学习Mongodb笔记（三）——文档更新中高效的修改器

在MongoDB中，经常会对于文档进行更新，最简单的更新是用一个新文档完全替换匹配的文档，但是通常我们会对于一小部分更新，所以我们就需要使用原子性的更新修改器，指定对于文档中末些字段进行更新，更新修改器是种特殊的建，用来指定复杂的更新操作，如修改，添加或者删除键，还可能是操作数组或者内嵌文档。

1. $set修改器

$set  修改器用来指定一个键值。如果这个键不存在，则创建他，他对更新模式或者用户定义键来说非常方便。

> db.users.findOne(){        "_id" : ObjectId("56fe7df8b322e3ff1dabf834"),        "name" : "joe",        "age" : 30,        "sex" : "male",        "location" : "Wisconsin",        "favorite book" : "war and pace"}> db.users.update({"name":"joe"},{"$set":{"favorite book":["cat's cardle","foundation trilogy","ender's game"]}})WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })> db.users.findOne(){        "_id" : ObjectId("56fe7df8b322e3ff1dabf834"),        "name" : "joe",        "age" : 30,        "sex" : "male",        "location" : "Wisconsin",        "favorite book" : [                "cat's cardle",                "foundation trilogy",                "ender's game"        ]}

$unset修改器

$unset修改用于将键删除

> db.users.findOne(){        "_id" : ObjectId("56fe7df8b322e3ff1dabf834"),        "name" : "joe",        "age" : 30,        "sex" : "male",        "location" : "Wisconsin",        "favorite book" : [                "cat's cardle",                "foundation trilogy",                "ender's game"        ]}> db.users.update({"name":"joe"},{"$unset":{"favorite book":1}})WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })> db.users.findOne(){        "_id" : ObjectId("56fe7df8b322e3ff1dabf834"),        "name" : "joe",        "age" : 30,        "sex" : "male",        "location" : "Wisconsin"}

$inc修改器

$inc其用来增加或减少已有的键的键值，或者在键不存在的时候创建一个键。

> db.games.insert({"game":"pinball","user":"joe"})WriteResult({ "nInserted" : 1 })> db.games.findOne(){        "_id" : ObjectId("5770a1394f533aa7535d46d4"),        "game" : "pinball",        "user" : "joe"}> db.games.update({"game":"pinball","user":"joe"},{"$inc":{"score":50}})WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })> db.games.findOne(){        "_id" : ObjectId("5770a1394f533aa7535d46d4"),        "game" : "pinball",        "user" : "joe",        "score" : 50}

以上"$inc"与"$set"的用法类似，就是专门用来增加或减少数字的。"$inc"只能用于整数、长整数或双精度浮点数，要是在其他类型的数据上就会导致操作失败，其中包括很多语言会自动转换成数字的类型，例如null,布尔类型，或数字构成的字符串。"$inc"键的值必须为数字，不能使用字符串、数组和其他非数字的值，否则会报错，要修改其他类型，只能使用"$set"。

如下：

> db.foo.insert({"count":"1"})WriteResult({ "nInserted" : 1 })> db.foo.find(){ "_id" : ObjectId("5770befc4f533aa7535d46d5"), "count" : "1" }> db.foo.update({},{"$inc":{"count":1}})WriteResult({        "nMatched" : 0,        "nUpserted" : 0,        "nModified" : 0,        "writeError" : {                "code" : 16837,                "errmsg" : "Cannot apply $inc to a value of non-numeric type. {_id: ObjectId('5770befc4f533aa7535d46d5')} has the field 'count' of non-numeric type String"        }})> db.foo.update({},{$set:{count:2}})WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })> db.foo.find(){ "_id" : ObjectId("5770befc4f533aa7535d46d5"), "count" : 2 }>

数组修改器 $push

数组修改器，顾名思义它只可以用于操作数组，只能用在值为数组的键上。$push修改器如果指定的值已经存在，"$push"会想已有的数组末尾加入一个元素，要是没有就会创建一个新的数组。

> db.blog.findOne(){        "_id" : ObjectId("57709da84f533aa7535d46d3"),        "title" : "a blog post",        "author" : {                "name" : "joe schmoe op",                "email" : "[e-mail]"        }}> db.blog.update({"title":"a blog post"},{"$unset":{"author":1}})WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })> db.blog.findOne(){ "_id" : ObjectId("57709da84f533aa7535d46d3"), "title" : "a blog post" }> db.blog.update({"title":"a blog post"},{"$push":{"comments":{"name":"joe","email":"[e-mail]","content":"nice post"}}})WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })> db.blog.findOne(){        "_id" : ObjectId("57709da84f533aa7535d46d3"),        "title" : "a blog post",        "comments" : [                {                        "name" : "joe",                        "email" : "[e-mail]",                        "content" : "nice post"                }        ]}

数组修改器 $ne

$ne也是用来操作数组的修改器，在查询文档中，如果一个值不在数组里面就把他加进去，如果在不添加。

> db.users.insert({"name":"joe","emails":["[e-mail]","[e-mail]","[e-mail]"]})WriteResult({ "nInserted" : 1 })> db.users.findOne(){        "_id" : ObjectId("5770ca42e90c1adc80040a08"),        "name" : "joe",        "emails" : [                "[e-mail]",                "[e-mail]",                "[e-mail]"        ]}> db.users.update({"name":"joe","emails":{$ne:"[e-mail]"}},{$push:{"emails":"[e-mail]"}})WriteResult({ "nMatched" : 0, "nUpserted" : 0, "nModified" : 0 })                                    --nMatched为0表示没有修改> db.users.update({"name":"joe","emails":{$ne:"[e-mail]"}},{$push:{"emails":"[e-mail]"}})WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })> db.users.findOne(){        "_id" : ObjectId("5770ca42e90c1adc80040a08"),        "name" : "joe",        "emails" : [                "[e-mail]",                "[e-mail]",                "[e-mail]",                "[e-mail]"        ]}

以上这种方式也可以使用$addToSet实现。

 

 

数组修改器 $addToSet

$addToSet也是用来操作数组的修改器，实现的功能与$ne修改器相同，且更为方便。使用$addToSet修改器可以避免重复。

> db.users.findOne(){        "_id" : ObjectId("5770ca42e90c1adc80040a08"),        "name" : "joe",        "emails" : [                "[e-mail]",                "[e-mail]",                "[e-mail]",                "[e-mail]"        ]}> db.users.update({"_id":ObjectId("5770ca42e90c1adc80040a08")},{$addToSet:{"emails":"[e-mail]"}})WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 0 })     --原文档里已有"[e-mail]",修改完也没有产生重复值> db.users.findOne(){        "_id" : ObjectId("5770ca42e90c1adc80040a08"),        "name" : "joe",        "emails" : [                "[e-mail]",                "[e-mail]",                "[e-mail]",                "[e-mail]"        ]}> db.users.update({"_id":ObjectId("5770ca42e90c1adc80040a08")},{$addToSet:{"emails":"[e-mail]"}})WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })> db.users.findOne(){        "_id" : ObjectId("5770ca42e90c1adc80040a08"),        "name" : "joe",        "emails" : [                "[e-mail]",                "[e-mail]",                "[e-mail]",                "[e-mail]",                "[e-mail]"        ]}

 

 

 数组修改器 $each

$each数组修改器要和$addToSet修改结合起来用，可以一次添加多个不同的值。例如上面的例子中，我们一次添加多个email值， 如下：

> db.users.findOne(){        "_id" : ObjectId("5770ca42e90c1adc80040a08"),        "name" : "joe",        "emails" : [                "[e-mail]",                "[e-mail]",                "[e-mail]",                "[e-mail]",                "[e-mail]"        ]}> db.users.update({"_id":ObjectId("5770ca42e90c1adc80040a08")},{$addToSet:{$each:["[e-mail]","[e-mail]","[e-mail]"]}})WriteResult({        "nMatched" : 0,        "nUpserted" : 0,        "nModified" : 0,        "writeError" : {                "code" : 52,                "errmsg" : "The dollar ($) prefixed field '$each' in '$each' is not valid for storage."        }})> db.users.update({"_id":ObjectId("5770ca42e90c1adc80040a08")},{$addToSet:{"emails":{$each:["[e-mail]","[e-mail]","[e-mail]"]}}})WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })> db.users.findOne(){        "_id" : ObjectId("5770ca42e90c1adc80040a08"),        "name" : "joe",        "emails" : [                "[e-mail]",                "[e-mail]",                "[e-mail]",                "[e-mail]",                "[e-mail]",                "[e-mail]",                "[e-mail]"        ]}>

 数组修改器 $pop

$pop修改器主要于从数组中删除元素，他可以从数组中的任何一端删除元素，
例如:
{$pop:{key:1}} 从数组末尾删除一个元素
{$pop:{key:-1}} 从数组头部删除一个元素

> db.users.findOne(){        "_id" : ObjectId("5770ca42e90c1adc80040a08"),        "name" : "joe",        "emails" : [                "[e-mail]",                "[e-mail]",                "[e-mail]",                "[e-mail]",                "[e-mail]",                "[e-mail]",                "[e-mail]"        ]}> db.users.update({"name":"joe"},{$pop:{"emails":1}})WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })> db.users.findOne(){        "_id" : ObjectId("5770ca42e90c1adc80040a08"),        "name" : "joe",        "emails" : [                "[e-mail]",                "[e-mail]",                "[e-mail]",                "[e-mail]",                "[e-mail]",                "[e-mail]"        ]}> db.users.update({"name":"joe"},{$pop:{"emails":-1}})WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })> db.users.findOne(){        "_id" : ObjectId("5770ca42e90c1adc80040a08"),        "name" : "joe",        "emails" : [                "[e-mail]",                "[e-mail]",                "[e-mail]",                "[e-mail]",                "[e-mail]"        ]}

有时我们需要基于特定条件来删除元素，而不仅仅依据位置，就可以使用$pull修改器

 

 

 数组修改器 $pull

$pull修改器和$pop修改类似，都是用来删除数组中的元素
$pull可以基于特定条件来删除元素
$pull会将所有匹配到的数据全部删掉，如对数组[1,2,1,1]执行pull 1,得到的结果就是只有一个元素的数组[2]

例如我们想删除emails数组中的"[e-mail]"和"[e-mail]"两个元素：

> db.users.findOne(){        "_id" : ObjectId("5770ca42e90c1adc80040a08"),        "name" : "joe",        "emails" : [                "[e-mail]",                "[e-mail]",                "[e-mail]",                "[e-mail]",                "[e-mail]"        ]}> db.users.update({"name":"joe"},{$pull:{"emails":["[e-mail]","[e-mail]"]}})   WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 0 })  --好像不能一次删除多个，没有起作用> db.users.findOne(){        "_id" : ObjectId("5770ca42e90c1adc80040a08"),        "name" : "joe",        "emails" : [                "[e-mail]",                "[e-mail]",                "[e-mail]",                "[e-mail]",                "[e-mail]"        ]}> db.users.update({"name":"joe"},{$pull:{"emails":"[e-mail]"}})WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })> db.users.update({"name":"joe"},{$pull:{"emails":"[e-mail]"}})WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })> db.users.findOne(){        "_id" : ObjectId("5770ca42e90c1adc80040a08"),        "name" : "joe",        "emails" : [                "[e-mail]",                "[e-mail]",                "[e-mail]"        ]}

数组的定位修改器 $

若是数组有多个值，而我们只想对其中一部分进行操作，有两种方法可以实现这种操作。
两种方法操作数组中的值：通过位置或定位操作符("$")

数组都是以0开头的，可以将下标直接作为键来选择元素。

> db.blog.findOne(){        "_id" : ObjectId("57709da84f533aa7535d46d3"),        "title" : "a blog post",        "comments" : [                {                        "name" : "joe",                        "email" : "[e-mail]",                        "content" : "nice post"                },                {                        "name" : "bob",                        "email" : "[e-mail]",                        "content" : "good post"                }        ]}> db.blog.update({"title":"a blog post"},{$set:{"comments.1.name":"livan"}})WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })> db.blog.findOne(){        "_id" : ObjectId("57709da84f533aa7535d46d3"),        "title" : "a blog post",        "comments" : [                {                        "name" : "joe",                        "email" : "[e-mail]",                        "content" : "nice post"                },                {                        "name" : "livan",                        "email" : "[e-mail]",                        "content" : "good post"                }        ]}> db.blog.update({"title":"a blog post"},{$set:{"comments.1.email":"[e-mail]"}})WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })> db.blog.findOne(){        "_id" : ObjectId("57709da84f533aa7535d46d3"),        "title" : "a blog post",        "comments" : [                {                        "name" : "joe",                        "email" : "[e-mail]",                        "content" : "nice post"                },                {                        "name" : "livan",                        "email" : "[e-mail]",                        "content" : "good post"                }        ]}

在很多情况下，不预先查询文档就不能知道要修改数组的下标，为了克服这种困难，mongodb提供了定位操作符"$",
用来定位查询文档已经匹配的元素，并进行更新,定位符只更新第一个匹配的元素。
例如：用户john把名字改成了jim，就可以用定位符来替换评论中的名字:
db.blog.update({"comments.author":"john"},{$set:{"comments.$.author:"john"}})
可以理解为{"comments.author":"john"}查询条件定位到第一个元素，就执行{$set:{"comments.$.author:"john"}}，"$"定位符就表示找到的第一个元素

> db.blog.findOne(){        "_id" : ObjectId("57709da84f533aa7535d46d3"),        "title" : "a blog post",        "comments" : [                {                        "name" : "joe",                        "email" : "[e-mail]",                        "content" : "nice post"                },                {                        "name" : "livan",                        "email" : "[e-mail]",                        "content" : "good post"                }        ]}> db.blog.update({"comments.name":"livan"},{$set:{"comments.$.email":"[e-mail]"}})WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })> db.blog.update({"comments.name":"livan"},{$set:{"comments.$.name":"bob"}})WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })> db.blog.findOne(){        "_id" : ObjectId("57709da84f533aa7535d46d3"),        "title" : "a blog post",        "comments" : [                {                        "name" : "joe",                        "email" : "[e-mail]",                        "content" : "nice post"                },                {                        "name" : "bob",                        "email" : "[e-mail]",                        "content" : "good post"                }        ]}