Question

I’m trying to emulate a SQL IN statement on a series of SQL LIKE statements using LINQ (C#).
I start off with a IQueryable<user> object named Query which has not yet been ‘filtered’.
I’m just starting to post onto Stack Overflow so please be patient with me :)…

ObjectQuery<user> Context = this.Context.users;
IQueryable<user> Query = (IQueryable<user>)Context;
// create a BLANK clone of the FULL list (Query)
var QueryFinal = Query.Where(i => i.ID == 0);
foreach (String Item in userFilter.Name.Contains)
{
    // based on the FULL list (Query) return all records that apply to this item & then append results to the final list
    QueryFinal = QueryFinal.Concat(Query.Where(i => i.Name.Contains(Item)));
}
return QueryFinal.ToList();

I thought that on each iteration, the result set being returned on the Query.Where statement would be appended to the QueryFinal list, which it does, but for some reason, on each subsequent iteration, it appears to overwrite all the previous records which are supposed to be ‘stored for safe-keeping’ in the final list. I’ve have also tried using .Union but still not the results I was hoping for. All it seems to return is the last result set, not all of the appended result sets together. Anyone spot what I’m doing wrong?

Answer 1

Because of deferred execution, when you call QueryFinal.ToList();, it will be using the last value of Item – this is a pretty common problem when doing these sorts of queries in a foreach loop.

In your case, something like this might help:

foreach (String Item in userFilter.Name.Contains) 
{ 
    string currentItem = Item;
    // based on the FULL list (Query) return all records that apply to this item & then append results to the final list 
    QueryFinal = QueryFinal.Concat(Query.Where(i => i.Name.Contains(currentItem))); 
}