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Discover how to utilize `async await` for running database queries sequentially in Express Node.js, ensuring your results are fully processed before sending to the view.
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Solving the async await Problem in Express Node.js: Executing Functions Sequentially

When working with Express and Node.js, developers often encounter challenges with asynchronous code, especially when trying to run functions sequentially using async and await. One common issue is related to database queries, where the expected results are not returned before the response is sent back to the client. In this post, we will explore this problem and demonstrate how to effectively use async await to ensure that your database queries execute in the intended sequence.

Understanding the Problem

Imagine you want to perform three separate database queries to retrieve various pieces of information and then render these results to a view. However, you may find that the data sent to the view is null or incomplete. This is likely because the asynchronous nature of JavaScript isn’t being handled correctly, causing results to be sent before they are fully fetched.

Here we analyze a specific case where this issue arises:

[[See Video to Reveal this Text or Code Snippet]]

The Core Issue

The main issue in the original code is that the functions getPromoteInfo, getPromoteReview, and getLatest3reviews are designed to use callbacks instead of returning promises. await only works with promises, meaning that without them, the values returned will be undefined, leading to everything rendering as null.

Crafting a Solution

To fix this issue, you’ll need to ensure that your database functions return promises. Here’s how you can do that:

Step 1: Update Database Functions to Return Promises

Modify your database model methods to return promises instead of using callbacks. Here’s an example of how to refactor your getPromoteInfo method:

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Use await in the Express Route Handler

Now that your database methods return promises, update your express route to simply call the function:

[[See Video to Reveal this Text or Code Snippet]]

By implementing these changes, you ensure:

Sequential Execution: Each query waits for the previous one to finish before executing.

Error Handling: Errors can be caught in the try-catch block, making debugging easier.

Conclusion

Using async await effectively is crucial for managing asynchronous operations in Express. By converting your callback-based functions to return promises, you not only achieve the desired sequential execution but also improve code readability and maintainability. Always ensure your database functions are promise-compliant for seamless integration with async await.

If you follow this guide, you will be better equipped to handle asynchronous operations without running into issues of null or incomplete data being sent to your views.