Resolving the Column 'location_id' cannot be null Error in Spring Boot Applications

Learn how to fix the `location_id` cannot be null error when mapping a Person entity with a Location in a Spring Boot application.
---

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: I can not mapped Model and DTO could not execute statement; SQL [n/a] constraint [null]

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Understanding the Issue: Column 'location_id' cannot be null

If you are working with Java's Spring Boot framework and dealing with database interactions, you might encounter an error that says `Column 'location_id' cannot be null. This often arises when you're trying to save an entity that has a foreign key relationship with another entity in your database. In this guide, we'll unpack this problem and provide a clear solution to solve it effectively.

The Scenario

Let's say we have two entities in our application: Person and Location. The Person entity has a many-to-one relationship with Location, meaning that each person is associated with a specific location. Here's how those entities are structured:

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

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

Now, you might want to save a Person entity that includes the ID of the associated Location. Your Data Transfer Object (DTO) that should carry this information looks like this:

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

However, when making a POST request with Postman, you face the daunting error stating that the column related to location cannot be null despite having the corresponding location ID in the database.

Break Down of the Problem

The error occurs because there’s a mismatch between the types in your PersonDTO and your Person entity. Specifically, in your PersonDTO, the location field is a Long, while in your Person entity, it’s of type Location. When attempting to persist the Person object, Hibernate tries to insert a null location_id because it is unable to map the Long type directly to the Location entity.

Solution: Correct Mapping of DTO and Entity

To resolve the issue, you need to modify your PersonDTO class to match the expected type in the Person entity. Here’s how you can do it:

Step 1: Update the PersonDTO

Change the location variable in PersonDTO from Long to Location:

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

Step 2: Modify the Postman Request

Update your Postman request to reflect this change properly. Instead of passing just the ID of the location, you’ll now pass a complete Location object with an id attribute:

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

Step 3: Ensure Consistency in Variable Names and Types

As you make these changes, ensure that all corresponding field names and data types are consistent across your DTO and entity classes. It’s crucial for proper data mapping and execution without any constraints violations.

Conclusion

By making these adjustments, you’ll fix the location_id cannot be null error and ensure that your Person entity can successfully reference its associated Location. Always remember to check the data types and variable names when working with mapping in Spring Boot applications.

Good luck, and happy coding!