Mongodb查询文档

系统管理员 2022-08-13 03:29 149阅读 0赞

Mongodb查询文档

> db.blog.find()     \--查看集合下的所有文档

\{ "\_id" :ObjectId("5438dd3fa7ccb1d4ecc7571d"), "title" : "myblog post", "conte

nt" : "here is blog past","date" : ISODate("2014-10-11T07:32:55.652Z")\}

\{ "\_id" :ObjectId("5438df80a7ccb1d4ecc7571e"), "name" : "blog","author" : "wan

gwei" \}

db.blog.find(\{\}).limit(50); 可以限制查询文档的数量

> db.blog.find(\{\}).limit(1);

\{ "\_id" :ObjectId("5438dd3fa7ccb1d4ecc7571d"), "title" : "myblog post", "conte

nt" : "here is blog past","date" : ISODate("2014-10-11T07:32:55.652Z")\}

> db.blog.find().pretty();  \---格式化查询文档加上pretty（）

"\_id" : ObjectId("5438dd3fa7ccb1d4ecc7571d"),

"title" : "my blog post",

"content" : "here is blog past",

"date" : ISODate("2014-10-11T07:32:55.652Z")

"\_id" : ObjectId("5438df80a7ccb1d4ecc7571e"),

"name" : "blog",

"author" : "wangwei"

> db.blog.findOne()  \----查看集合下一个文档

"\_id" : ObjectId("5438dd3fa7ccb1d4ecc7571d"),

"title" : "my blog post",

"content" : "here is blog past",

"date" : ISODate("2014-10-11T07:32:55.652Z")

> db.blog.find(\{ "name" :"blog" \}).limit(50).pretty()   \--按条件查询文档

"\_id" : ObjectId("5438df80a7ccb1d4ecc7571e"),

"name" : "blog",

"author" : "wangwei"

对于上面给出的例子相当于where子句 where name= ‘blog’

Mongodb中的and

> db.blog.find(\{ "name" :"blog", "author" : "wangwei" \}).limit(50);

\{ "\_id" :ObjectId("5438df80a7ccb1d4ecc7571e"), "name" :"blog", "author" : "wan

gwei" \}

> db.blog.find(\{ "name" :"blog", "author" : "wangweidd" \}).limit(50);

> --返回为空

对于上面给出的例子相当于where子句 where name= ‘blog’ and author =’wangwei’

Mongodb中的or

> db.blog.find(\{ "$or" : \[\{"name" : "blog" \}, \{ "title" : "my blogpost" \}\] \}).

limit(50).pretty()

"\_id" : ObjectId("5438dd3fa7ccb1d4ecc7571d"),

"title" : "my blog post",

"content" : "here is blog past",

"date" : ISODate("2014-10-11T07:32:55.652Z")

"\_id" : ObjectId("5438df80a7ccb1d4ecc7571e"),

"name" : "blog",

"author" : "wangwei"

对于上面给出的例子相当于where子句 where name= ‘blog’ or title =’ myblog post’

> db.blog.find(\{ "name" :"blog" \}, \{ "name" : 1 \}).limit(50).pretty();   \--查询显示特定列（字段）

\{ "\_id" :ObjectId("5438df80a7ccb1d4ecc7571e"), "name" :"blog" \}

对于上面给出的例子相当于 select name from

> db.blog.find(\{ "name" :"blog" \}, \{ "name" : 1 \}).limit(50).sort(\{ "name": -

\});    --按字段排序查询

\{ "\_id" :ObjectId("5438df80a7ccb1d4ecc7571e"), "name" :"blog" \}

sort() 方法接受一个文档，其中包含的字段列表连同他们的排序顺序。要指定排序顺序1和\-1。 1用于升序排列，而\-1用于降序。

**RDBMS Where子句和MongoDB等同语句**

要查询文件的一些条件的基础上，可以使用下面的操作 www.yiibai.com

<table style="background:#F7F7F7"> 
 <tbody> 
 <tr> 
 <td style="background:#EEEEEE"> 操作 </td> 
 <td style="background:#EEEEEE"> 语法 </td> 
 <td style="background:#EEEEEE"> 例子 </td> 
 <td style="background:#EEEEEE"> RDBMS 等同 </td> 
 </tr> 
 <tr> 
 <td> Equality </td> 
 <td> {&lt;key&gt;:&lt;value&gt;} </td> 
 <td> db.mycol.find({"by":"tutorials point"}).pretty() </td> 
 <td> where by = 'tutorials point' </td> 
 </tr> 
 <tr> 
 <td> Less Than </td> 
 <td> {&lt;key&gt;:{$lt:&lt;value&gt;}} </td> 
 <td> db.mycol.find({"likes":{$lt:50}}).pretty() </td> 
 <td> where likes &lt; 50 </td> 
 </tr> 
 <tr> 
 <td> Less Than Equals </td> 
 <td> {&lt;key&gt;:{$lte:&lt;value&gt;}} </td> 
 <td> db.mycol.find({"likes":{$lte:50}}).pretty() </td> 
 <td> where likes &lt;= 50 </td> 
 </tr> 
 <tr> 
 <td> Greater Than </td> 
 <td> {&lt;key&gt;:{$gt:&lt;value&gt;}} </td> 
 <td> db.mycol.find({"likes":{$gt:50}}).pretty() </td> 
 <td> where likes &gt; 50 </td> 
 </tr> 
 <tr> 
 <td> Greater Than Equals </td> 
 <td> {&lt;key&gt;:{$gte:&lt;value&gt;}} </td> 
 <td> db.mycol.find({"likes":{$gte:50}}).pretty() </td> 
 <td> where likes &gt;= 50 </td> 
 </tr> 
 <tr> 
 <td> Not Equals </td> 
 <td> {&lt;key&gt;:{$ne:&lt;value&gt;}} </td> 
 <td> db.mycol.find({"likes":{$ne:50}}).pretty() </td> 
 <td> where likes != 50 </td> 
 </tr> 
 </tbody> 
</table>