I have an extension method to dynamically filter Linq to Entities results using string values. It works fine until I use it to filter nullable columns. Here's my code:
public static IOrderedQueryable<T> OrderingHelperWhere<T>(this IQueryable<T> source, string columnName, object value)
{
ParameterExpression table = Expression.Parameter(typeof(T), "");
Expression column = Expression.PropertyOrField(table, columnName);
Expression where = Expression.GreaterThanOrEqual(column, Expression.Constant(value));
Expression lambda = Expression.Lambda(where, new ParameterExpression[] { table });
Type[] exprArgTypes = { source.ElementType };
MethodCallExpression methodCall = Expression.Call(typeof(Queryable),
"Where",
exprArgTypes,
source.Expression,
lambda);
return (IOrderedQueryable<T>)source.Provider.CreateQuery<T>(methodCall);
}
Here's how I use it:
var results = (from row in ctx.MyTable select row)
.OrderingHelperWhere("userId", 5);//userId is nullable column
Here's the exception I'm getting when I use this for nullable table columns:
The binary operator GreaterThanOrEqual is not defined for the types 'System.Nullable`1[System.Int32]' and 'System.Int32'
I couldn't figured this out. What should I do?
I had to convert the value type to the column type using Expression.Convert:
Expression where = Expression.GreaterThanOrEqual(column, Expression.Convert(Expression.Constant(value), column.Type));