仅删除第一个表中没有与第二个表对应的条目的那些

Question

var productSchema = Schema({
product_code: String,
name: {
    type: String,
    required: true
},
description: String,
category:{
    type:  String,
    ref: 'Product_Category'
},
umo: String,
threshold: {
    type:Number,
    default: 0
},
image: String,
isactive: {
    type: Boolean,
    default: true
}
});

var product_categorySchema = Schema({
isactive: {
    type: Boolean,
    default: true
},
name: {
    type: String,
    required: true
},
description: String
});

我从类别中删除了这两个模式，但如果我在产品表中有与该类别相对应的数据，则不应删除该类别。有人可以帮忙吗？

Answer 1

它应该看起来像这样：

     // Function which delete the category behind the given _id
     async function deleteCategory(idCategory) {
        // check if there is a product related to the category
        const ret = await product_schema.findOne({
          category: idCategory,
        });

        // if there is, return an error
        if (ret) throw new Error('Cannot delete the category');

        // else do delete the category
        return product_category_schema.remove({
          _id: idCategory,
        });
      }

---

你还必须知道：

category:{
    type:  String,
    ref: 'Product_Category'
},

不是设置参考的正确方法;它应该是一个ObjectId而不是String

const {
  Schema,
} = mongoose;

category:{
    type: Schema.Types.ObjectId,
    ref: 'Product_Category'
},

Answer 2

首先，请在产品架构中更新“类别”字段的“类型”属性，如下所示：

category:{
  type:  Schema.Types.ObjectId,
  ref: 'Category' // model name
}`

并声明这样的模型：

var Product = mongoose.model('Product', productSchema );

然后使用“distinct”查询和“$ nin”查询运算符来删除产品架构未引用的类别，如下所示：

Product.find().distinct('category').then((data)=>{
   Category.deleteMany({_id: {$nin: data}}).then(del => {
       console.log("deleted",del)
   })
})