Be Careful When Combining Distinct() And OrderBy() in EF Core Queries

Distinct&OrderBy

When working with Entity Framework Core (EF Core), developers often rely on LINQ queries to retrieve and manipulate data from the database. However, certain behaviors in EF Core can catch even experienced developers off guard, particularly when combining OrderBy or OrderByDescending with Distinct.

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This article explores how EF Core handles these operations, highlights the problems you might encounter, and provides solutions to ensure you achieve the desired results.

Understanding the Problem

When you use both OrderBy and Distinct in a query, the placement of these operations in your LINQ expression matters significantly. If you apply OrderBy before Distinct, EF Core's query translation will ignore the OrderBy clause, resulting in unsorted results. Conversely, if you place OrderBy after Distinct, the sorting will work correctly.

Why Does This Happen?

The root cause of this behavior lies in how EF Core translates LINQ expressions into SQL queries. The Distinct operator instructs EF Core to select unique records. However, depending on its placement in the LINQ query, it may…