mongodb - $addFields where 条件

Question

我想在查找结果中添加额外的字段，但我需要一个条件。每个用户都有一个关系状态(本地字段)，应该将其添加到每个用户的查找结果中，但它会将每个“状态”添加到每个用户。

db.getCollection('relationships').aggregate([
    {$match: {
        user_id: ObjectId("5d3dbe07ea97db13d5b73195")}
    },
    {
       $lookup:
         {
           from: 'users',
           localField: 'relationship.user_id',
           foreignField: '_id',
           as: 'userss'
         }
    },
        {
        $addFields: {
            "userss.status": "$relationship.status"
        }
    },

])

用户模式

{
    "_id" : ObjectId("5d3dbe07ea97db13d5b73195"),
    "username" : "dipper",
    "email" : "test@test.com"
}

关系模式

{
    "user_id" : ObjectId("5d3dbe07ea97db13d5b73195"),
    "relationship" : [ 
        {
            "user_id" : ObjectId("5d3dbe17ea97db13d5b73196"),
            "status" : 0
        }, 
        {
            "user_id" : ObjectId("5d3dbe28ea97db13d5b73197"),
            "status" : 1
        }
    ]
}

我需要这样的结果:

{
    "_id" : ObjectId("5d3dbe07ea97db13d5b73196"),
    "username" : "mabel",
    "email" : "test@test.com",
    "status": 0

}
{
    "_id" : ObjectId("5d3dbe07ea97db13d5b73197"),
    "username" : "wendy",
    "email" : "test@test.com",
"status": 1

}

Answer 1

你需要$unwind为每个关系获取单个文档:

db.relationships.aggregate([
    {
        $match: { user_id: ObjectId("5d3dbe07ea97db13d5b73195") }
    },
    {
        $unwind: "$relationship"
    },
    {
        $lookup: {
            from: "users",
            localField: "relationship.user_id",
            foreignField: "_id",
            as: "user"
        }
    },
    {
        $unwind: "$user"
    },
    {
        $project: {
            _id:  "$relationship.user_id",
            username: "$user.username",
            email: "$user.email",
            status: "$relationship.status"
        }
    }
])