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,例如:
Users = new Model(someModelRules);
newUser = new Users(userInfomation);
数据模型User
有一个名为find()
的函数。现在,我想让 find()
链接起来,例如:
Users.find(" name = 'John' ")
.orderedBy("age").desc()
.limit(0,10)
或者可能只是一个简单的查找
:
Users.find(" name = 'John' ")
要编写这个find
函数,我相信我必须首先构建SQL,并在此find
链的末尾执行SQL查询。
我不知道该怎么做,我能想到的就是添加一个函数,例如:doQuery()
,这样当调用doQuery()
函数时我就会知道是时候执行SQL查询了,例如:
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,但我不需要额外的 doQuery()
函数。 :(
那么,我应该如何设计呢?如果您能给我一些带有注释的示例代码,那就太好了。
谢谢! (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,而且我几乎无法理解 ORM2 中的代码,因为没有注释。 (我不会使用 orm2。)
===================================解决方案===============================
受到@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');
运行这段代码,你将得到结果:
[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
我相信一定有更好的方法来实现这一目标,但这是我目前能得到的最好方法。 有意见吗?
最佳答案
如果您安排 doQuery
逻辑异步运行(但尽快),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.
}
<小时/>
一种完全不同的方法是使用单一方法来构建 SQL,并在选项对象中传递 ORDER BY 和 LIMIT 参数。那么你的调用将如下所示:
user.find({
what : " name = 'John' ",
orderedBy : "age DESC",
limit : "0,10"
});
这比您想要做的更适合 SQL 查询。你所拥有的看起来像 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)。
关于javascript - 如何设计链式 Model.find() 函数?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/17837922/