In the UI, there's a dropdown that takes value for parameter 'field'. It can be a specific value or 'All' is the default where all rows irrespective of 'field' value needs to be retrieved.
How do I write the Where clause in LINQ such that if user supplies a value for field column, then use it as filter otherwise grab all rows from DB?
You can use IQueryable<T> as a base for your LINQ query and append to it all you need:
Example:
string userInput = "";
using (var context = new EntityModel())
{
IQueryable<MyEntity> query = context.MyEntities;
if (!String.IsNullOrWhiteSpace(userInput))
query = query.Where(x => x.MyFilterableProperty == userInput);
return query.ToList();
}
ToList() is my way of stating it is the end of the example because the query is being executed. The example is whole as in depending on whether userInput is set or not, the query differs.