MongoDB使用BSON文件存储在collection中，本文主要介绍MongoDB中的写操作和优化策略。
主要有三种写操作：
Create
Update
Delete
Create：可以分为两种基本操作——insert和updates with the upsert option
Insert（）
BSON文件最大为16M；_id通常作为主key
为了测试写操作是否成功，可以调用getLastError函数{ getLastError: 1 }
db.collection.insert( <document> )
insert方法在第一次调用的时候，自动创建collection。
以下例子中bios为collection名，根据自己情况修改。
例如:
db.bios.insert(
{
_id: 1,
name: { first: 'John', last: 'Backus' },
birth: new Date('Dec 03, 1924'),
death: new Date('Mar 17, 2007'),
contribs: [ 'Fortran', 'ALGOL', 'Backus-Naur Form', 'FP' ],
awards: [
{
award: 'W.W. McDowell Award',
year: 1967,
by: 'IEEE Computer Society'
},
{
award: 'National Medal of Science',
year: 1975,
by: 'National Science Foundation'
},
{
award: 'Turing Award',
year: 1977,
by: 'ACM'
},
{
award: 'Draper Prize',
year: 1993,
by: 'National Academy of Engineering'
}
]
}
)
如果插入操作没有指定_id，则会自动生成一个唯一的id。
使用中括号，同时插入多个文档。
db.bios.insert(
[
{
_id: 3,
name: { first: 'Grace', last: 'Hopper' },
title: 'Rear Admiral',
birth: new Date('Dec 09, 1906'),
death: new Date('Jan 01, 1992'),
contribs: [ 'UNIVAC', 'compiler', 'FLOW-MATIC', 'COBOL' ],
awards: [
{
award: 'Computer Sciences Man of the Year',
year: 1969,
by: 'Data Processing Management Association'
},
{
award: 'Distinguished Fellow',
year: 1973,
by: ' British Computer Society'
},
{
award: 'W. W. McDowell Award',
year: 1976,
by: 'IEEE Computer Society'
},
{
award: 'National Medal of Technology',
year: 1991,
by: 'United States'
}
]
},
{
_id: 4,
name: { first: 'Kristen', last: 'Nygaard' },
birth: new Date('Aug 27, 1926'),
death: new Date('Aug 10, 2002'),
contribs: [ 'OOP', 'Simula' ],
awards: [
{
award: 'Rosing Prize',
year: 1999,
by: 'Norwegian Data Association'
},
{
award: 'Turing Award',
year: 2001,
by: 'ACM'
},
{
award: 'IEEE John von Neumann Medal',
year: 2001,
by: 'IEEE'
}
]
},
{
_id: 5,
name: { first: 'Ole-Johan', last: 'Dahl' },
birth: new Date('Oct 12, 1931'),
death: new Date('Jun 29, 2002'),
contribs: [ 'OOP', 'Simula' ],
awards: [
{
award: 'Rosing Prize',
year: 1999,
by: 'Norwegian Data Association'
},
{
award: 'Turing Award',
year: 2001,
by: 'ACM'
},
{
award: 'IEEE John von Neumann Medal',
year: 2001,
by: 'IEEE'
}
]
}
]
)
调用save（）函数，通过查询collection中的_id域，来决定使用insert还是update。
upsert flags 当插入的文档已经存在，需要对原文当进行覆盖的时候使用此标记。
db.collection.update( <query>,
<update>,
{ upsert: true } )
如果没有文档符合查询要求<query>，则插入文档，举例如下：
db.bios.update(
{
_id: 7,
name: { first: 'Ken', last: 'Thompson' }
},
{
$set: {
birth: new Date('Feb 04, 1943'),
contribs: [ 'UNIX', 'C', 'B', 'UTF-8' ],
awards: [
{
award: 'Turing Award',
year: 1983,
by: 'ACM'
},
{
award: 'IEEE Richard W. Hamming Medal',
year: 1990,
by: 'IEEE'
},
{
award: 'National Medal of Technology',
year: 1998,
by: 'United States'
},
{
award: 'Tsutomu Kanai Award',
year: 1999,
by: 'IEEE'
},
{
award: 'Japan Prize',
year: 2011,
by: 'The Japan Prize Foundation'
}
]
}
},
{ upsert: true } //如果文档存在，覆盖
)
Update（）
主要包括两种操作，update和save
db.collection.update( <query>, <update>, <options>
使用方法同insert中介绍。
下面分情况举例：
1、更新文件中的域
db.bios.update(
{ _id: 1 },
{
$set: { 'name.middle': 'Warner' },
}
)
更新子文档name中的middle域为warner
2、添加新的域
db.bios.update(
{ _id: 3 },
{ $set: {
mbranch: 'Navy',
'name.aka': 'Amazing Grace'
}
}
)
添加mbranch域 和子文档name的aka域
3、移除域
db.bios.update(
{ _id: 3 },
{ $unset: { birth: 1 } }
)
4、更新数组
db.bios.update(
{ _id: 1 },
{ $set: { 'contribs.1': 'ALGOL 58' } }
)
更新contribs数组中第二个元素的值
5、定位，然后更新元素
db.bios.update(
{ _id: 3, 'contribs': 'compiler' },
{ $set: { 'contribs.$': 'A compiler' } }
)
定位id为3，contribs中存在compiler元素的位置，更新为A compiler
6、向数组添加元素
db.bios.update(
{ _id: 1 },
{
$push: { awards: { award: 'IBM Fellow', year: 1963, by: 'IBM' } }
}
)
添加一个新的awards域的元素
7、更新多个文档
db.bios.update(
{ 'awards.award': 'Turing' },
{ $set: { turing: true } },
{ multi: true }
)
save（）函数可以用以下函数来解释：function save( doc ) {
if( doc["_id"] ) {
update( {_id: doc["_id"] }, doc, { upsert: true } );
}
else {
insert(doc);
}
}
Update Operators 操作符
Fields
| Name | Description |
|---|
| $inc |
Increments the value of the field by the specified amount. |
| $rename |
Renames a field. |
| $setOnInsert |
Sets the value of a field upon documentation creation during an upsert. Has no effect on update operations that modify existing documents. |
| $set |
Sets the value of a field in an existing document. |
| $unset |
Removes the specified field from an existing document. |
Array Operators
| Name | Description |
|---|
| $ |
Acts as a placeholder to update the first element that matches the query condition in an update. |
| $addToSet |
Adds elements to an existing array only if they do not already exist in the set. |
| $pop |
Removes the first or last item of an array. |
| $pullAll |
Removes multiple values from an array. |
| $pull |
Removes items from an array that match a query statement. |
| $pushAll |
Deprecated. Adds several items to an array. |
| $push |
Adds an item to an array. |
Modifiers
| Name | Description |
|---|
| $each |
Modifies the $push and $addToSet operators to append multiple items for array updates. |
| $slice |
Modifies the $push operator to limit the size of updated arrays. |
| $sort |
Modifies the $push operator to reorder documents stored in an array. |
Bitwise
| Name | Description |
|---|
| $bit |
Performs bitwise AND and OR updates of integer values. |
Isolation
| Name | Description |
|---|
| $isolated |
Modifies behavior of multi-updates to improve the isolation of the operation. |