mongoose 的 pupolate 联表查询

Question

const friendSchema = new mongoose.Schema({
    userID: String,    //用户id
    friend_list: Array,
    group_list: {
        A: [
            { "id": { type: mongoose.Schema.Types.ObjectId, ref: 'User' }, "nickName": String }
        ],
        B: [
            { "id": { type: mongoose.Schema.Types.ObjectId, ref: 'User' }, "nickName": String }
        ],
        C: [
            { "id": { type: mongoose.Schema.Types.ObjectId, ref: 'User' }, "nickName": String }
        ],
        D: [
            { "id": { type: mongoose.Schema.Types.ObjectId, ref: 'User' }, "nickName": String }
        ]
    }
})
module.exports = mongoose.model("friend", friendSchema);

这种数据结构 mongoose 怎么用 populate 联表查询填充id字段