如何根据另一个属性选择一个属性-mongodb [英] how to select a property depending another property - mongodb

问题描述

我正在使用mongoose.我想根据此处type上的另一个属性来选择users属性.

I'm using mongoose. I want to select users property depending on another property at this here type.

例如，当我的type是private时，我要选择users.

for example when my type is private I want to select users.

Conversation.find({
users: {
$elemMatch: {
user: _id
  }
 }
},{
 title: 1,
 type: 1,
 users:1 // when `type` is `private` I want to this field to be one.
});

我的模式:

const ConversationSchema = new Schema({
    type: {type: String, enum: ['private', 'group'], default: 'private'},
    creator: {type: Schema.Types.ObjectId, ref: 'User', index: true, required: true}, // creator
    // for group,
    title: String, 
    picture: String,
    description: String,
    users: [
        {
            user: { type: Schema.Types.ObjectId, index: true, reuqired:  true, unique: true }, 
            role: { type: String, enum: ['admin', 'member'], default: 'member' },
            mute: { type:  Boolean, default: false },
            type: {type: String, enum: ['private', 'group'], default: 'private'},
        }
    ],
}, { timestamps: true });

推荐答案

您可以通过使用" rel ="nofollow noreferrer">删除.您的情况应该是:

You can conditionally exclude fields by using REMOVE in aggregation. In your case, it should be:

Conversation.aggregate([
  {$match: {"users.user": id}},
  {
     $project: {
       title: 1,
       type: 1,
       users: {
         $cond: { 
           if: { $eq: [ "$type", "private" ] }, 
           then: "$users", 
           else: "$$REMOVE" 
         }
       }
     }
  }
])

旁注:如果在$elemMatch表达式中仅指定一个条件，则无需使用$elemMatch.

Side note: If you specify only a single condition in the $elemMatch expression, you do not need to use $elemMatch.

这篇关于如何根据另一个属性选择一个属性-mongodb的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！