猫鼬儿童

Question

我正在学习猫鼬，看着文档http://mongoosejs.com/docs/populate.html

然后我做了：

# initialize some TodoLists and their todos

l1 = new TodoList
    name: "List 1"
l2 = new TodoList
    name: "List 2"

t1 = new Todo 
    title: "Todo 1"
    desc: "Hello 1"
    list: l1._id
t2 = new Todo 
    title: "Todo 2"
    desc: "Hello 1"
    list: l1._id
t3 = new Todo 
    title: "Todo 3"
    dueOn: new Date 2012,6,1
    completedOn: new Date 2012,6,1
    list: l1._id
t4 = new Todo 
    title: "Todo 4"
    desc: "Hello 4"
    list: l2._id

# save all
async.parallel [
    (done) -> l1.save(done)
    (done) -> l2.save(done)
    (done) -> t1.save(done)
    (done) -> t2.save(done) 
    (done) -> t3.save(done)
    (done) -> t4.save(done)
], (err) -> 
    if !err
            # debugging
    Todo.find {}, (err, todos) ->
        console.log todos
            # the populate
    TodoList.findOne({ name: "List 2" })
            .populate("todos")
            .exec (err, list) ->
                console.log list
                done()
    else
        done err

我得到的是：

 [ { desc: 'Hello 1',
    list: 5026321c684d0a6b08000007,
    _id: 5026321c684d0a6b08000009,
    __v: 0 },
  { desc: 'Hello 1',
    list: 5026321c684d0a6b08000007,
    _id: 5026321c684d0a6b0800000a,
    __v: 0 },
  { dueOn: Sun Jul 01 2012 00:00:00 GMT+0800 (SGT),
    completedOn: Sun Jul 01 2012 00:00:00 GMT+0800 (SGT),
    list: 5026321c684d0a6b08000007,
    _id: 5026321c684d0a6b0800000b,
    __v: 0 },
  { desc: 'Hello 4',
    list: 5026321c684d0a6b08000008,
    _id: 5026321c684d0a6b0800000c,
    __v: 0 } ]
{ name: 'List 2',
  _id: 5026321c684d0a6b08000008,
  __v: 0,
  todos: [] }

Noice最后一行，todos没有填充，我希望它有Todo 4？

Answer 1

参考不是双向的。您已将引用保存到Todo'父级List，但您不会将Todo的引用存储到List.todos数组中。

假设您的列表架构类似于：

var ListSchema = new Schema({
  ...
  todos : [{ type: Schema.Types.ObjectId, ref: 'Todo' }]
});

然后你需要做一个list.todos.push(todo._id)。

Answer 2

通过使用以下代码，您无需在ListSchema中添加todos密钥。在定义ListSchema之后，只需输入以下代码：

ListSchema.virtual('todos', {
    ref: 'Post',
    localField: '_id',
    foreignField: 'list'
});

现在填写列表集合中的待办事项。

ListModel.find({}).populate('todos').exec((err, lists) => {
    if (err) return res.status(500).json(err);

    return res.status(200).json(lists);
});