ASP.NET MVC - Join Tables using LINQ

My application is structured as:

namespace DomainModel.Abstract
{
    public interface IContentItemsRepository
    {
        IQueryable<Content> ContentItems { get; }
        IQueryable<Category> Categories { get; } 
        IQueryable<ContentCategory> ContentCategories { get; }
    }
}

namespace DomainModel.Entities
{
    [Table(Name = "Content")]
    public class Content
    {
        [Column(IsPrimaryKey = true, 
              IsDbGenerated = true, 
              AutoSync = AutoSync.OnInsert)]
        public int content_id { get; set; }
        [Colu开发者_如何学JAVAmn]
        public string type { get; set; } // article, video, recipe, tool
        [Column]
        public string title { get; set; }
...

namespace DomainModel.Entities
{
    [Table(Name = "Content_Categories")]
    public class ContentCategory
    {
        [Column(IsPrimaryKey = true, 
              IsDbGenerated = true, 
              AutoSync = AutoSync.OnInsert)]
        public int content_category_id { get; set; }
        [Column]
        public int content_id { get; set; }
        [Column]
        public int category_id { get; set; }
...

namespace DomainModel.Entities
{
    [Table(Name = "Categories")]
    public class Category
    {
        [Column(IsPrimaryKey = true, 
              IsDbGenerated = true, 
              AutoSync = AutoSync.OnInsert)]
        public int category_id { get; set; }
        [Column]
        public string category_name { get; set; }
        [Column]
        public string type { get; set; } //recipe,tool,other 
        [Column]
        public int ordering { get; set; }
...

I can do this:

var articlesInCategory = _contentRepository.ContentItems
            .Where(x => x.type == "article");

and get a list of articles. No problem.

However, I now need to select Content based on categories. So, I need to join Content to ContentCategory to Category.

I have no idea how to do this. Any help will be much appreciated.

Thanks.

EDIT:

I think part of my problem is that I don't even know how to call what I'm doing, so it's hard to search for this. Am I even doing LINQ to SQL, or LINQ to Entities, or is it LINQ to Objects?

The join query will be something like this.

var content=
from category  in _contentRepository.Category
join  contentCategory in _contentRepository.ContentCategory
on category.category_id equals contentCategory.category_id 
join content in _contentRepository.Content
on content.content_id equals contentCategory.content_id
where category.category_id==@yourcategoryId 
select new {type , title  }

The concept you are looking for is called SelectMany in linq, and there are a number of ways to accomplish it.

One is:

var content = 
from category in _categoryRepository.CategoryItems
join contCat in _contentCategoryRepository.Items
on category.category_id == conCat.category_id
where category.category_id == parameter
select contCat.content_id;

From here you should be able to extend it into pulling out all the data you need...look into the into keyword and check out this link if you haven't already.