What does Include do in LINQ

Question

I tried to do a lot of research but I m more of a db guy - so even the explanation in the MSDN doesn t make any sense to me  Can anyone please explain  and provide some examples on what Include   statement does in the term of SQL query

User · Accepted Answer

Let s say for instance you want to get a list of all your customers   var customers   context Customers ToList      And let s assume that each Customer object has a reference to its set of Orders  and that each Order has references to LineItems which may also reference a Product   As you can see  selecting a top-level object with many related entities could result in a query that needs to pull in data from many sources   As a performance measure  Include   allows you to indicate which related entities should be read from the database as part of the same query   Using the same example  this might bring in all of the related order headers  but none of the other records   var customersWithOrderDetail   context Customers Include  Orders   ToList      As a final point since you asked for SQL  the first statement without Include   could generate a simple statement   SELECT   FROM Customers    The final statement which calls Include  Orders   may look like this   SELECT   FROM Customers JOIN Orders ON Customers Id   Orders CustomerId

User · Answer

I just wanted to add that  quot Include quot  is part of eager loading  It is described in Entity Framework 6 tutorial by Microsoft  Here is the link  https   docs microsoft com en-us aspnet mvc overview getting-started getting-started-with-ef-using-mvc reading-related-data-with-the-entity-framework-in-an-asp-net-mvc-application  Excerpt from the linked page   Here are several ways that the Entity Framework can load related data into the navigation properties of an entity  Lazy loading  When the entity is first read  related data isn t retrieved  However  the first time you attempt to access a navigation property  the data required for that navigation property is automatically retrieved  This results in multiple queries sent to the database     one for the entity itself and one each time that related data for the entity must be retrieved  The DbContext class enables lazy loading by default  Eager loading  When the entity is read  related data is retrieved along with it  This typically results in a single join query that retrieves all of the data that s needed  You specify eager loading by using the Include method  Explicit loading  This is similar to lazy loading  except that you explicitly retrieve the related data in code  it doesn t happen automatically when you access a navigation property  You load related data manually by getting the object state manager entry for an entity and calling the Collection Load method for collections or the Reference Load method for properties that hold a single entity   In the following example  if you wanted to load the Administrator navigation property  you d replace Collection x   gt  x Courses  with Reference x   gt  x Administrator    Typically you d use explicit loading only when you ve turned lazy loading off  Because they don t immediately retrieve the property values  lazy loading and explicit loading are also both known as deferred loading

User · Answer

Think of it as enforcing Eager-Loading in a scenario where you sub-items would otherwise be lazy-loading   The Query EF is sending to the database will yield a larger result at first  but on access no follow-up queries will be made when accessing the included items   On the other hand  without it  EF would execute separte queries later  when you first access the sub-items

[sql] What does Include() do in LINQ?

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