如何自動更新mongodb字段

Question

我有一個Category架構，我想當children字段更改時檢查其長度，如果長度等於0，則has_children應該為false ，而相反。

這是我的模型：

const category_item = new mongoose.Schema({

   //...other fields...,
   children: { type: Array, required: true, default: [] }
   has_children:  // if children length equal to 0 get false and opposite     
});

Answer 1

保持

const category_item = new mongoose.Schema({

    ...anotherFields...,
    children : {type : Array , required : true , default : []}
    has_children : {type: Boolean}
});

並添加一個預保存鈎

category_item.pre('save', function(next) {
    if (this.children && this.children.length > 0) {
        this.has_children = true;
    } else {
        this.has_children = false;
    }
    next();
});

參考： http : //mongoosejs.com/docs/middleware.html