Lazy Loading vs Eager Loading

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

User · Answer

It is better to use eager loading when it is possible, because it optimizes the performance of your application.

ex-:

Eager loading

var customers= _context.customers.Include(c=> c.membershipType).Tolist();

lazy loading

In model customer has to define

Public virtual string membershipType {get; set;}

So when querying lazy loading is much slower loading all the reference objects, but eager loading query and select only the object which are relevant.

User · 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

User · Answer

Lazy loading will produce several SQL calls while Eager loading may load data with one  more heavy  call  with joins subqueries    For example  If there is a high ping between your web and sql servers you would go with Eager loading instead of loading related items 1-by-1 with lazy Loading

User · Answer

Eager Loading When you are sure that want to get multiple entities at a time  for example you have to show user  and user details at the same page  then you should go with eager loading  Eager loading makes single hit on database and load the related entities   Lazy loading When you have to show users only at the page  and by clicking on users you need to show user details then you need to go with lazy loading  Lazy loading make multiple hits  to get load the related entities when you bind iterate related entities

User · Answer

Using LINQ and just referencing p Employer will lazy load    I am not at a computer but I know I have lazy loaded in one    query with a single query call like below  List lt Person gt  persons   new List lt Person gt     using MyDbContext dbContext   new MyDbContext          persons             from p in dbcontext Persons         select new Person              Name   p Name              Email   p Email              Employer   p Employer            ToList

User · Answer

Consider the below situation   public class Person      public String Name get  set       public String Email  get  set       public virtual Employer employer  get  set      public List lt EF Person gt  GetPerson        using EF DbEntities db   new EF DbEntities            return db Person ToList              Now after this method is called  you cannot lazy load the Employer entity anymore  Why  because the db object is disposed  So you have to do  Person Include x  gt  x employer  to force that to be loaded

User · Answer

Lazy loading - is good when handling with pagination like on page load list of users appear which contains 10 users and as the user scrolls down the page an api call brings next 10 users Its good when you don t want to load enitire data at once as it would take more time and would give bad user experience  Eager loading - is good as other people suggested when there are not much relations and fetch entire data at once in single call to database

User · 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

[c#] Lazy Loading vs Eager Loading

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