一、批量更新
默认只对符合条件的一条文档更新
> db.post.find()
{ "_id" : ObjectId("54a530c3ff0df3732bac1681"), "id" : 2, "name" : "joe", "age" : 49 }
{ "_id" : ObjectId("54a530c3ff0df3732bac1680"), "id" : 1, "name" : "joe", "age" : 21, "comments" : [ "test2", "test9", "test5" ] }
> db.post.update({"name":"joe"}, {$set:{"age":70}})
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })
> db.post.find()
{ "_id" : ObjectId("54a530c3ff0df3732bac1681"), "id" : 2, "name" : "joe", "age" : 70 }
{ "_id" : ObjectId("54a530c3ff0df3732bac1680"), "id" : 1, "name" : "joe", "age" : 21, "comments" : [ "test2", "test9", "test5" ] } >
利用update的第四个参数进行批量更新：
> db.post.update({"name":"joe"}, {$set:{"age":30}},false,true)
WriteResult({ "nMatched" : 2, "nUpserted" : 0, "nModified" : 2 })> db.post.find()
{ "_id" : ObjectId("54a530c3ff0df3732bac1681"), "id" : 2, "name" : "joe", "age" : 30 }
{ "_id" : ObjectId("54a530c3ff0df3732bac1680"), "id" : 1, "name" : "joe", "age" : 30, "comments" : [ "test2", "test9", "test5" ] }
>附注：update方法参考
update( criteria, objNew, upsert, multi )
criteria : update的查询条件，类似sql update查询内where后面的
objNew : update的对象和一些更新的操作符（如$,$inc...）等，也可以理解为sql update查询内set后面的
upsert : 这个参数的意思是，无论false还是true，没有匹配的键则新增加一个；
multi : mongodb默认是false,只更新找到的第一条记录，如果这个参数为true,就把按条件查出来多条记录全部更新。
二、更新文档键值，无键值的则新增键值；
> db.post.update({"name":"joe"}, {$set:{"sex":1}},false,true)
WriteResult({ "nMatched" : 2, "nUpserted" : 0, "nModified" : 2 })
> db.post.find()
{ "_id" : ObjectId("54a530c3ff0df3732bac1681"), "id" : 2, "name" : "joe", "age" : 30, "sex" : 1 }
{ "_id" : ObjectId("54a530c3ff0df3732bac1680"), "id" : 1, "name" : "joe", "age" : 30, "comments" : [ "test2", "test9", "test5" ], "sex" : 1 }
> db.post.update({"name":"joe"}, {$set:{"school":"marry"}},true,true)
WriteResult({ "nMatched" : 2, "nUpserted" : 0, "nModified" : 2 })
> db.post.find()
{ "_id" : ObjectId("54a530c3ff0df3732bac1681"), "id" : 2, "name" : "joe", "age" : 30, "sex" : 1, "school" : "marry" }
{ "_id" : ObjectId("54a530c3ff0df3732bac1680"), "id" : 1, "name" : "joe", "age" : 30, "comments" : [ "test2", "test9", "test5" ], "sex" : 1, "school" : "marry" } >
