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C# : Understanding Eager Loading, Lazy Loading, and Explicit Loading in Entity Framework


Introduction

Entity Framework, a powerful Object-Relational Mapping (ORM) tool, provides developers with various loading strategies to retrieve and work with data efficiently.

In this blog, we'll delve into three key loading techniques: Eager Loading, Lazy Loading, and Explicit Loading, each serving distinct purposes in optimizing data retrieval.

Eager Loading

Eager loading is a strategy where related data is loaded from the database along with the main entity. 

This is particularly useful when you know in advance that certain related data will be needed, helping to minimize subsequent database trips.

Let's have a look at example in Entity framework core

var employees = context.Employees
                      .Include(e => e.Department)
                      .ToList();
C#
In this example, the .Include() method ensures that the Department related to each Employee is loaded eagerly.

Lazy Loading

Lazy loading defers the loading of related data until the moment it's accessed. 

This can be advantageous in scenarios where you want to minimize the initial data retrieval and only load related entities when they are explicitly accessed.

Let's have a look at example in Entity framework core

public class Employee
{
    public int EmployeeId { get; set; }
    public string EmployeeName { get; set; }
    public int DepartmentId { get; set; }

    public virtual Department Department { get; set; }
}

// Enable lazy loading in your context
public class AppDbContext : DbContext
{
    public DbSet<Employee> Employees { get; set; }
    public DbSet<Department> Departments { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseLazyLoadingProxies();
    }
}

// Usage
var employee = context.Employees.First();
var departmentName = employee.Department.DepartmentName; // Lazy loading occurs here
C#
Note: Lazy loading requires proxy creation, which is enabled through .UseLazyLoadingProxies() in Entity Framework Core.

Explicit Loading

Explicit loading is a manual approach where related data is loaded on-demand, giving developers precise control over when and what data to load. 

This is beneficial in scenarios where you want to fetch related entities based on specific conditions or user interactions.

Let's have a look at example in Entity framework core

var employee = context.Employees.First();
context.Entry(employee)
       .Reference(e => e.Department)
       .Load();
C#
In this example, .Reference() is used to load a single navigation property, and .Load() triggers the explicit loading of the Department related to the specified Employee.

Conclusion

In conclusion, Choosing the appropriate loading strategy in Entity Framework is crucial for optimizing performance and minimizing unnecessary database queries. 

Eager loading is suitable when you know upfront that certain related data will be used, lazy loading defers loading until needed, and explicit loading gives you fine-grained control over data retrieval. 

By understanding and utilizing these loading techniques in your Entity Framework applications, you can strike the right balance between performance and resource efficiency.

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