Tips & Tricks for Working with Dapper in .NET Core

Tips & Tricks for Working with Dapper in .NET Core

Dapper is a lightweight ORM that is simple and efficient, but like any tool, there are advanced features and best practices to ensure you use it effectively. This article explores some of Dapper's advanced features and common pitfalls developers should be aware of.

 

Advanced Features in Dapper

MultiMapping

Dapper allows you to map multiple result sets to multiple objects with its MultiMapping feature. This is particularly useful when working with joins or complex queries where you need to map different tables to different classes.

Example:

var sql = @"

    SELECT

        e.Id, e.Name, e.Email,

        d.Id AS DepartmentId, d.Name AS DepartmentName

    FROM Employees e

    INNER JOIN Departments d ON e.DepartmentId = d.Id";

 

using (var connection = new SqlConnection(connectionString))

{

    var result = connection.Query<Employee, Department, Employee>(

        sql,

        (employee, department) =>

        {

            employee.Department = department;

            return employee;

        },

        splitOn: "DepartmentId"

    ).ToList();

}

In the example, the splitOn parameter tells Dapper where to split the results into multiple objects (in this case, Employee and Department).

QueryAsync

Dapper supports asynchronous queries using the QueryAsync method, which is great for improving the scalability and responsiveness of your application, especially when you're dealing with multiple I/O-bound operations.

Example:

public async Task<List<Employee>> GetEmployeesAsync()

{

    using (var connection = new SqlConnection(connectionString))

    {

        string query = "SELECT * FROM Employees";

        var employees = await connection.QueryAsync<Employee>(query);

        return employees.ToList();

    }

}

Using QueryAsync allows you to avoid blocking threads while waiting for data from the database, making your application more responsive.

ExecuteScalar

The ExecuteScalar method is useful when you need to return a single value from a query, such as when counting records, summing a column, or getting a single column's value.

Example:

public async Task<int> GetEmployeeCountAsync()

{

    using (var connection = new SqlConnection(connectionString))

    {

        string query = "SELECT COUNT(*) FROM Employees";

        return await connection.ExecuteScalarAsync<int>(query);

    }

}

ExecuteScalar is efficient for queries where you only need a single value, like an aggregate or count query.

 

Common Pitfalls and How to Avoid Them

1. Forgetting to Parameterize Queries

One of the most important practices when working with Dapper is always using parameterized queries. Not parameterizing queries can lead to SQL injection vulnerabilities.

Bad Practice:

var sql = "SELECT * FROM Employees WHERE Name = '" + name + "'";

Good Practice:

var sql = "SELECT * FROM Employees WHERE Name = @Name";

var employees = connection.Query<Employee>(sql, new { Name = name });

2. Not Handling Nulls Properly

Dapper doesn't automatically handle nulls for reference types, and if a column in the database contains a null, you'll encounter issues unless you account for it.

Solution: Make sure your model types handle nulls gracefully. For example, use nullable types (int?, DateTime?) for columns that can be null.

3. Overloading Queries with Complex Logic

While Dapper is flexible, it's important not to overcomplicate queries. If your SQL logic becomes too complex, it can make your code hard to maintain and debug.

Solution: Consider breaking down your queries into smaller pieces or even using stored procedures for complex operations. This keeps your application clean and your SQL more maintainable.

4. Forgetting to Dispose of Connections

Dapper does not manage connections on its own. Make sure to always dispose of the connection after use to avoid connection leaks.

Solution: Use the using statement to automatically handle connection disposal:

using (var connection = new SqlConnection(connectionString))

{

    // Perform your query

}

 

Conclusion

Dapper is an incredibly efficient tool for data access in .NET Core, but it's important to know how to leverage its advanced features and avoid common mistakes. By utilizing features like MultiMapping, QueryAsync, and ExecuteScalar, you can make your application more efficient and responsive. Additionally, being mindful of common pitfalls, such as forgetting to parameterize queries and improperly handling null values, will help you avoid issues down the road.

Keep these tips in mind to become a more effective Dapper user and ensure your data access layer remains clean, secure, and performant.