Скачать или смотреть How to Fix Null Values in Database When Saving Contracts in Spring Boot

Discover how to resolve the issue of null values in the database when saving housing contracts using Spring Boot and Hibernate. Learn how to correctly set relationships for entities in your application.
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This video is based on the question https://stackoverflow.com/q/64143765/ asked by the user 'Blacit' ( https://stackoverflow.com/u/10957904/ ) and on the answer https://stackoverflow.com/a/64144869/ provided by the user 'Blacit' ( https://stackoverflow.com/u/10957904/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Issue: Null Values in Your Database

When working with Java and Spring Boot applications, it’s not uncommon to encounter issues where values are not saved correctly in the database. One such problem arises when you try to save a contract for a rented apartment, but end up with null values for critical identifiers, such as id_house and id_tenant. This can lead to complications in understanding which tenant is renting which apartment.

In this post, we will discuss how to solve the issue of null identifiers in your database entries, focusing on a specific use case involving contracts related to housing rentals.

The Problem at Hand

Common Symptoms

id_house and id_tenant are null in the saved contract.

The date fields save correctly, but entity relationships do not persist.

Example

Suppose you are sending a JSON object through Postman with values for id_house and id_tenant, like so:

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

Yet, upon saving this data in the database, you find that both id_house and id_tenant are null. This issue often stems from not properly managing the relationships between the entities.

Solution Overview: Properly Mapping Entities

To resolve this issue, we need to ensure that we are effectively managing entity relationships in our code. The goal is to correctly associate the House and User (Tenant) with our Contract before saving it to the database. This requires fetching the related entities based on their IDs and setting them in the Contract before saving.

Step-by-Step Solution

1. Modify the Controller Method

First, we need to update the controller method to handle the data correctly. Instead of attempting to directly map IDs from the request body into the Contract entity, you should fetch the associated House and User objects first.

Updated Controller Code

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

2. Create a DTO (Data Transfer Object)

While it's not explicitly stated in the original question, using a DTO can help in managing incoming data. A simple ContractDto class can be defined to match the incoming JSON structure:

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

3. Error Handling

With the updated code, we've also added the capability to throw an error if the House or User is not found. This makes the application more robust and helps in troubleshooting.

Conclusion: A Clean and Effective Approach

By modifying your controller method to include the necessary data-fetching logic and creating a DTO, you can eliminate the problem of null values for id_house and id_tenant. This approach ensures that your Contract entity is correctly populated before it is saved to the database.

Implementing these changes not only resolves the immediate issue but also makes your code more maintainable and clear, a crucial aspect of successful software development.

If you run into similar issues while using Spring Boot with Hibernate, make sure to double-check your entity relationships and data handling methods. Happy coding!