Question

I’m trying to convert some old code that directly builds SQL queries to Entity Framework, and came across a problem that many seem to have (judging from the large number of questions surround that topic): how to express dynamic where conditions in linq.

How could I express the following code with a linq query:

    switch (status) {
        case "0":
            sqlwhere = " WHERE status < 0 ";
            break;
        case "-1":
            sqlwhere = " WHERE status = -1 ";
            break;
        case "-100":
            sqlwhere = " WHERE status = -100 ";
            break;
        case "1":
        default:
            sqlwhere = " WHERE status >= 0 ";
            break;
    }

    if (strsearch != "")
        sqlwhere += " AND desc LIKE '%" + strsearch + "%' ";

    string sqlc = "SELECT top 10 * FROM c " + sqlwhere + " order by date desc";

I’ve read about PredicateBuilder and the dynamic Linq extensions in other posts, but I think that a simple case like could be solvable without external libraries.

Using .net 4.5, EF 5.0, C#, can this be done in a “dynamic” way without building the complete linq statement for each single case?

Answer 1

If you don’t want to use something external, then simply use fluent API:

var query = db.YourTableName
              .Where(x => x.desc.Contains(strsearch));

switch (status) {
   case "0":
        query = query.Where(x => x.status < 0);
        break;
   case "-1":
        query = query.Where(x => x.status == -1);
        break;
   case "-100":
        query = query.Where(x => x.status == -100);
        break;
   case "1":
   default:
        query = query.Where(x => x.status >= 0);
        break;
}

var result = query.OrderByDescending(x => x.date)
                  .Take(10);

BTW You can create extension method for filtering by status. And your query will look like:

var query = db.YourTableName
              .FilterByStatus(status)
              .Where(x => x.desc.Contains(strsearch))
              .OrderByDescending(x => x.date)
              .Take(10);

Extension method:

public static IQueryable<YourType> FilterByStatus(this IQueryable<YourType> query, 
                                                  string status)
{

    switch (status) {
       case "0":
            return query.Where(x => x.status < 0);            
       case "-1":
            return query.Where(x => x.status == -1);
       case "-100":
            return query.Where(x => x.status == -100);
       case "1":
       default:
            return query.Where(x => x.status >= 0);
    }
}