How to Change Field Values Before Saving to a MongoDB Database in Node.js with Mongoose

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The Problem: Saving Data Before Modifying Field Values

Consider a scenario where you're saving reservation data for a booking system. You have a totalCost field that needs to be calculated based on the number of guests and the duration of their stay. The trouble is that as your current code stands, the data is saved before you've had a chance to modify the totalCost field appropriately. This could lead to inaccurate data in your database.

Here's the relevant part of the existing code that raises the problem:

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

The Solution: Calculate Total Cost Before Saving

To tackle the problem of modifying the totalCost value, we can shift the calculation logic directly into your POST function. Here’s how you can do that step-by-step:

Step 1: Extract Required Data

Instead of directly accessing the request body, destructure the necessary values we'll use for the calculation:

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

Step 2: Calculate the Duration of Stay

Using the parsed check-in and check-out dates, calculate the difference in days:

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

Step 3: Retrieve Room Cost

Next, obtain the room cost from the database using the room ID:

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

Step 4: Compute the Total Cost

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Step 5: Create and Save the Reservation Instance

Finally, create the Reservation instance, assigning totalCost the calculated value, and save it to the database:

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

Resulting Code

Here's how your complete POST function can look now:

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

Conclusion

If you have any questions or further issues, feel free to share! Happy coding!