Linq-to-SQL-分组和联接

Question

I have this schema:

Products (**ProductId**, OwnerId, Name)
Categories (**CategoryId**, Name)
ProductsInCategories( **ProductId**, CategoryId )

When I wish to return the list of categories the Linq is simple enough:

from c in db.Categories
orderby c.Name
select c;

However, I want to return only the set of categories that contain products with a specific OwnerId.

If this were normal T-SQL then I can do that easily enough:

SELECT ProductsInCategories.CategoryId
FROM ProductsInCategories
INNER JOIN Categories ON ProductsInCategories.CategoryId = ProductsInCategories.CategoryId
INNER JOIN Products   ON ProductsInCategories.ProductId  = Products.ProductId
WHERE Products.OwnerId = 3
GROUP BY ProductsInCategories.CategoryId

(But I note this SQL only returns Category IDs but not Category names as well, ideally I'd like to return both)

However when I convert this to Linq it doesn't work anymore:

from pic in db.ProductsInCategories
join p in db.Products   on pic.ProductId  equals p.ProductId
join c in db.Categories on pic.CategoryId equals c.CategoryId
orderby c.Name
where p.OwnerId == ownerId
select c;

LinqPad reports this returns a large result set that contains numerous duplicate entries (category names are repeated for each product-in-category mapping).

What's the solution here?

Thanks!

Answer 1

var q =
    from c in db.Categorie
    where (from pic in db.ProductsInCategories
          join p in db.Products on pic.ProductId equals p.ProductId
          where p.OwnerId == ownerId && pic.CategoryId == c.CategoryId
          select pic).Any()
    select c;

Answer 2

Please run this SQL Statement.If you get true result,we can convert it to Linq 2 sql together

SELECT CategoryId, Name
FROM Categories
WHERE CategoryId IN (SELECT CategoryId FROM ProductsInCategories PIC
                     INNER JOIN Products P ON PIC.ProductId = P.ProductId
                     WHERE P.OwnerID = @OwnerID)