猫鼬的“静态"方法与“实例"方法 [英] Mongoose 'static' methods vs. 'instance' methods

问题描述

我认为这个问题类似于这一个问题，但用语有所不同.从猫鼬4 文档:

我们也可以定义自己的自定义文档实例方法.

// define a schema
var animalSchema = new Schema({ name: String, type: String });

// assign a function to the "methods" object of our animalSchema
animalSchema.methods.findSimilarTypes = function (cb) {
  return this.model('Animal').find({ type: this.type }, cb);
}

现在我们所有的动物实例都可以使用findSimilarTypes方法.

然后:

向模型添加静态方法也很简单.继续我们的animalSchema:

// assign a function to the "statics" object of our animalSchema
animalSchema.statics.findByName = function (name, cb) {
  return this.find({ name: new RegExp(name, 'i') }, cb);
}

var Animal = mongoose.model('Animal', animalSchema);
Animal.findByName('fido', function (err, animals) {
  console.log(animals);
});

似乎使用静态方法，每个动物实例也将具有findByName方法.架构中的statics和methods对象是什么?有什么区别，为什么我要在另一个上使用?

解决方案

statics是在模型上定义的方法. methods在文档(实例)上定义.

您可以使用静态方法，例如Animal.findByName:

const fido = await Animal.findByName('fido');
// fido => { name: 'fido', type: 'dog' }

您可能会使用实例方法，如fido.findSimilarTypes:

const dogs = await fido.findSimilarTypes();
// dogs => [ {name:'fido',type:'dog} , {name:'sheeba',type:'dog'} ]

但是您不会做Animals.findSimilarTypes()，因为动物是模型，它没有类型". findSimilarTypes需要在动物模型中不存在的this.type，只有文档实例将包含模型中定义的该属性.

类似地，您不会做fido.findByName，因为findByName需要搜索所有文档，而fido只是 a 文档.

¹好吧，从技术上讲，您可以，因为实例确实可以访问该集合( @AaronDufour 指出了这一点) >

I believe this question is similar to this one but the terminology is different. From the Mongoose 4 documentation:

We may also define our own custom document instance methods too.

// define a schema
var animalSchema = new Schema({ name: String, type: String });

// assign a function to the "methods" object of our animalSchema
animalSchema.methods.findSimilarTypes = function (cb) {
  return this.model('Animal').find({ type: this.type }, cb);
}

Now all of our animal instances have a findSimilarTypes method available to it.

And then:

Adding static methods to a Model is simple as well. Continuing with our animalSchema:

// assign a function to the "statics" object of our animalSchema
animalSchema.statics.findByName = function (name, cb) {
  return this.find({ name: new RegExp(name, 'i') }, cb);
}

var Animal = mongoose.model('Animal', animalSchema);
Animal.findByName('fido', function (err, animals) {
  console.log(animals);
});

It seems with static methods each of the animal instances would have the findByName method available to it as well. What are the statics and methods objects in a Schema? What is the difference and why would I use one over the other?

解决方案

statics are the methods defined on the Model. methods are defined on the document (instance).

You might use a static method like Animal.findByName:

const fido = await Animal.findByName('fido');
// fido => { name: 'fido', type: 'dog' }

And you might use an instance method like fido.findSimilarTypes:

const dogs = await fido.findSimilarTypes();
// dogs => [ {name:'fido',type:'dog} , {name:'sheeba',type:'dog'} ]

But you wouldn't do Animals.findSimilarTypes() because Animals is a model, it has no "type". findSimilarTypes needs a this.type which wouldn't exist in Animals model, only a document instance would contain that property, as defined in the model.

Similarly you wouldn't¹ do fido.findByName because findByName would need to search through all documents and fido is just a document.

¹Well, technically you can, because instance does have access to the collection (this.constructor or this.model('Animal')) but it wouldn't make sense (at least in this case) to have an instance method that doesn't use any properties from the instance. (thanks to @AaronDufour for pointing this out)

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