您想要冰箱和所有子类别？
而且异步也是个问题？
我认为你可以在这里使用聚合。
假设您正在寻找一个带有 _id 变量的类别，该变量是您想要的 ObjectId，它是子类别。
db.yourCollection.aggregate({
// get stuff where you have the parent or subcats.
$match: {
$or: [
{_id: ObjectId("54de8b9f022ff38bbf5e0530")},
{parent: ObjectId("54de8b9f022ff38bbf5e0530")}
]
}
},
// reshape the data you'll need further on from each mached doc
{
$project: {
_id: false,
data: {
id: '$_id',
name: '$name'
// I guess you'll also want the `slug` and `image` here.
// but that's homework :)
},
parent: '$parent'
}
},
// now put a common _id so you can group them, and also put stuff into arrays
{
$project: {
id: {$literal: 'id'},
mainCategory: {
// if our parent is null, put our data.
// otherwise put null here.
$cond: [{$eq: [null, '$parent']}, {_id: '$data.id', name: '$data.name'}, undefined]
},
subcat: {
// here is the other way around.
$cond: [{$ne: [null, '$parent']}, {_id: '$data.id', name: '$data.name'}, null]
}
}
// that stage produces for each doc either a mainCat or subcat
// (and the other prop equals to null)
},
// finally, group the things so you can have them together
{
$group: {
_id: '$id',
// a bit hacky, but mongo will yield to it
mainCategory: {$max: '$mainCategory'},
subCategories: {
// this will, unfortunately, also add the `null` we have
// assigned to main category up there
$addToSet: '$subcat'
}
}
},
// so we get rid of the unwanted _id = 'id' and the null from subcats.
{
$project: {
_id: false,
mainCategory: 1,
subCategories: {
$setDifference: ['$subCategories', [null]]
}
}
})
给定这个数据集：
[{
"_id" : ObjectId("54de8b9f022ff38bbf5e0530"),
"name" : "Fridge",
"parent" : null
},
{
"_id" : ObjectId("54de8bba022ff38bbf5e0531"),
"name" : "choco",
"parent" : ObjectId("54de8b9f022ff38bbf5e0530")
},
{
"_id" : ObjectId("54de8bc8022ff38bbf5e0532"),
"name" : "apple",
"parent" : ObjectId("54de8b9f022ff38bbf5e0530")
}
我得到这个结果：
{
"result" : [
{
"mainCategory" : {
"_id" : ObjectId("54de8b9f022ff38bbf5e0530"),
"name" : "Fridge"
},
"subCategories" : [
{
"_id" : ObjectId("54de8bc8022ff38bbf5e0532"),
"name" : "apple"
},
{
"_id" : ObjectId("54de8bba022ff38bbf5e0531"),
"name" : "choco"
}
]
}
],
"ok" : 1
}
对于异步，通常你会这样做：
db.collection.aggregate(thePipeLineAbove, function(err, results) {
// handle err
if (err) {
// deal with it
} else {
console.log(results);
}
});
但这在一定程度上取决于您的 MongoDB 驱动程序。
即使你有更深的层次结构，你也可以扩展它。