Nested Query Entity Framework - entity-framework

Question

Need help in converting below SQL nested query to a LINQ query?
select P.ProductId, P.Name, C.Name, I.Image
from Product P
join ProductImage I on P.ProductId = I.ProductId
join ProductCategory C on P.Category = C.CategoryId
where P.ProductId in (select distinct ProductId
from ProductVariantMapping M
where M.GUID in (select top 3 V.Guid
from [Order] O
join Inventory V on V.InventoryId = O.InventoryId
group by O.InventoryId, V.Guid
order by Sum(O.Quantity) desc))
Below is my attempt in converting to LINQ query :
var a = (from product in ekartEntities.Products
join productImage in ekartEntities.ProductImages
on product.ProductId equals productImage.ProductId
join category in ekartEntities.ProductCategories
on product.Category equals category.CategoryId
where product.ProductId
select new ProductDTO()
{
ProductId = product.ProductId,
Name = product.Name,
Category = category.Name,
Image = productImage.Image
}).ToList();
what is the equivalent of "IN" when converting to LINQ .
I got the solution for 'IN' clause.
But how do I use sum(Quantity) in order by after grouping?
I am new to Entity Framework. Can anyone help me?

Answer 1

In LINQ, you will need to use the "contains()" method to generate the 'IN' You need to put a list in the Contains method. If sends a query, that query will be repeated for completions and this will lead to performance loss.
Sample:
var sampleList = (from order ekartEntities.Order
join inventory in ekartEntities.Inventory on order.InventoryId equals inventory.InventoryId
select order).toList();
var query = (from product in ekartEntities.Products
join productImage in ekartEntities.ProductImages
on product.ProductId equals productImage.ProductId
join category in ekartEntities.ProductCategories
on product.Category equals category.CategoryId
where sampleList.Contains(product.ProductId)
select new ProductDTO()
{
ProductId = product.ProductId,
Name = product.Name,
Category = category.Name,
Image = productImage.Image
}).ToList();

Answer 2

Do not apply ToList() in the first query
I made some test.
Test 1 (with my own data):
var phIds = new List<string>
{
//List of Ids
};
using (var db = new ApplicationDbContext())
{
var studentsId = db.Relations
.Where(x => phIds.Contains(x.RelationId))
.Select(x => x.Id)
.Distinct(); //IQueryable here
var studentsQuery = from p in db.Students
where studentsId.Contains(p.Id)
select p;
var students= studentsQuery .ToList();
}
The generated query looks like :
SELECT
[Extent1].[Id] AS [Id],
[...]
FROM [dbo].[Students] AS [Extent1]
WHERE EXISTS (SELECT
1 AS [C1]
FROM ( SELECT DISTINCT
[Extent2].[StudentId] AS [StudentId]
FROM [dbo].[Relations] AS [Extent2]
WHERE ([Extent2].[RelationId] IN (N'ccd31c3d-dfa3-4b40-...', N'd2cb05a2-ece3-4060-...'))
) AS [Distinct1]
WHERE [Distinct1].[StudentId] = [Extent1].[Id]
)
The query looks exactly like I wanted
However, if you add the ToList() in the first query to get the ids, you no longer have an IQueryable but a list.
Test 2 : wrong (I added ToList):
var phIds = new List<string>
{
//List of Ids
};
using (var db = new ApplicationDbContext())
{
var studentsId = db.Relations
.Where(x => phIds.Contains(x.RelationId))
.Select(x => x.Id)
.Distinct().ToList(); // No longer IQueryable but a list of 3000 int
var studentsQuery = from p in db.Students
where studentsId .Contains(p.Id)
select p;
var students= studentsQuery .ToList();
}
The generated query is ugly:
SELECT
[Extent1].[Id] AS [Id],
[...]
FROM [dbo].[Patients] AS [Extent1]
WHERE [Extent1].[Id] IN (611661, 611662, 611663, 611664,....
//more than 3000 ids here
)