我正在尝试从Post doc获取一个createdAt排序的评论列表,在该文档中,聚合管道将用于使用displayName和profilePhoto字段在评论字段中填充评论的所有者。
发布架构:
{
_owner: { type: Schema.Types.ObjectId, ref: 'User', required: true },
...
comments: [
{
_owner: { type: Schema.Types.ObjectId, ref: 'User' },
createdAt: Number,
body: { type: String, maxlength: 200 }
}
]
}
用户架构:
{
_id: '123abc'
profilePhoto: String,
displayName: String,
...
}
我要返回的内容:
[
{
"_id": "5bb5e99e040bf10b884b9653",
"_owner": {
"_id": "5bb51a97fb250722d4f5d5e1",
"profilePhoto": "https://...",
"displayName": "displayname"
},
"createdAt": 1538648478544,
"body": "Another comment"
},
{
"_id": "5bb5e96686f1973274c03880",
"_owner": {
"_id": "5bb51a97fb250722d4f5d5e1",
"profilePhoto": "https://...",
"displayName": "displayname"
},
"createdAt": 1538648422471,
"body": "A new comment"
}
]
我有一些工作代码,这些代码首先从聚合获取排序的注释,然后分别填充,但我希望能够仅通过使用聚合管道来获取此查询。
当前解决方案如下:
const postComments = await Post.aggregate([
{ $match: { _id: mongoose.Types.ObjectId(postId) } },
{ $unwind: '$comments' },
{ $limit: 50 },
{ $skip: 50 * page },
{ $sort: { 'comments.createdAt': -1 } },
{$replaceRoot: {newRoot: '$comments'}},
{
$project: {
_owner: 1,
createdAt: 1,
body: 1
}
}
]);
await Post.populate(postComments, {path: 'comments._owner', select: 'profilePhoto displayName' } )
答案 0 :(得分:1)
您可以尝试以下汇总
const postComments = await Post.aggregate([
{ "$match": { "_id": mongoose.Types.ObjectId(postId) } },
{ "$unwind": "$comments" },
{ "$lookup": {
"from": "users",
"localField": "comments._owner",
"foreignField": "_id",
"as": "comments._owner"
}},
{ "$unwind": "$comments._owner" },
{ "$replaceRoot": { "newRoot": "$comments" }},
{ "$sort": { "createdAt": -1 } }
{ "$limit": 50 }
])