MongoDB的基本操作

MongoDB的基本操作有：添加 删除 更新 和 读取

启动MongoDB Shell：命令行输入mongo（Centos 7）

[root@jans test]# mongo
MongoDB shell version: 2.6.12
connecting to: test
Server has startup warnings: 
2017-08-31T17:54:18.621+0800 [initandlisten] 
2017-08-31T17:54:18.621+0800 [initandlisten] ** WARNING: Readahead for /var/lib/mongodb is set to 4096KB
2017-08-31T17:54:18.621+0800 [initandlisten] **          We suggest setting it to 256KB (512 sectors) or less
2017-08-31T17:54:18.621+0800 [initandlisten] **          http://dochub.mongodb.org/core/readahead
> 

添加文档：

> db.test.insert({"key_a":"value_a"})
WriteResult({ "nInserted" : 1 })
> db.test.insert({"key_b":"value_b"})
WriteResult({ "nInserted" : 1 })

读取文档：

find()可查询多个符合条件的文档，findOne()只查询一个，

> db.test.find()
{ "_id" : ObjectId("5a12da411c97109757a27d5d"), "key_a" : "value_a" }
{ "_id" : ObjectId("5a12dab51c97109757a27d5e"), "key_b" : "value_b" }

> db.test.findOne()
{ "_id" : ObjectId("5a12da411c97109757a27d5d"), "key_a" : "value_a" }

> db.test.findOne({"key_b" : "value_b"})
{ "_id" : ObjectId("5a12dab51c97109757a27d5e"), "key_b" : "value_b" }
> db.test.findOne({"_id" : ObjectId("5a12da411c97109757a27d5d")})
{ "_id" : ObjectId("5a12da411c97109757a27d5d"), "key_a" : "value_a" }

更新文档：

> db.test.insert({"key_c":"value_c"})
WriteResult({ "nInserted" : 1 })

> db.test.findOne({"key_c" : "value_c"})
{ "_id" : ObjectId("5a12e0a38710e2c2442eda15"), "key_c" : "value_c" }
> db.test.update(db.test.findOne({"key_c":"value_c"}),  {"new_key_c" : "new_value_c","key_c" : "value_c"})
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })

> db.test.findOne({"key_c":"value_c"})
{
    "_id" : ObjectId("5a12e0a38710e2c2442eda15"),
    "new_key_c" : "new_value_c",
    "key_c" : "value_c"
}

删除文档：

> db.test.remove({"key_c":"value_c"})
WriteResult({ "nRemoved" : 1 })
> db.test.findOne({"key_c":"value_c"})
null