Querying a custom type with Database.SqlQuery<T> in EF Core 7.0

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05-10-2024

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Querying Custom Types with Database.SqlQuery<T> in EF Core 7.0

Problem: When working with Entity Framework Core (EF Core), you may encounter situations where you need to execute raw SQL queries that return data not directly mapped to your entities. This is especially relevant when working with legacy databases, complex data structures, or specific data retrieval needs.

Rephrased Problem: Imagine you have a database with a table containing customer information. You want to retrieve a specific set of customer data, but the required columns and structure don't perfectly align with your existing entity model. How can you query this data and map it to a custom object using EF Core?

Scenario:

Let's assume we have a table named Customers with the following structure:

CREATE TABLE Customers (
    CustomerId INT PRIMARY KEY,
    FirstName VARCHAR(50),
    LastName VARCHAR(50),
    Address VARCHAR(255),
    PhoneNumber VARCHAR(20),
    DateOfBirth DATE
);

We want to retrieve customer information along with a calculated FullName field. To achieve this, we'll create a custom type to represent the result:

public class CustomerInfo
{
    public int CustomerId { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string FullName { get; set; }
}

Now, let's see how we can use Database.SqlQuery<T> in EF Core to execute a raw SQL query and map the results to our custom type.

using Microsoft.EntityFrameworkCore;
using System.Linq;

public class CustomerContext : DbContext
{
    public DbSet<Customer> Customers { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseSqlServer("YourConnectionString");
    }
}

public class Program
{
    public static void Main(string[] args)
    {
        using (var context = new CustomerContext())
        {
            // Define the SQL query
            string sqlQuery = "SELECT CustomerId, FirstName, LastName, FirstName + ' ' + LastName AS FullName FROM Customers";

            // Execute the query and map results to CustomerInfo objects
            var customerInfos = context.Database.SqlQuery<CustomerInfo>(sqlQuery).ToList();

            // Display the results
            foreach (var customerInfo in customerInfos)
            {
                Console.WriteLine({{content}}quot;Customer ID: {customerInfo.CustomerId}, Full Name: {customerInfo.FullName}");
            }
        }
    }
}

Analysis:

• Database.SqlQuery<T> is a powerful method provided by EF Core to execute raw SQL queries.
• T represents the type of the object to which the results will be mapped.
• The SQL query string is passed as an argument to the SqlQuery method.
• EF Core automatically maps the returned columns to properties of the specified type.

Key Points:

• Database.SqlQuery<T> allows you to bypass EF Core's mapping conventions and interact directly with the database.
• It provides flexibility when working with complex queries or scenarios where you need to access data not represented in your entity model.
• However, using raw SQL queries can make your code less portable and potentially harder to maintain. It's important to balance flexibility with maintainability when deciding whether to use this method.

Additional Value:

• You can use Database.SqlQuery<T> to retrieve data from multiple tables using joins or other SQL constructs.
• The SqlQuery method supports parameterized queries, preventing SQL injection vulnerabilities.
• When using raw SQL, it's crucial to understand the underlying database structure and schema to ensure accurate mapping and data retrieval.

References and Resources:

• EF Core Documentation: Database.SqlQuery
• EF Core Documentation: Querying

Conclusion:

Database.SqlQuery<T> in EF Core 7.0 provides a flexible way to query your database with raw SQL and map the results to custom types. While it offers flexibility, it's important to consider its potential drawbacks and use it judiciously to maintain code clarity and portability.