Solving the Duplicate Values Issue with Dapper in ASP.NET Core

Learn how to resolve duplicate values returned from a stored procedure using Dapper in ASP.NET Core, and streamline your data retrieval process.
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Understanding and Fixing the Duplicate Values Issue in Dapper

When working with ASP.NET Core and Dapper, you may encounter a frustrating issue where a stored procedure returns duplicate values. This can confuse developers and lead to higher data processing costs or UX issues on the front end. In this guide, we will not only address how to diagnose the problem but also provide a clear solution you can implement right away.

The Problem at a Glance

Imagine that you have a database with a total of 30 unique records. However, you're calling a stored procedure that is expected to return a pageable list of those records, but instead, you encounter a series of duplicate values. This situation can be particularly troublesome, causing the application to display incorrect or misleading information.

Example Scenario

Here’s the code snippet that illustrates this situation using Dapper to call a stored procedure:

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

The SQL Stored Procedure

Here is the relevant part of the stored procedure that fetches the records from the database:

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

Solution: Fixing the Duplicate Values Issue

Fortunately, there's a straightforward solution to this problem. The key is to ensure that you're executing your stored procedure correctly and defining the command type effectively.

Step 1: Define the Command Type

By explicitly defining the command type as CommandType.StoredProcedure, we inform Dapper that we are executing a stored procedure and not a regular SQL command. Here's how you can implement that in your existing code:

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

Additional Tips

Check for Duplicates in SQL: Before diving into Dapper, ensure that your SQL does not return duplicates. You can do this by using DISTINCT in your SQL query if necessary.

Pagination Logic: Double-check your pagination logic to ensure that it’s set up correctly to limit and fetch data appropriately.

Debugging: Add logging or debugging statements to examine what is returned by your stored procedure. This helps in identifying the issue more clearly.

Conclusion

Encountering duplicate values when using Dapper in your ASP.NET Core applications can be perplexing, but it is typically a matter of properly configuring your command types. By following the outlined solution and suggestions, you can easily resolve this issue and ensure your application behaves as expected.

Feel free to share your thoughts or any additional queries related to this topic in the comments section below!