EF6 query that behaves strangely using contains - sql-server

Question

I have an EF6 SQL Server query that behaves strangely when it is supplied with a List<int> of IDs to use. If bookGenieCategory = a value it works. If selectedAges is empty (count = 0) all is well. If the selectedAges contains values that exist in the ProductCategory.CategoryId column, the contains fails and NO rows are returned.
Note: AllocationCandidates is a view, which works properly on its own.
CREATE VIEW dbo.AllocationCandidate
AS
SELECT
p.ProductID, p.SKU as ISBN, p.Name as Title,
pv.MSRP, pv.Price, pv.VariantID, pv.Inventory,
ISNULL(plt.DateLastTouched, GETDATE()) AS DateLastTouched,
JSON_VALUE(p.MiscText, '$.AgeId') AS AgeId,
JSON_VALUE(p.MiscText, '$.AgeName') AS AgeName
FROM
dbo.Product AS p WITH (NOLOCK)
INNER JOIN
dbo.ProductVariant AS pv WITH (NOLOCK) ON pv.ProductID = p.ProductID
LEFT OUTER JOIN
dbo.KBOProductLastTouched AS plt WITH (NOLOCK) ON plt.ProductID = p.ProductID
WHERE
(ISJSON(p.MiscText) = 1)
AND (p.Deleted = 0)
AND (p.Published = 1)
AND (pv.IsDefault = 1)
GO
Do I have a typo here or a misplaced parenthesis in the following query?
var returnList = (from ac in _db.AllocationCandidates
join pc in _db.ProductCategories on ac.ProductID equals pc.ProductID
where (bookGenieCategory == 0
|| bookGenieCategory == pc.CategoryID)
&&
(selectedAges.Count == 0 ||
selectedAges.Contains(pc.CategoryID))
orderby ac.AgeId, ac.DateLastTouched descending
select ac).ToList();

Answer 1

Firstly, I would recommend extracting the conditionals outside of the Linq expression. If you only want to filter data if a value is provided, move the condition check outside of the Linq rather than embedding it inside the condition. This is generally easier to do with the Fluent Linq than Linq QL. You should also aim to leverage navigation properties for relationships between entities. This way an AllocationCandidate should have a collection of ProductCategories:
var query = _db.AllocationCandidates.AsQueryable();
if (bookGenieCategory != 0)
query = query.Where(x => x.ProductCategories.Any(c => c.CategoryID == bookGenieCategory);
The next question is what does the selectedAges contains? There is an Age ID on the AllocationCandidate, but your original query is checking against the ProductCategory.CategoryId??
If the check should be against the AllocationCandidate.AgeId:
if (selectedAges.Any())
query = query.Where(x => selectedAges.Contains(x.AgeID));
If the check is as you wrote it against the ProductCategory.CategoryId:
if (selectedAges.Any())
query = query.Where(x => x.ProductCategories.Any(c => selectedAges.Contains(c.AgeID)));
Then add your order by and get your results:
var results = query.OrderBy(x => x.AgeId)
.ThenByDescending(x => x.DateLastTouched);
.ToList();