C# Q & A


What is Entity Framework lazy loading in C#?

Entity Framework (EF) Lazy Loading is a feature that enhances the efficiency of data retrieval in your C# applications by loading related data only when it’s explicitly accessed. It is a valuable aspect of Entity Framework’s approach to handling object-relational mapping (ORM) and helps reduce the amount of data fetched from the database until it’s actually needed.


Here’s how EF Lazy Loading works:


  1. Deferred Loading: When you query the database for an entity (e.g., a record in a table), Entity Framework retrieves only that entity’s data initially. Related entities, such as navigation properties or child entities, are not loaded from the database at this stage.


  1. On-Demand Loading: Lazy Loading allows related data to be loaded on-demand. This means that when you access a navigation property, EF will transparently issue a query to the database to retrieve the associated data.


For example, consider a scenario where you have an `Order` entity with a navigation property `OrderDetails`. With Lazy Loading enabled, accessing `order.OrderDetails` will trigger a database query to fetch the order details only when you first access this property.


To enable Lazy Loading in Entity Framework, you typically use the `virtual` keyword on navigation properties. Here’s an example:

public class Order
    public int OrderId { get; set; }
    public string OrderNumber { get; set; }

    // Enable Lazy Loading for OrderDetails
    public virtual ICollection<OrderDetail> OrderDetails { get; set; }

It’s important to note that while Lazy Loading can be convenient, it should be used judiciously. Excessive Lazy Loading can lead to the infamous “N+1 query” problem, where multiple queries are executed to load related data, potentially impacting performance. To mitigate this, consider using techniques like eager loading (`.Include()`), explicit loading, or disabling Lazy Loading when it’s not needed for a particular scenario.


Entity Framework Lazy Loading in C# is a mechanism that defers the loading of related data until it’s accessed, helping improve application performance by reducing unnecessary database queries. It’s a valuable feature to optimize data retrieval in Entity Framework-powered applications.

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Experienced Backend Developer with 6 years of experience in C#. Proficient in C#, .NET, and Java.Proficient in REST web services and web app development.