How to Select Distinct Records with Entity Framework

When using Entity Framework (EF), you can easily retrieve distinct records from your database using LINQ. Here’s how to do it for both single and multiple columns:

• Distinct for a Single Column
  To select distinct values from a single column, use the Distinct() method:

var distinctNames = DBContext.Addresses
                             .Select(m => m.NAME)
                             .Distinct()
                             .ToList();

• Distinct for Multiple Columns
  Let’s say you want to retrieve distinct combinations of both NAME and ID from the same Addresses table. Here’s how you can do it:

using (var context = new YourDbContext())
{
 var distinctAddresses = context.Addresses
 .Select(m => new { m.NAME, m.ID })
 .Distinct()
 .ToList();
}

Explanation:

• Select(m => new { m.NAME, m.ID }): This projects the query to select both NAME and ID columns as part of an object.
• Distinct(): This ensures that only unique combinations of NAME and ID are returned.
• ToList(): Converts the result into a list.

Performance Considerations
Distinct() can impact performance, especially with large datasets, as it requires sorting or comparing records to remove duplicates. Always test and optimize queries where necessary.

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Conclusion
Using Distinct() in Entity Framework allows you to easily retrieve unique values based on one or more columns. Whether you're working with a single column or need to filter unique combinations of multiple columns, this simple method can help streamline your data queries and improve the efficiency of your application.

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Refrence

For details, check out my StackOverflow answer.