无法用聚合填充和构建文档

Question

所以我有这个模式，它有数据库中其他集合的外键。该文档有大约60k个帖子，每个帖子可以有多个类别，大约有200个类别。因此，我试图根据类别的外键获取和构建数据，并填充类别详细信息和计数。

主模式和类别模式如下:

const postSchema = new mongoose.Schema( {
post: {
type: mongoose.Schema.Types.ObjectId,
ref: 'PostDetails'
},
categories: [ {
category: {
type: mongoose.Schema.Types.ObjectId,
ref: 'Category'
},
subCategories: [ {
subCategory: {
type: mongoose.Schema.Types.ObjectId,
ref: 'Subcategory'
}
} ]
} ]
} );
const categorySchema = new mongoose.Schema( {
category: {
type: String,
},
categorySlug: {
type: String,
}
} );

我成功地进行了计数，但返回的数据不是我所期望的。返回的数据显示类别的id和计数，但没有名称和标识符。下面是它的样子:

[
{
"_id": [
"617acfd232c766589c23a90c"
],
"count": 876,
"category": []
}
]

我用下面的查询得到了上面的输出:

const aggregateStages = [ 
{
$group: {
_id: '$categories.category',
count: { $sum: 1 }
}
},
{
$lookup: {
from: "Category",
localField: "categories.category",
foreignField: "_id",
as: "category"
}
}
];
const categories = await Post.aggregate( aggregateStages ).exec();

我希望得到以下数据:

[
{
"_id": "617acfd232c766589c23a90c",
"count": 876,
"category": 'SomeCategory',
"categorySlug": 'some-category' 
}
]

我哪里出错了，我该如何解决它?

来自DB的示例数据

POST DATA
{
"_id": "617adad39054bae2c983c34f",
"post": "617ad1c80597c78ed4cc151e",
"author": "617acc689b309fdbbbdfdfe0",
"categories": [{
"category": "617acfd232c766589c23a8d1",
"subCategories":[]
}]
}
CATEGORY DATA
{
"_id": "617acfd232c766589c23a8d1",
"category": "Lorem Ipsum",
"categorySlug": "lorem-ipsum"
}

Answer 1

好的，看起来您可以通过使用$size运算符来解决这个问题。$size运算符将为您提供数组中元素的长度(或计数)。

现场演示

数据库

db={
"post": [
{
"_id": ObjectId("617adad39054bae2c983c34f"),
"post": ObjectId("617ad1c80597c78ed4cc151e"),
"author": ObjectId("617acc689b309fdbbbdfdfe0"),
"categories": [
{
"category": ObjectId("617acfd232c766589c23a8d1"),
"subCategories": []
}
]
}
],
"categories": [
{
"_id": ObjectId("617acfd232c766589c23a8d1"),
"category": "Lorem Ipsum",
"categorySlug": "lorem-ipsum"
}
]
}

查询

db.post.aggregate([
{
"$lookup": {
"from": "categories",
"localField": "categories.category",
"foreignField": "_id",
"as": "found_categories"
}
},
{
"$project": {
_id: "$_id",
count: {
"$size": "$found_categories"
},
"category": {
"$first": "$found_categories.category"
},
"categorySlug": {
"$first": "$found_categories.categorySlug"
}
}
}
])

结果

[
{
"_id": ObjectId("617adad39054bae2c983c34f"),
"category": "Lorem Ipsum",
"categorySlug": "lorem-ipsum",
"count": 1
}
]

虽然，我不相信这将给你你正在寻找的，如果找到一个以上的类别。如果它不工作，请让我知道，我会尽量帮助解决它。