mongodb - 同一架构中的引用字段

Question

是否可以在同一架构中引用字段？请参阅下面的示例。还是我走错了路？

var UserSchema = new mongoose.Schema ({
    username: String,
    password: String,
    email: String,
    foods: [{
      name: String,
      category: String,
      ingredients: // how to reference values in the ingredients array?
    }], 
    ingredients: [{
      name: String,
      category: String
    }]  
});

Answer 1

简答

这是一个核心 MongoDB 设计决策:MongoDB relationships: embed or reference?

存储对对象的引用，而不是它们的独立副本，就像您在关系数据库中所做的那样，在 MongoDB 中是可能的，而且经常这样做，当您需要查找它们时，它只会导致越来越复杂的查询。

长答案

如果目标只是保持成分模式的定义一致，您可以定义一个模式并使用它两次。成分将作为独立副本存储，例如

[{  username: 'bob', 
    ingredients: [  { name: 'Carrot', category: 'Vegetable' } , ...],
    foods:  [ { name: 'Salad', category: 'Lunch', ingredients: [ { name: 'Carrot', category: 'Vegetable'}, ...]}]
}, ...]


var IngredientSchema = new mongoose.Schema({
  name: String,
  category: String,
});


var UserSchema = new mongoose.Schema ({
    username: String,
    password: String,
    email: String,
    foods: [{
      name: String,
      category: String,
      ingredients: [IngredientSchema] // brackets indicates it's an array, 
    }], 
    ingredients: [IngredientSchema]  
});

或者，您可以通过 objectId 引用成分:

var UserSchema = new mongoose.Schema ({
     username: String,
     password: String,
    email: String,
    foods: [{
      name: String,
      category: String,
      ingredients: [mongoose.Schema.Types.ObjectId] // IDs reference individual ingredients, 
    }], 
    ingredients: [IngredientSchema]  
});

通过显式定义 IngredientSchema，每个成分对象在声明时都会获得自己的 ObjectId。存储成分 ID(而不是成分对象的副本)的好处是更简洁和一致的存储。缺点是查询会越来越复杂。

[{  username: 'bob', 
    ingredients: [  { _id: ObjectId('a298d9ef898afc98ddf'), name: 'Carrot', category: 'Vegetable' } , ...],
    foods:  [ { name: 'Salad', category: 'Lunch', ingredients: [ {$oid: 'a298d9ef898afc98ddf'}, ]}]
}, ...]

如果您想存储对 Ingredients 的引用，更好的方法可能是将 Ingredients 存储为自己的一级集合。当您想要按成分查找食物或按食物查找成分时，您仍然会有许多单独的查询，但查询会更简单。

var UserSchema = new mongoose.Schema ({
     username: String,
     password: String,
     email: String,
     foods: [{
      name: String,
      category: String,
      ingredients: [mongoose.Schema.Types.ObjectId] // IDs reference individual ingredients, 
    }], 
    ingredients: [mongoose.Schema.Types.ObjectId]  
});

如果目标是存储对成分的规范化引用并根据它们搜索食物，引用另一篇 [SO 帖子][1]，“这是关系数据库真正大放异彩的案例之一”

请参阅此 SO 帖子以按 Id 查询子文档: Reading categories and number of articles in a single query

正如一位受访者所说，“这是关系数据库真正发挥作用的案例之一”