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Discover how to set an `asynchronous default value` in your Mongoose schema, using Axios for dynamic data retrieval. Enhance your application's functionality today!
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How to Use an Asynchronous Default Value in Mongoose Schema

In the world of web development, especially when working with databases like MongoDB through Mongoose, you might encounter scenarios that require dynamic data. One common situation is needing to fetch a default value asynchronously, such as a timestamp from an external API. This problem can become tricky because Mongoose schemas are not designed to handle asynchronous default values out of the box.

In this guide, we will unravel a solution to the dilemma of setting an asynchronous default value in your Mongoose schema, using Axios to fetch the data you need.

Understanding the Problem

Imagine you have a schema for prices, and you want the date field to automatically fetch the current date and time from an API. However, the challenge arises because Mongoose's schema does not support promises within the default value. This limitation means if you attempt to set the default in an asynchronous manner, it will not work correctly.

Example Schema

Here’s an initial example of a Mongoose schema trying to fetch a date:

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This will not work as intended because the asynchronous request to fetch the date will not return a value before the document is saved.

The Solution

To tackle this issue, we need to utilize Mongoose middleware, specifically the pre('save') hook, which allows us to execute a function before saving the document. Here’s how you can set it up:

Step-by-Step Implementation

Define Your Schema: Start by defining your schema without trying to set the default date asynchronously.

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Add a Pre-Save Middleware: Use the pre('save') method to fetch the date asynchronously before the document is saved.

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Export Your Model: Don’t forget to export your model so you can use it elsewhere in your application.

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Conclusion

By structuring the schema correctly and utilizing the pre('save') middleware, you can effectively set an asynchronous default value in your Mongoose schemas. This method opens up new possibilities for working with dynamic data, particularly when interfacing with web APIs.

If you're facing challenges with similar problems, try using this technique to streamline your implementations in Mongoose. Happy coding!