javascript 如何在javascript中使用knex选择*？
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how to do select * from using knex in javascript?
提问by user1896766
I have a function like this:
我有一个这样的功能：
function get_projects() {
var project_names=[];
knex('projects').select('name').then(function (a) {
project_names.push(a);
})
return project_names;
}
This function executes the return statement return project_names;before completing project_names.push(a)statement and what I get after calling this function is an empty array, even though my db has results (I can see this if i log within the function a())
这个函数return project_names;在完成语句之前执行 return 语句project_names.push(a)，调用这个函数后我得到的是一个空数组，即使我的数据库有结果（如果我在函数 a() 中登录，我可以看到这个）
回答by Dewey
knex select() returns a promise so that you can continue the flow within then() function.
knex select() 返回一个 promise，以便您可以在 then() 函数中继续流程。
knex('projects').select('name').then(function(projectNames){
//do something here
console.log(projectNames);
});
回答by clay
Nodejs is asynchronous, so as soon as your line knex('projects').select('name').then...is executed, the line `return project_names;' is run. As you have found out, it didn't wait until it was filled with values!
Nodejs 是异步的，所以只要你的代码行knex('projects').select('name').then...被执行，`return project_names;' 行 正在运行。正如您所发现的，它并没有等到它充满了值！
The standard "return" at the end of the methods isn't a good programming style for Nodejs, which is event based. It has its place, but more common is a callback approach. Consider reading some tutorials on this new approach (I like this one)
方法末尾的标准“返回”不是基于事件的 Nodejs 的良好编程风格。它有它的位置，但更常见的是回调方法。考虑阅读一些关于这种新方法的教程（我喜欢这个）
You might change your current code to something like:
您可以将当前代码更改为以下内容：
function print_project_names() {
get_projects( function(names){
for( var i = 0; i < names.length; i++ )
{
console.log(names[i]+'\n');
}
});
}
function get_projects( callback ) {
var project_names=[];
knex('projects').select('name').then(function (a) {
project_names.push(a);
callback(project_names);
})
}
NOTE: This is not optimized code
注意：这不是优化代码
Here, when you want to print the project names (unsure your real goal), you are passing an actual function definition, as the "callback", into "get_projects". As the events fire, once the results are pushed into the project names, the callback is called with your new list.
在这里，当您想要打印项目名称（不确定您的真正目标）时，您将一个实际的函数定义作为“回调”传递到“get_projects”中。当事件触发时，一旦将结果推送到项目名称中，就会使用您的新列表调用回调。
回答by jemiloii
I know this is old, but you can do this:
我知道这是旧的，但你可以这样做：
function get_projects() {
return knex('projects').select('name')
.then(function (records) {
// already returns an array you can do other things here
return records;
})
}
Now you can do this to access the data.
现在您可以执行此操作来访问数据。
get_projects()
.then(function (records) {
// do what you need as well, like send to the frontend using express
res.send(records);
})
