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MongoDB：查询记录( Select )

• 数据库

上篇 blog 学习了 MongoDB 的插入，接下来学习数据查询相关的内容。MongoDB 查询有好几种方法，具体为以下：

基础表

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> db.test_2.find();  
{ "_id" : ObjectId("50a0d46ceb825d827b0c3f9b"), "id" : 1, "name" : "francs" }  
{ "_id" : ObjectId("50a0d46ceb825d827b0c3f9c"), "id" : 2, "name" : "fpZhou" }  
{ "_id" : ObjectId("50a0d46ceb825d827b0c3f9d"), "id" : 3, "name" : "tutu" } --find 游标查询  
{ "_id" : ObjectId("50a0d46deb825d827b0c3f9e"), "id" : 4, "name" : "am", "address" : "zhoushan" }

1 使用 Find 游标查询

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var cursor=db.test_2.find();  
while(cursor.hasNext()) printjson(cursor.next());
{  
 "_id" : ObjectId("50a0d46ceb825d827b0c3f9b"),  
 "id" : 1,  
 "name" : "francs"  
}  
{  
 "_id" : ObjectId("50a0d46ceb825d827b0c3f9c"),  
 "id" : 2,  
 "name" : "fpZhou"  
}  
{ "_id" : ObjectId("50a0d46ceb825d827b0c3f9d"), "id" : 3, "name" : "tutu" }  
{  
 "_id" : ObjectId("50a0d46deb825d827b0c3f9e"),  
 "id" : 4,  
 "name" : "am",  
 "address" : "zhoushan"  
}

备注：通过 while 循环，使用 next() 方法依次读取所有 document，并用 printjson 方法显示结果。

2 使用 Find 的 forEach（）查询

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> db.test_2.find().forEach(printjson);  
{  
 "_id" : ObjectId("50a0d46ceb825d827b0c3f9b"),  
 "id" : 1,  
 "name" : "francs"  
}  
{  
 "_id" : ObjectId("50a0d46ceb825d827b0c3f9c"),  
 "id" : 2,  
 "name" : "fpZhou"  
}  
{ "_id" : ObjectId("50a0d46ceb825d827b0c3f9d"), "id" : 3, "name" : "tutu" }  
{  
 "_id" : ObjectId("50a0d46deb825d827b0c3f9e"),  
 "id" : 4,  
 "name" : "am",  
 "address" : "zhoushan"  
}

3 定制查询

MongoDB 的查询和关系型数据库的查询差异较大，但大多数据的关系型数据库的查询可以转换成MongoDB 的查询，以下为简单的几种情况。

3.1 select * From test_2;

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> db.test_2.find();  
{ "_id" : ObjectId("50a0d46ceb825d827b0c3f9b"), "id" : 1, "name" : "francs" }  
{ "_id" : ObjectId("50a0d46ceb825d827b0c3f9c"), "id" : 2, "name" : "fpZhou" }  
{ "_id" : ObjectId("50a0d46ceb825d827b0c3f9d"), "id" : 3, "name" : "tutu" }  
{ "_id" : ObjectId("50a0d46deb825d827b0c3f9e"), "id" : 4, "name" : "am", "address" : "zhoushan" }

3.2 select id,name from test_2;

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> db.test_2.find({},{id:1,name:1});  
{ "_id" : ObjectId("50a0d46ceb825d827b0c3f9b"), "id" : 1, "name" : "francs" }  
{ "_id" : ObjectId("50a0d46ceb825d827b0c3f9c"), "id" : 2, "name" : "fpZhou" }  
{ "_id" : ObjectId("50a0d46ceb825d827b0c3f9d"), "id" : 3, "name" : "tutu" }  
{ "_id" : ObjectId("50a0d46deb825d827b0c3f9e"), "id" : 4, "name" : "am" }

3.3 select id from test_2;

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> db.test_2.find({},{id:1});  
{ "_id" : ObjectId("50a0d46ceb825d827b0c3f9b"), "id" : 1 }  
{ "_id" : ObjectId("50a0d46ceb825d827b0c3f9c"), "id" : 2 }  
{ "_id" : ObjectId("50a0d46ceb825d827b0c3f9d"), "id" : 3 }  
{ "_id" : ObjectId("50a0d46deb825d827b0c3f9e"), "id" : 4 }

3.4 select * From test_2 where id=1;

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> db.test_2.find({id:1});  
{ "_id" : ObjectId("50a0d46ceb825d827b0c3f9b"), "id" : 1, "name" : "francs" }

3.5 select id,address from test_2 where id=4;

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> db.test_2.find({address:'zhoushan'},{id:1,name:1});  
{ "_id" : ObjectId("50a0d46deb825d827b0c3f9e"), "id" : 4, "name" : "am" }

3.6 select * from test_2 where id=1 and name=’francs’

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> db.test_2.find({id:1,name:'francs'});  
{ "_id" : ObjectId("50a0d46ceb825d827b0c3f9b"), "id" : 1, "name" : "francs" }

备注：先学习这么多，其它更复杂的查询以后再补充。

4 Limit 用法

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> db.things.find();db.things.find();  
{ "_id" : ObjectId("50a0d637eb825d827b0c3f9f"), "id" : 1, "name" : "aaa" }  
{ "_id" : ObjectId("50a0d637eb825d827b0c3fa0"), "id" : 2, "name" : "aaa" }  
{ "_id" : ObjectId("50a0d637eb825d827b0c3fa1"), "id" : 3, "name" : "aaa" }  
{ "_id" : ObjectId("50a0d637eb825d827b0c3fa2"), "id" : 4, "name" : "aaa" }  
{ "_id" : ObjectId("50a0d637eb825d827b0c3fa3"), "id" : 5, "name" : "aaa" }  
{ "_id" : ObjectId("50a0d637eb825d827b0c3fa4"), "id" : 6, "name" : "aaa" }  
{ "_id" : ObjectId("50a0d637eb825d827b0c3fa5"), "id" : 7, "name" : "aaa" }  
{ "_id" : ObjectId("50a0d637eb825d827b0c3fa6"), "id" : 8, "name" : "aaa" }  
{ "_id" : ObjectId("50a0d637eb825d827b0c3fa7"), "id" : 9, "name" : "aaa" }  
{ "_id" : ObjectId("50a0d637eb825d827b0c3fa8"), "id" : 10, "name" : "aaa" }  
{ "_id" : ObjectId("50a0d637eb825d827b0c3fa9"), "id" : 11, "name" : "aaa" }  
{ "_id" : ObjectId("50a0d637eb825d827b0c3faa"), "id" : 12, "name" : "aaa" }  
{ "_id" : ObjectId("50a0d637eb825d827b0c3fab"), "id" : 13, "name" : "aaa" }  
{ "_id" : ObjectId("50a0d637eb825d827b0c3fac"), "id" : 14, "name" : "aaa" }  
{ "_id" : ObjectId("50a0d637eb825d827b0c3fad"), "id" : 15, "name" : "aaa" }  
{ "_id" : ObjectId("50a0d637eb825d827b0c3fae"), "id" : 16, "name" : "aaa" }  
{ "_id" : ObjectId("50a0d637eb825d827b0c3faf"), "id" : 17, "name" : "aaa" }  
{ "_id" : ObjectId("50a0d637eb825d827b0c3fb0"), "id" : 18, "name" : "aaa" }  
{ "_id" : ObjectId("50a0d637eb825d827b0c3fb1"), "id" : 19, "name" : "aaa" }  
{ "_id" : ObjectId("50a0d637eb825d827b0c3fb2"), "id" : 20, "name" : "aaa" }  
Type "it" for more
> db.things.find().limit(1);  
{ "_id" : ObjectId("50a0d637eb825d827b0c3f9f"), "id" : 1, "name" : "aaa" }

5 Skip 用法

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> db.things.find().skip(10).limit(1);  
{ "_id" : ObjectId("50a0d637eb825d827b0c3fa9"), "id" : 11, "name" : "aaa" }

6 Sorting 用法

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db.things.find().sort({id:1});

7 附：db.collection.find

The find() method selects documents in a collection and returns a cursor to the selected documents.
The find() method takes the following parameters.

Parameters:
1 query (document) – Optional. Specifies the selection criteria using query operators. Omit
the query parameter or pass an empty document (e.g. {}) to return all documents in the collection.
2 projection (document) –
Optional. Controls the fields to return, or the projection. The projection argument will resemble the
following prototype:
{ field1: boolean, field2: boolean … }
The boolean can take the following include or exclude values:
1 or true to include. The find() method always includes the _id field even if the field is not explicitly
stated to return in the projection parameter.
0 or false to exclude.
The projection cannot contain both include and exclude specifications except for the exclusion of the _id field.

Returns:
A cursor to the documents that match the query criteria and contain the projection fields.

原创文章，作者：6024010，如若转载，请注明出处：https://blog.ytso.com/237908.html

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