Скачать или смотреть How to Successfully Add New Entities in a Database Using Spring Boot and PostMapping

This guide provides a detailed explanation of how to resolve the `PropertyValueException` in Spring Boot when adding new products with existing categories in a database using PostMapping.
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Adding New Entities in a Database with Spring Boot and PostMapping

In the world of web development, especially when working with Java and Spring Boot, managing database entities efficiently is crucial. You may find yourself running into issues, such as an org.hibernate.PropertyValueException, when your intention is to add a new product while associating it with existing categories. In this post, we'll explore a practical solution to this issue, breaking down the steps to prevent Hibernate from mistakenly trying to create a new entity instead of recognizing the existing one.

Understanding the Issue

You have two entities: Category and Product. When attempting to add a Product that should reference an already existing Category, you encounter the following error:

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This error indicates that Hibernate is trying to create a new Category instead of linking to the existing one, leading to problems with the database constraints you've defined. Specifically, the categoryName field of your Category entity is marked as nullable = false, which means it cannot accept null values.

The Solution

To resolve this problem, you need to ensure that your code properly fetches the existing Category before associating it with a new Product. Here's a step-by-step approach to implementing this solution.

Step 1: Modify Your DTOs

Start by reviewing your CategoryDto and ProductDto classes. Ensure that you have enough information to identify existing categories. For instance, keep the categoryId in your CategoryDto, which allows you to reference the category directly when creating a new product.

Step 2: Update Your Mappers

Your CategoryMapper and ProductMapper should already be able to convert between entities and DTOs. However, make sure that the mappers can handle translating the categoryId from CategoryDto back into an existing Category when creating a Product. Using the categoryId, fetch the existing Category in your service layer before saving.

Step 3: Adjust Your Controller Logic

In your create method in the controller, you need to first check if the categories associated with the ProductDto exist and then fetch them from the database:

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Step 4: Service Layer Adjustments

Ensure your service layer checks for category existence as well:

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This segment of code saves the Product with its previously fetched and associated Category entities.

Conclusion

By following these steps, you can successfully add new Product entities without encountering errors related to unidentified or transient Category entities. Remember to always ensure that your code properly checks for existing entities before attempting to create new ones, especially when dealing with relationships in your database.

Whether you are managing products, categories, or any other entities in your application, keeping these principles in mind will help you avoid runtime errors and strengthen your application's integrity.