How to Get Joined Table Data Entity Framework - linq

Question

I have a two models which are
public class Post
{
public int Id { get; set; }
public string Title { get; set; }
public string Description { get; set; }
public string ShortDescription { get; set; }
public string PostImage { get; set; }
public string Thumbnail { get; set; }
public DateTime CreatedDate { get; set; }
public DateTime? PublishedDate { get; set; }
public string CreatedBy { get; set; }
public virtual ICollection<Category> Categories { get; set; }
}
public class Category
{
public int Id { get; set; }
public string Name { get; set; }
public virtual ICollection<Post> Posts { get; set; }
public virtual ICollection<Tag> Tags { get; set; }
}
And that generates the CategoryPosts table.
Here is my question: I want to get data from the CategoryPosts table to calculate popular categories. How can I reach that data? And what is the best way to do that?

Answer 1

If you want the popular categories you don't need to map the juction table, you can order the Categories by the count of post:
var query=yourContext.Categories.OrderBy(c=>c.Posts.Count);
If you have disabled lazy loading then you should call the Include method before:
var query=yourContext.Categories.Include(c=>c.Posts).OrderBy(c=>c.Posts.Count);
As you can see below, the SQL code generated is using the junction table to check the count of Post that have each Category and order by that criteria:
SELECT
[Project1].[Id] AS [Id],
[Project1].[Name] AS [Name]
FROM ( SELECT
[Extent1].[Id] AS [Id],
[Extent1].[Name] AS [Name],
(SELECT
COUNT(1) AS [A1]
FROM [dbo].[PostCategories] AS [Extent2]
WHERE [Extent1].[Id] = [Extent2].[Category_Id]) AS [C1]
FROM [dbo].[Categories] AS [Extent1]
) AS [Project1]
ORDER BY [Project1].[C1] ASC
The junction table generally is mapped when you need to add an additional column (that excludes both keys of the tables you are joining). In that case you need to create two one-to-many relationships between the juction table and Post and Caterogy respectively.

Answer 2

Thanks octavio ,
I got the idea right now i can easily get like that.
public List<Category> GetPopularCategories()
{
return _categoryRepository.GetAll().OrderBy(c => c.Posts.Count).ToList();
}