Question
Lazy loading in Entity Framework is the default phenomenon that happens for loading and accessing the related entities. However, eager loading is referred to the practice of force-loading all these relations. I have come across the question of under what situation eager loading could be more beneficial than lazy loading. Asking this, because it is obvious that lazy loading is more resource friendly, and even if we use the ToList() method, we can still take advantage of the lazy loading behavior. However, I thought maybe lazy loading increases the number of requests to the actual database and maybe that's why sometimes developers use the Inlcude method to force-loading all relations. For example, when using the Visual Studio auto-scaffolding in MVC 5, the Index method that is automatically created in the controller always uses Eager Loading, and I've always had the question of why Microsoft uses Eager Loading by default in that case.
I would appreciate if someone explains to me under what situation eager loading would be more beneficial than lazy loading, and why do we use it at all while there's something more resource friendly as Lazy Loading.
Accepted Answer
I think it is good to categorize relations like this
When to use eager loading
- In "one side" of one-to-many relations that you sure are used every where with main entity. like User property of an Article. Category property of a Product.
- Generally When relations are not too much and eager loading will be good practice to reduce further queries on server.
When to use lazy loading
- Almost on every "collection side" of one-to-many relations. like Articles of User or Products of a Category
- You exactly know that you will not need a property instantly.
Note: like Transcendent said there may be disposal problem with lazy loading.
Popular Answer
Eager Loading: Eager Loading helps you to load all your needed entities at once. i.e. related objects (child objects) are loaded automatically with its parent object.
When to use:
- Use Eager Loading when the relations are not too much. Thus, Eager Loading is a good practice to reduce further queries on the Server.
- Use Eager Loading when you are sure that you will be using related entities with the main entity everywhere.
Lazy Loading: In case of lazy loading, related objects (child objects) are not loaded automatically with its parent object until they are requested. By default LINQ supports lazy loading.
When to use:
- Use Lazy Loading when you are using one-to-many collections.
- Use Lazy Loading when you are sure that you are not using related entities instantly.
NOTE: Entity Framework supports three ways to load related data - eager loading, lazy loading and explicit loading.
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