"No supported translation in SQL" Linq workaround? - linq

Question

Currently im trying to make my query short with reusable peice of code like this to check for post if it's eligible to display.
// Logic to check if post is eligible for display
public bool isEligibleForDisplay(Post n)
{
var pubDate = n.PUBLISH_DATE ?? DateTime.MinValue;
var endDate = n.END_DATE ?? DateTime.MaxValue;
var correctState = (n.STATE == PostState.Publish || n.STATE == PostState.Furture);
var dateInRange = (DateTime.Now >= pubDate && DateTime.Now <= endDate);
return correctState && dateInRange;
}
my linq look like this:
var q = from n in _db.Posts
where isEligibleForDisplay(n)
group n by n.POST_ID into g
select g.OrderByDescending(t => t.CREATE_DATE).First();
return q.Take(quantity);
I ran into "No supported translation in SQL" problem for the first time of using linq to sql, I am just wondering if there are anyway that can use as a work around for this case, which could be troublesome if I include whole lot of those checking logic into my query everytime.
I'm so looking forward for a reply. Thanks!

Answer 1

You can create a function on your SQL server called isEligibleForDisplay that does the SQL equivalence of these checkes and add that to your dbml file.
I haven't tested this, but I'm thinking the easiest would be if you create a function where you pass the values you want, rather than the whole record, and I think something like this might work:
CREATE FUNCTION isEligibleForDisplay(
#publishDate DATETIME,
#endDate DATETIME,
#state TINYINT -- correct me if i'm wrong...
) RETURNS bit
AS
BEGIN
DECLARE #return bit
DECLARE #dateStart DATETIME, #dateEnd DATETIME
SET #return = 0
SET #dateStar t= COALESCE(#publishDate, CONVERT(DATETIME, '1900-01-01'))
SET #dateEnd = COALESCE(#endDate, CONVERT(DATETIME, '9999-12-31'))
IF getdate() BETWEEN #dateStart AND #dateEnd
BEGIN
IF #state IN(1,3) -- or whatever the int representations of your enum are
SET #return = 1
END
RETURN #return
END

Answer 2

I used the extension of linq to include a method, which can actually work very fine using IQueryable.
public static IQueryable<T> getPostActive<T>(this IQueryable<T> items) where T : P015.Models.SQLModel.Post
{
// Logic to check if post is eligible for display
var now = DateTime.Now;
return items.Where(n =>
(n.STATE.Trim() == PostState.Publish || n.STATE.Trim() == PostState.Furture || n.STATE.Trim() == PostState.Draft) &&
(
((n.END_DATE ?? SqlDateTime.MaxValue.Value) >= now) &&
((n.PUBLISH_DATE ?? SqlDateTime.MinValue.Value) <= now)
)
);
}

Answer 3

How maqny records are in _db.Posts? If not much, you can do .ToList() first, and than linq will be able to use isEligibleForDisplay function.