? ? 我们前面讲MongoDB的CRUD操作讲过：MongoDB的更新操作通过集合的update()函数实现。这个函数有两个参数：要更改的文档和更改后的样子。要更新文档有两种情况：更新文档和对文档某些部分更新。下面分别说说这两种情况：

??? 1.更新整个文档

??? 假设现在有下面的一个文档：

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{"name":"zhangsan","dad":"zhangyi","mom":"lisi"}; 

? ? 如果觉得这样不好，需要讲父亲和母亲的信息组织到一起，成为一个新的文档：parents，另外,加上一个年龄字段age.那么新的文档如下：

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{"name":"zhangsan","age":20,"parents":{dad:"zhangyi","mom":"lisi"}}; 

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??? 如果要将数据库中的第一个文档替代为上面第二个文档,使用update操作的过程如下:

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> var zhangsan = db.info.findOne({"name" : "zhangsan"}); 
> zhangsan 
{ 
    "_id" : ObjectId("4ee37409c3fc1a9f80ad74ed"), 
    "name" : "zhangsan", 
    "dad" : "zhangyi", 
    "mom" : "lisi" 
} 
> zhangsan.parents={"dad":zhangsan.dad,"mom":zhangsan.mom}; 
{ "dad" : "zhangyi", "mom" : "lisi" } 
> zhangsan 
{ 
    "_id" : ObjectId("4ee37409c3fc1a9f80ad74ed"), 
    "name" : "zhangsan", 
    "dad" : "zhangyi", 
    "mom" : "lisi", 
    "parents" : { 
        "dad" : "zhangyi", 
        "mom" : "lisi" 
    } 
} 
> zhangsan.age=20 
20 
> zhangsan 
{ 
    "_id" : ObjectId("4ee37409c3fc1a9f80ad74ed"), 
    "name" : "zhangsan", 
    "dad" : "zhangyi", 
    "mom" : "lisi", 
    "parents" : { 
        "dad" : "zhangyi", 
        "mom" : "lisi" 
    }, 
    "age" : 20 
} 
> delete zhangsan.dad 
true 
> zhangsan 
{ 
    "_id" : ObjectId("4ee37409c3fc1a9f80ad74ed"), 
    "name" : "zhangsan", 
    "mom" : "lisi", 
    "parents" : { 
        "dad" : "zhangyi", 
        "mom" : "lisi" 
    }, 
    "age" : 20 
} 
> delete zhangsan.mom 
true 
> zhangsan 
{ 
    "_id" : ObjectId("4ee37409c3fc1a9f80ad74ed"), 
    "name" : "zhangsan", 
    "parents" : { 
        "dad" : "zhangyi", 
        "mom" : "lisi" 
    }, 
    "age" : 20 
} 
> db.info.update({"_id" : ObjectId("4ee37409c3fc1a9f80ad74ed")},zhangsan); 
> db.info.find(); 
{ "_id" : ObjectId("4ee37409c3fc1a9f80ad74ed"), "name" : "zhangsan", "parents" : { "dad" : "zhangyi", "mom" : "lisi" }, "age" : 20 } 
>  

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? ? 以这种方式进行文档更新需要注意一点：尽量通过_id来匹配需要被替换的文档。至于为什么，我想用过数据库的人应该都能明白(类似于用主键去匹配特性的记录)。

??? 2.使用修改器部分修改文档的一部分

??? a) $set修改器

??? $set修改器指定一个键的新值，若不存在则创建新的。我们要给上面的zhangsan文档(数据库中的)添加一个wife键值对。

> db.info.update({"_id" : ObjectId("4ee37409c3fc1a9f80ad74ed")},{"$set":{"wife":"wangwu"}}); 
> db.info.find(); 
{ "_id" : ObjectId("4ee37409c3fc1a9f80ad74ed"), "age" : 20, "name" : "zhangsan", "parents" : { "dad" : "zhangyi", "mom" : "lisi" }, "wife" : "wangwu" } 
> 

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?? ? 现在过了一年，张三已经是21岁了，那么可以使用$set更新age键的值：

> db.info.update({"_id" : ObjectId("4ee37409c3fc1a9f80ad74ed")},{"$set":{"age":21}}); 
> db.info.find(); 
{ "_id" : ObjectId("4ee37409c3fc1a9f80ad74ed"), "age" : 21, "name" : "zhangsan", "parents" : { "dad" : "zhangyi", "mom" : "lisi" }, "wife" : "wangwu" } 
> 

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