使用LINQ和Entity Framework获取延迟加载的子级集合的计数

Question

I have a class such as:

public class Category
{
    public int CategoryId { get; set; }
    [Required]
    public string Name { get; set; }
    [NotMapped]
    public int ProductCount { get; set; }
    public virtual IEnumerable<Product> Products { get; set; }
}

I have a query that currently looks like this:

context.Categories.SortBy(sortByExpression).Skip(startRowIndex).Take(maximumRows)

I need to include the ProductCount field in my category grid. Is it possible to extend this LINQ query to give me the ProductCount property without reading in the entire Product collection? I can do this in a sub query using good old SQL, but I am stumped using LINQ.

Thanks

Answer 1

Is this roughly what you are looking for:

context.Categories.SortBy(sortByExpression).Skip(startRowIndex).Take(maximumRows)
    .Select(c => new { c.CategoryId, c.Name, ProductCount = c.Products.Count() });

or have I misunderstood your question?

updated the code

Answer 2

Your question is not clear as enough but if I understood well you want the new column in result for example productCount and you did it with SQL query like below:

SELECT c.*, , (SELECT COUNT(*) FROM Products p WHERE p.categoryId = c.id) AS productCount FROM
Categories c
WHERE <Conditions>

Now you want to be able do that using linq(If your question really this), you can do it as below:

List<Category> categoryList = (from c in context.Categories let pCount = c.Products.Count() select
new { categoryId = c.CategoryId, CategoryName = c.Name, productCount = pCount})
.OrderBy([sortByExpression]).Skip([startRowIndex]).Take([maximumRows]).ToList();

Hope this help.