- Jan 2024
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mongoosejs.com mongoosejs.com
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Instance methods Instances of Models are documents. Documents have many of their own built-in instance methods. We may also define our own custom document instance methods. // define a schema const animalSchema = new Schema({ name: String, type: String }, { // Assign a function to the "methods" object of our animalSchema through schema options. // By following this approach, there is no need to create a separate TS type to define the type of the instance functions. methods: { findSimilarTypes(cb) { return mongoose.model('Animal').find({ type: this.type }, cb); } } }); // Or, assign a function to the "methods" object of our animalSchema animalSchema.methods.findSimilarTypes = function(cb) { return mongoose.model('Animal').find({ type: this.type }, cb); }; Now all of our animal instances have a findSimilarTypes method available to them. const Animal = mongoose.model('Animal', animalSchema); const dog = new Animal({ type: 'dog' }); dog.findSimilarTypes((err, dogs) => { console.log(dogs); // woof }); Overwriting a default mongoose document method may lead to unpredictable results. See this for more details. The example above uses the Schema.methods object directly to save an instance method. You can also use the Schema.method() helper as described here. Do not declare methods using ES6 arrow functions (=>). Arrow functions explicitly prevent binding this, so your method will not have access to the document and the above examples will not work.
Certainly! Let's break down the provided code snippets:
1. What is it and why is it used?
In Mongoose, a schema is a blueprint for defining the structure of documents within a collection. When you define a schema, you can also attach methods to it. These methods become instance methods, meaning they are available on the individual documents (instances) created from that schema.
Instance methods are useful for encapsulating functionality related to a specific document or model instance. They allow you to define custom behavior that can be executed on a specific document. In the given example, the
findSimilarTypes
method is added to instances of theAnimal
model, making it easy to find other animals of the same type.2. Syntax:
Using
methods
object directly in the schema options:javascript const animalSchema = new Schema( { name: String, type: String }, { methods: { findSimilarTypes(cb) { return mongoose.model('Animal').find({ type: this.type }, cb); } } } );
Using
methods
object directly in the schema:javascript animalSchema.methods.findSimilarTypes = function(cb) { return mongoose.model('Animal').find({ type: this.type }, cb); };
Using
Schema.method()
helper:javascript animalSchema.method('findSimilarTypes', function(cb) { return mongoose.model('Animal').find({ type: this.type }, cb); });
3. Explanation in Simple Words with Examples:
Why it's Used:
Imagine you have a collection of animals in your database, and you want to find other animals of the same type. Instead of writing the same logic repeatedly, you can define a method that can be called on each animal instance to find similar types. This helps in keeping your code DRY (Don't Repeat Yourself) and makes it easier to maintain.
Example:
```javascript const mongoose = require('mongoose'); const { Schema } = mongoose;
// Define a schema with a custom instance method const animalSchema = new Schema({ name: String, type: String });
// Add a custom instance method to find similar types animalSchema.methods.findSimilarTypes = function(cb) { return mongoose.model('Animal').find({ type: this.type }, cb); };
// Create the Animal model using the schema const Animal = mongoose.model('Animal', animalSchema);
// Create an instance of Animal const dog = new Animal({ type: 'dog', name: 'Buddy' });
// Use the custom method to find similar types dog.findSimilarTypes((err, similarAnimals) => { console.log(similarAnimals); }); ```
In this example,
findSimilarTypes
is a custom instance method added to theAnimal
schema. When you create an instance of theAnimal
model (e.g., a dog), you can then callfindSimilarTypes
on that instance to find other animals with the same type. The method uses thethis.type
property, which refers to the type of the current animal instance. This allows you to easily reuse the logic for finding similar types across different instances of theAnimal
model.
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- Jan 2022
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blog.atomist.com blog.atomist.com
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My gut told me calling an async function from the setTimeout callback was a bad thing. Since the setTimeout machinery ignores the return value of the function, there is no way it was awaiting on it. This means that there will be an unhandled promise. An unhandled promise could mean problems if the function called in the callback takes a long time to complete or throws an error.
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github.com github.com
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but has a critical difference: the expression console.log("before 2"); does not and cannot depend on the resolved value result. The throw propagates through all chained promises, and when it stops, there is no remaining undefined behavior! No piece of code is left in an unclear state, and therefore there is no reason to crash.
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thecodebarbarian.com thecodebarbarian.com
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The power of await is that it lets you write asynchronous code using synchronous language constructs.
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- Nov 2020
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github.com github.com
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I refactored quite a bit of tarball-fetcher now to use actual Promises and asyncawait instead of passing resolve / reject callbacks around. This makes the code quite a bit easier to follow in my opinion, but let me know if anything should be changed there.
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