update

所有的更新操作都要求至少两个参数，第一个指明要更新的文档，第二个定义被选中的文档应该如何更新

第四个参数指定是否执行多项更新,MongoDB的更新操作默认只应用于查询选择器匹配到的第一个文档

source code

function (query, obj, upsert, multi) {
    assert(query, "need a query");
    assert(obj, "need an object");
    var firstKey = null;
    for (var k in obj) {
        firstKey = k;
        break;
    }
    if (firstKey != null && firstKey[0] == "$") {
        this._validateObject(obj);
    } else {
        this._validateForStorage(obj);
    }
    if (typeof upsert === "object") {
        assert(multi === undefined, "Fourth argument must be empty when specifying upsert and multi with an object.");
        opts = upsert;
        multi = opts.multi;
        upsert = opts.upsert;
    }
    this._db._initExtraInfo();
    this._mongo.update(this._fullName, query, obj, upsert ? true : false, multi ? true : false);
    this._db._getExtraInfo("Updated");
}
	

example

db.users.update({"pwd":"111111"},{$set:{userName:"bychjzh"}})
	

$set

修改某个属性要使用$set

example

同上：
 db.users.update({"pwd":"111111"},{$set:{userName:"bychjzh"}})
	

$unset

删除某个属性使用$unset

example

db.users.update({"pwd":"111111"},{$unset:{userName:1}})
	

$push

$push可以向数组中添加一个元素

example

> db.users.insert({"userName":"chjzh","pwd":"111","hobbies":["music","listening"]})
> db.users.find()
{ "_id" : ObjectId("513dad1d5a5c6b621c993e74"), "userName" : "chjzh", "pwd" : "123" }
{ "_id" : ObjectId("51428d3c2540dc509d6d3572"), "pwd" : "111111" }
{ "_id" : ObjectId("5143df5d0d5983f976e05adf"), "userName" : "chjzh", "pwd" : "111", "hobbies" : [ "music", "listening" ] }
> db.users.update({"pwd":"111"},{$push:{"hobbies":"table tenis"}},false,true)
> db.users.find()
{ "_id" : ObjectId("513dad1d5a5c6b621c993e74"), "userName" : "chjzh", "pwd" : "123" }
{ "_id" : ObjectId("51428d3c2540dc509d6d3572"), "pwd" : "111111" }
{ "_id" : ObjectId("5143df5d0d5983f976e05adf"), "hobbies" : [ "music", "listening", "table tenis" ], "pwd" : "111", "userName" : "chjzh" }
	

$addToSet

$addToSet同样可以向数组中添加元素，与$push不同的是$addToSet会保证元素的唯一性，防止重复添加

example

> db.users.update({"pwd":"111"},{$addToSet:{"hobbies":"table tenis"}},false,true)
> db.users.update({"pwd":"111"},{$addToSet:{"hobbies":"basketball"}},false,true)
> db.users.find()
{ "_id" : ObjectId("513dad1d5a5c6b621c993e74"), "userName" : "chjzh", "pwd" : "123" }
{ "_id" : ObjectId("51428d3c2540dc509d6d3572"), "pwd" : "111111" }
{ "_id" : ObjectId("5143df5d0d5983f976e05adf"), "hobbies" : [ "music", "listening", "table tenis", "basketball" ], "pwd" : "111", "userName" : "chjzh" }