Linq distinct record containing keywords

Question

I need to return a distinct list of records based on a car keywords search like: \"Alfa 147\"

The problem is that, as I have 3 \"Alfa\" cars, it returns 1 + 3 records (i

Answer 1

One of the beautiful features of linq is that you can build up complicated queries in smaller and simpler steps and let linq figure out how to join them all together.

The following is one way to get this information. I'm not sure whether this is the best and you would need to check it performs well when multiple keywords are selected.

Assuming keywords is defined something like

var keywords = "Alfa 147";
var splitKeywords = keywords.Split(new char[] {' '});

Stage 1

Get a list of keywords grouped by Ad and Category and

var subQuery = (from kac in keywordAdCategoryQuery  
    join k in keywordQuery  on kac.Keyword_Id equals k.Id 
    select new 
    {        
        kac.Ad_Id, 
        kac.Category_Id, 
        KeyWord = k.Name, 
    }); 

var grouped = (from r in subQuery 
    group r by new { r.Ad_Id, r.Category_Id}  into results
    select new 
    { 
        results.Key.Ad_Id , 
        results.Key.Category_Id , 
        keywords = (from r in results select r.KeyWord) 
    });

Note, the classes you posted would suggest that your database does not have foreign key relationships defined between the tables. If they did then this stage would be slightly simpler to write.

Stage 2

Filter out any groups that do not have each of the keywords

foreach(var keyword in splitKeywords)
{
    var copyOfKeyword = keyword ;   // Take copy of keyword to avoid closing over loop
    grouped = (from r in grouped where r.keywords.Contains(copyOfKeyword) select r) ;
}

Stage 3

Group by Category and count the results per category

var groupedByCategories = (from r in grouped 
    group r by r.Category_Id into results 
    join c in categoryQuery  on results.Key equals c.Id 
    select new 
    { 
        c.Id , 
        c.Name , 
        Count = results.Count()
    });

Stage 4

Now retrieve the information from sql. This should be done all in one query.

var finalResults = groupedByCategories.ToList();