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Using Dapper Multi-Mapping to Resolve the N+1 Problem

Explore how to apply Dapper's multi-mapping feature to efficiently retrieve related data in a single query, resolving the N+1 problem. This lesson helps you improve API performance by mapping tabular results into hierarchical data structures, understand the use of the splitOn parameter, and optimize data retrieval in your ASP.NET Core applications.

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Wouldn't it be great if we could get the questions and answers in a single database query and then map this data to the hierarchical structure that we require in our data repository? Well, this is exactly what we can do with a feature called multi-mapping in Dapper. Let's look at how we can use this. Follow these steps:

  1. In the data repository, let's change the implementation of the GetQuestionsWithAnswers method to call a single stored procedure:

JavaScript (JSX)
public IEnumerable<QuestionGetManyResponse>
  GetQuestionsWithAnswers()
{
  using (var connection = new
   SqlConnection(_connectionString))
  {
    connection.Open();
    return connection.Query<QuestionGetManyResponse>(
        "EXEC dbo.Question_GetMany_WithAnswers");
  }
}

This is a good start but the ...