Getting data in Entity Framework

Question

I have an Entity Framework Model in my project: enter image description here

In the past, I would use a LINQ statement to get the data about a book from both tables:

var books = (from book in db.Books
             join author in db.Authors on book.AuthorId equals author.AuthorId
             select new { book.Title, author.Name, book.Price }).ToList();

dataGridView1.DataSource = books;

As you can see, this code just joins the two tables on AuthorID and returns the results as a List.

But, now that I'm trying to use Entity Framework, I was wondering how to accomplish this same objective? I mean, since I have the relationship between the Book file and the Author file via AuthorId, isn't there a way I can just say "Give me the book data based on this model" and it will return a dataset comprised of data from both entities? I hope I'm not being obtuse, I just figured since there was an association described between the two entities, that I wouldn't have to do a join in a LINQ query to get the data. My thoughts are, the data should already be linked together, via the model and the described association. Does this make sense?

Christos · Accepted Answer · 2014-07-23 12:21:13Z

3

You could try this one:

var books = (from book in db.Books  
             select new { book.Title, book.Author.Name, book.Price }).ToList();

In other words, you can use te Navigation Properties, to do so.

answered Jul 23, 2014 at 12:21

Christos

54.1k9 gold badges82 silver badges114 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

astian Over a year ago

Cant this result in null reference exception if there is no author for the book ? Or will it just skip it ?

Askolein Over a year ago

@astian it will throw an exception. You have to test it. But if your DB schema has a NOT NULLon the foreign key, no problem, lazy loading will do the rest and no null pointer exception possible.

haim770 Over a year ago

@Christos, What makes you think that?

Kevin Over a year ago

This worked perfectly. I also removed an Author from the table, re-ran the project, and received no exception. Only a blank field for Author appeared in my datagrid. As soon as the time is up, I'll mark this as the answer.

Christos Over a year ago

@haim770 are you refer to the answer or the comment that I deleted, since I was wrong?

Collectives™ on Stack Overflow

Getting data in Entity Framework

1 Answer 1

5 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

5 Comments

Your Answer

Sign up or log in

Post as a guest

Related