猫鼬“静态"方法与“实例"方法

问题描述

我相信这个问题类似于这个问题 但术语不同.来自猫鼬 4 文档:

我们也可以定义自己的自定义文档实例方法.

//定义一个模式var AnimalSchema = new Schema({ name: String, type: String });//为我们的animalSchema 的methods"对象分配一个函数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有一个可用的 findSimilarTypes 方法.

然后:

向模型添加静态方法也很简单.继续我们的动物架构:

//为我们的animalSchema 的statics"对象分配一个函数AnimalSchema.statics.findByName = 函数(名称，cb){return this.find({ name: new RegExp(name, 'i') }, cb);}var Animal = mongoose.model('Animal',animalSchema);Animal.findByName('fido', function (err, 动物) {控制台日志(动物)；});

似乎使用静态方法，每个动物实例也可以使用 findByName 方法.Schema 中的 statics 和 methods 对象是什么?有什么区别，为什么我要使用一个而不是另一个?

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 =>{名称:'fido'，类型:'狗'}

你可能会使用一个方法，比如fido.findSimilarTypes:

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

但你不会做 Animals.findSimilarTypes() 因为 Animals 是一个模型，它没有类型".findSimilarTypes 需要一个在 Animals 模型中不存在的 this.type，只有一个文档实例会包含模型中定义的属性.

同样，您也不会¹ 执行 fido.findByName，因为 findByName 需要搜索所有文档，而 fido 只是 一个文档.

¹好吧，技术上你可以，因为实例确实可以访问集合(this.constructor 或 this.model('Animal')) 但它拥有一个不使用实例中的任何属性的实例方法是没有意义的(至少在这种情况下).(感谢 @AaronDufour 指出这一点)>

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

// 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);
}

And then:

// 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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