Getting the Object after Saving an Object in Mongoose

In Mongoose, the popular MongoDB object modeling tool for Node.js, it's common to perform operations such as saving an object to the database and then retrieving the updated object for further processing. In this article, we'll explore how to accomplish this task using Mongoose, covering concepts such as callbacks, promises, and async/await syntax. We'll provide detailed examples and explanations to ensure a thorough understanding, even for beginners.

Understanding the Scenario

Imagine you have a Mongoose model named Product, representing products in an e-commerce application. After saving a new product to the database, you need to retrieve the saved object with its generated ID and any other default values set by Mongoose or the database.

1. Using Callbacks
   
2. Using Promises
   
3. Using async/await

1. Using Callbacks

Callbacks are a traditional way of handling asynchronous operations in JavaScript. When saving an object in Mongoose, you can pass a callback function to the save() method to handle the result.

Example:

const newProduct = new Product({ name: "Example Product", price: 99.99 });

newProduct.save((err, savedProduct) => {
  if (err) {
    console.error("Error:", err);
  } else {
    console.log("Saved Product:", savedProduct);
  }
});

Explanation:

• new Product({ name: "Example Product", price: 99.99 }): Creates a new instance of the Product model with the specified properties.
  
• save((err, savedProduct) => { ... }): Calls the save() method on the new product instance and provides a callback function to handle the result. If an error occurs during saving, err will contain the error object. Otherwise, savedProduct will contain the updated object returned from the database.

Output:

If the save operation is successful, the savedProduct object will contain the updated product with its generated ID and any other default values.

{
  "_id": "60a76429c5b9a71c7a3ea458",
  "name": "Example Product",
  "price": 99.99,
  "__v": 0
}

2. Using Promises

Mongoose supports promises, allowing for more concise and readable asynchronous code. You can use the save() method with promises and handle the result using .then() and .catch().

Example:

const newProduct = new Product({ name: "Example Product", price: 99.99 });

newProduct.save()
  .then(savedProduct => {
    console.log("Saved Product:", savedProduct);
  })
  .catch(err => {
    console.error("Error:", err);
  });

Explanation:

• newProduct.save(): Calls the save() method on the new product instance, returning a promise.
  
• .then(savedProduct => { ... }): Handles the resolved promise, with savedProduct containing the updated object returned from the database.
  
• .catch(err => { ... }): Handles any errors that occur during the save operation.

Output:

The output will be similar to the callback method, with the savedProduct object containing the updated product.

3. Using async/await

Async/await is a modern JavaScript syntax for handling asynchronous code in a synchronous-like manner. You can use async/await with Mongoose methods that return promises, such as save().

Example:

async function saveProduct() {
  try {
    const newProduct = new Product({ name: "Example Product", price: 99.99 });
    const savedProduct = await newProduct.save();
    console.log("Saved Product:", savedProduct);
  } catch (err) {
    console.error("Error:", err);
  }
}

saveProduct();

Explanation:

• async function saveProduct() { ... }: Defines an asynchronous function named saveProduct.
  
• const savedProduct = await newProduct.save(): Uses the await keyword to wait for the save() method to resolve before continuing execution. The resolved value is assigned to savedProduct.
  
• The try/catch block handles both successful and error scenarios.

Output:

The output will be similar to the previous methods, with the savedProduct object containing the updated product.

Conclusion

In Mongoose, you can easily retrieve the object after saving it to the database using callbacks, promises, or async/await syntax. Each method provides a different approach to handling asynchronous operations, allowing you to choose the one that best fits your coding style and project requirements. By understanding these concepts and practicing with examples, you'll be able to effectively manage database operations in your Node.js applications.