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Learn how to fix the `duplicate key value` error when working with Spring Boot and PostgreSQL through sequences for unique identifiers.
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Resolving Duplicate Key Value Errors in Spring Boot with PostgreSQL

When working with databases in applications, a common issue developers encounter is the dreaded duplicate key value error. This often occurs when inserting records with primary keys that already exist in the database. In this guide, we will explore how to effectively address this problem, specifically within a Spring Boot application using PostgreSQL.

The Problem

Imagine you've developed an entity for your database, as shown in the Java code below:

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You create records using a tool like Talend or via SQL queries, but suddenly you receive an error message that states:

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This error indicates that you're trying to insert a record with a primary key (N_fnc) that already exists, leading to a conflict.

Understanding the Root Cause

In this case, the key issue is how the primary key (N_fnc) is generated. By default, if you're using @ GeneratedValue(strategy = GenerationType.IDENTITY), the database generates IDs automatically. However, if you manually insert records or if your records with specific IDs are already in the database, you might end up trying to use an ID that is not available, causing a duplicate key violation.

The Solution: Using Sequences

To effectively manage unique primary keys and avoid collisions, we can use database sequences. Here’s how to implement this solution step by step:

Step 1: Create a Sequence in the Database

Using SQL, create a sequence that will generate unique ID values. You can do this by executing the following command in your PostgreSQL database:

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Step 2: Alter the Table to Utilize the Sequence

Next, inform your fnc table to use this sequence for the N_fnc column:

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Step 3: Modify Your Entity in Java

You'll need to update your entity to specify that the N_fnc field should use the new sequence generator. Here’s how your Fnc class would look after adding the necessary annotations:

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This change tells Hibernate to use the sequence generator for the ID creation process.

Step 4: Set the Sequence Maximum Value

Finally, set the current value of the sequence to the maximum value of N_fnc already in the database using:

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This command ensures that the sequence starts generating new IDs that are greater than any N_fnc currently in use.

Conclusion

By implementing a sequence in your PostgreSQL database, adjusting your entity to utilize this sequence, and resetting the sequence value, you can effectively eliminate the duplicate key value violates unique constraint error in your Spring Boot application. This solution allows your application to generate unique primary keys seamlessly, reducing the likelihood of conflicts in your database operations.

With these steps, you are well on your way to building a robust data management system that efficiently handles unique identifiers. Remember, maintaining the integrity of your database is paramount, and utilizing sequences is just one of many strategies to achieve that stability.