Question

Okay I am trying to make a partial view and controller whose job it is to select and display a list of accessories for whatever product is currently being viewed in the parent view.

The database I am working again stores this information in a field that is formatted as a comma separated list, like this:

productnr,productnr2,productnr3,productnr4

So I use the following code to retrieve this list and use it to run the equivalent of an SQL WHERE IN statement:

[ChildActionOnly]
public ActionResult _ListAccessories(string Artnr)
{
    var List = (
        from ArtTbl in db.ArtTbl
        where ArtTbl.ArticleNr == Artnr
        select ArtTbl.AccessoryList)
        .SingleOrDefault();

    var AccList = customFunctions.Accessories(text);

    var AccQuery = 
        from Art in db.ArtTbl
        where AccList.Contains(ArtTbl.ArticleNr)
        select new AccessoryList
        {
            Artnr = ArtTbl.ArticleNr,
            Name = ArtTbl.Namefield_1,
        };

    return PartialView(AccQuery);
}

The function in the AccList variable transforms the first string into the result below. I did this because all the examples I saw used such a syntax, the function seems to work properly as I’ve tested by sending it as a viewBag to the view just to check that it looks correct:

"productnr", "productnr2", "productnr3", "productnr4"

This is what the AccessoryList model looks like as well, just a very simple model:

public class AccessoryList 
{
    public string Artnr { get; set; }
    public string Name { get; set; }

    public AccessoryList()
    {
    }
}

Now this code works, but the problem is that it is too generous, if I have a product number in the list that says “AP500W” then it will also return “AP500” or just “500”. This is a problem as it should only return the exact match.

Answer 1

The reason you’re having problems begins and ends with this:

The database I am working again stores this information in a field
that is formatted as a comma separated list

LINQ is translating this to a SQL statement that is treating the entire field value as a single entity – because it is a single entity. When Contains() is evaluated, it’s simply looking for matching substring values. That’s why AP500 and 500 match AP500W.

Since you’re really trying to do the equivalent of WHERE IN (...) you’ll need to convert your MVA (multi-valued attribute) into a set of distinct values.

The query works in your example where you send a view bag of individual string values:

"productnr", "productnr2", "productnr3", "productnr4"

Your database value is actually a single string value:

"productnr, productnr2, productnr3, productnr4"

The difference is subtle but very important. Notice in the second example there is only one string of data that acts as a single value.