我正在尝试在Node.js中编写ORM。我想声明一个名为Model的类,它将用于声明一个数据对象,如:
Users = new Model(someModelRules);
newUser = new Users(userInfomation);
数据模型User
有一个名为find()
的函数。现在,我想将find()
链接起来,例如:
Users.find(" name = 'John' ")
.orderedBy("age").desc()
.limit(0,10)
或者只是一个简单的find
:
Users.find(" name = 'John' ")
编写此find
函数的代码,我相信我必须首先构建SQL,并在此find
链的末尾执行SQL查询。
我不知道怎么做,我能想到的是添加一个像doQuery()
这样的函数,所以我知道是时候在doQuery()
函数时进行SQL查询了被称为,如:
Users.find(" name = 'John' ")
.orderedBy("age").desc()
.limit(0,10)
.doQuery();
我知道这是一个简单的解决方案,但我不想要额外的doQuery()
功能。 :(
那么,我该如何设计呢?如果您能向我展示一些带注释的示例代码,那将是非常好的。
THX! (抱歉我的英语不好)
PS。我知道ORM2有一个我想要的查找功能,但我想知道如何编码它,我几乎无法理解ORM2中的代码,因为没有注释。 (我不会用orm2。)
=================================解决方案============= =================
受@bfavaretto的启发:
function User() {
this.find = function(id, condition) {
return new findChain(id, condition);
}
}
function findChain(id, condition) {
this._id = id
this._condition = condition
this.queryTimerSet = false;
this.scheduleQuery = function () {
var self = this;
if(!self.queryTimerSet) {
console.log('[TEST CASE: ' + self._id + '] Insert query into eventLoop');
setTimeout(function(){
console.log('[TEST CASE: ' + self._id + '] Start query: '+self._condition);
}, 0);
self.queryTimerSet = true;
} else {
console.log('[TEST CASE: ' + self._id + '] No need to insert another query');
}
}
this.orderedBy = function(column) {
console.log('[TEST CASE: ' + this._id + '] orderedBy was called');
this._condition = this._condition + ' ORDER BY ' + column
this.scheduleQuery();
return this;
}
this.desc = function() {
// simply add DESC to the end of sql
this._condition = this._condition + ' DESC'
}
this.scheduleQuery();
}
var user = new User();
user.find(1,'SELECT * FROM test').orderedBy('NAME1').desc();
user.find(2,'SELECT * FROM test').orderedBy('NAME2');
user.find(3,'SELECT * FROM test');
运行此代码,您将得到结果:
[TEST CASE: 1] Insert query into eventLoop
[TEST CASE: 1] orderedBy was called
[TEST CASE: 1] No need to insert another query
[TEST CASE: 2] Insert query into eventLoop
[TEST CASE: 2] orderedBy was called
[TEST CASE: 2] No need to insert another query
[TEST CASE: 3] Insert query into eventLoop
[TEST CASE: 1] Start query: SELECT * FROM test ORDER BY NAME1 DESC
[TEST CASE: 2] Start query: SELECT * FROM test ORDER BY NAME2
[TEST CASE: 3] Start query: SELECT * FROM test
我相信必须有更好的方法来实现这一目标,但这是我现在能做的最好的方法。 有什么意见吗?
答案 0 :(得分:1)
如果您安排doQuery
逻辑以异步方式运行(但是尽快),则可以实现这一点。我正在考虑这样的事情:
function User() {
// Flag to control whether a timer was already setup
var queryTimerSet = false;
// This will schedule the query execution to the next tick of the
// event loop, if it wasn't already scheduled.
// This function is available to your model methods via closure.
function scheduleQuery() {
if(!queryTimerSet) {
setTimeout(function(){
// execute sql
// from the query callback, set queryTimerSet back to false
}, 0);
queryTimerSet = true;
}
}
this.find = function() {
// ... logic that builds the sql
scheduleQuery();
return this;
}
this.orderedBy = function() {
// ... logic that appends to the sql
scheduleQuery();
return this;
}
// etc.
}
一种完全不同的方法是使用单个方法构建SQL,并在选项对象中传递ORDER BY和LIMIT参数。然后你的电话会是这样的:
user.find({
what : " name = 'John' ",
orderedBy : "age DESC",
limit : "0,10"
});
这比您尝试的更适合SQL查询。你有什么看起来像MongoDB之类的noSQL东西,其中获取记录和排序是单独的操作(我认为)。
答案 1 :(得分:0)
您将始终必须在链的末尾有一个execute / doQuery函数。 这是因为doQuery之前的所有其他函数都有助于构建最终需要执行的查询。