mongodb - 嵌套对象是否自动生成ObjectId？

Question

我的架构如下:

const MessageType = {
   // ...
   oAuth: { provider: String, id: String },
   attachments: [ {name: String, contentType: String} ],
   // ...
}
MessageSchema = new mongoose.Schema(MessageType, { timestamps: true});
Messages = mongoose.model("Message", MessageSchema);

当我使用 Messages.create 插入新的消息文档时, 一个 ObjectId ( _id ) 也为 attachments 生成, 除了我的 name和 contentType字段，即:

[ { name: "xxx", contentType: "yyy", _id: zzzzzz }]

为什么会这样，对于 attachments但不是 oAuth ？

Answer 1

为避免生成 _id，您必须设置选项 _id: false，此外，如果您不想保存空附件对象，则需要设置 default: undefined .

const MessageTypeSchema = new  mongoose.Schema({
    oAuth: {
        type: String
    },
    attachments: {
        type: [
            {
                type: String
            }
        ],
        _id: false,
        default: undefined
    }
});

这是我用来测试的代码:

 console.log('-------- Document with attachments --------');
    new MessageTypeModel({
        oAuth:'xxxxxxxxxxxxx',
        attachments: ['teste.png','teste2.jpg']
    }).save().then(result => {
        console.log(result);
    });

    console.log('-------- Document without attachments --------');
    new MessageTypeModel({
        oAuth:'xxxxxxxxxxxxx'
    }).save().then(result => {
        console.log(result);
    });

执行结果如下:

Mongoose 为单个嵌套子文档 或数组 创建_id，而您的对象字段oAuth 不是以下情况之一:

Subdocuments are documents embedded in other documents. In Mongoose, this means you can nest schemas in other schemas. Mongoose has two distinct notions of subdocuments: arrays of subdocuments and single nested subdocuments.

Each subdocument has an _id by default. Mongoose document arrays have a special id method for searching a document array to find a document with a given _id.

var childSchema = new Schema({ name: 'string' });

var parentSchema = new Schema({
  // Array of subdocuments
  children: [childSchema],
  // Single nested subdocuments. Caveat: single nested subdocs only work
  // in mongoose >= 4.2.0
  child: childSchema
});

Mongoose 文档链接:Mongoose SubDocs