MongoDB入门3——更新文档和修改器1

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：
 
 
 
 
{"name":"zhangsan","dad":"zhangyi","mom":"lisi"};  
 
{"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：
 
 
 
 
{"name":"zhangsan","age":20,"parents":{dad:"zhangyi","mom":"lisi"}};  
 
{"name":"zhangsan","age":20,"parents":{dad:"zhangyi","mom":"lisi"}}; 
 
    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:
 
 
 
 
> 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 }   
>   
 
> 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 }
>  
 
    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" }   
>  
 
> 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" }
> 
 
     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" }   
>  
 
> 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" }
> 
 
     当然这种情况还有别的修改器可以实现，并且更合适，我们一会会继续介。
 
     zhangsan离婚了，没老婆了，怎们办？我们可以通过$unset修改器来撤销wife这个键值对。（PS：这个例子不是很合适，太残酷了）
 
 
 
 
> db.info.update({"_id" : ObjectId("4ee37409c3fc1a9f80ad74ed")},{"$unset":{"wife":1}});   
> db.info.find();   
{ "_id" : ObjectId("4ee37409c3fc1a9f80ad74ed"), "age" : 21, "name" : "zhangsan", "parents" : { "dad" : "zhangyi", "mom" : "lisi" } }   
>  
 
> db.info.update({"_id" : ObjectId("4ee37409c3fc1a9f80ad74ed")},{"$unset":{"wife":1}});
> db.info.find();
{ "_id" : ObjectId("4ee37409c3fc1a9f80ad74ed"), "age" : 21, "name" : "zhangsan", "parents" : { "dad" : "zhangyi", "mom" : "lisi" } }
> 
 
 
 
    b)$inc修改器
 
    $inc修改器增加和修改已有键的值（只适用于数字类型）。上面我们提到，随着时间推移，zhangsan的年龄会不断增大，就可以使用这个修改器：
 
 
 
 
> db.info.update({"_id" : ObjectId("4ee37409c3fc1a9f80ad74ed")},{"$inc":{"age":1}});   
> db.info.find();   
{ "_id" : ObjectId("4ee37409c3fc1a9f80ad74ed"), "age" : 22, "name" : "zhangsan", "parents" : { "dad" : "zhangyi", "mom" : "lisi" } }   
>   
 
> db.info.update({"_id" : ObjectId("4ee37409c3fc1a9f80ad74ed")},{"$inc":{"age":1}});
> db.info.find();
{ "_id" : ObjectId("4ee37409c3fc1a9f80ad74ed"), "age" : 22, "name" : "zhangsan", "parents" : { "dad" : "zhangyi", "mom" : "lisi" } }
>  
 
 
 
    这个修改器非常适合那些投票、计分、访问量统计一类的情况。但是得注意，这个选择器只适用于对数字类型的键值对进行增加和减少。减少只需要传递负值就可以了


摘自 wawlian说