尝试访问回送相关模型查询时JS对象的奇怪行为 [英] JS Object strange behaviour when trying access Loopback related model query

问题描述

我正在使用Loopback Framework，正在执行一个Web项目. 但是我认为我在这里提出的问题与此无关，而是与Javascript/Node.JS的一般知识有关.

I am working with the Loopback Framework, doing a web project. But I think that the question that I am exposing here has less to do with this, but with general Javascript / Node.JS knowledge.

在代码的一部分，我正在做

At one part of the code, I am doing:

roleMapping.find({
        where: {
            principalType: 'USER',
            principalId: context.principals[0].id
        },
        include: 'role'
    }, function(err, roles){
        console.log(roles[0]);
        for (var i in roles)
        {
            if (roles[i].role.name === 'teamLeader' &&
                roles[i].groupId === context.modelId)
            {
                cb(null,true);
            }else {
                cb(null,false);
            }
        }
});

可以，但是尝试比较roles[i].role.name时失败. 因此，我记录了roles[i]对象包含的内容.

Ok with this, but it fails when trying to compare roles[i].role.name. So, I went logging what the roles[i] object contained.

    { groupId: 1,
  id: 3,
  principalType: 'USER',
  principalId: 1,
  roleId: 2,
  role: 
   { id: 2,
     name: 'teamLeader',
     description: 'The leader(s) of a team',
     created: null,
     modified: null } }

好，没错，但是仍然失败，因此我尝试仅打印role属性.令我惊讶的是

Ok, nothing wrong, but it still fails, so I tried to print just the role property. And to my surprise:

{ [Function]
  update: [Function],
  destroy: [Function],
  create: [Function],
  build: [Function],
  _targetClass: 'Role' }

那么，role属性似乎是某种功能?但是以前如何正确打印呢?

So, the role property seems to be some sort of function? But how it was been correctly printed before?

最终，由于挫败感，我尝试了var role = JSON.parse(JSON.stringify(roles[i]));

Eventually, lost in my frustration I tried var role = JSON.parse(JSON.stringify(roles[i]));

然后我可以正常访问对象的每个属性，但这并不干净也不正常.

And then I could access every property of the object normally, but this is not clean nor normal.

这在JS编程年来是第一次让我大吃一惊(尽管有点业余)，如果有人可以向我澄清这一点，我将感到很高兴.谢谢

This blew my mind for the first time in years of JS programming (sort of amateurish though), and I would be pleased if someone could clarify this to me. Thanks

似乎它特定于此框架，所以我要更改标题以帮助社区.

It seems that it is specific to this Framework, so I'm changing title to help community.

推荐答案

我刚刚发现 issue 1425 链接到以下文档:

I just found issue 1425 which links to the following docs:

使用Node.js API，您需要调用toJSON()将包含相关项的返回模型实例转换为普通的JSON对象

With Node.js API, you need to call toJSON() to convert the returned model instance with related items into a plain JSON object

请注意，关联属性[…]指向关联方法的JavaScript 函数.

Please note the relation properties […] points to a JavaScript function for the relation method.

所以看来您必须使用

for (var i=0; i<roles.length; i++) {
    var x = roles[i].toJSON();
    cb(null, x.role.name === 'teamLeader'
             && x.groupId === context.modelId);
}

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