Get list on basis of dropdownlist data in asp.net mvc3 - asp.net-mvc-3

Question

I have two dropdownlists in my module.
In one dropdownlist, I have hardcoded all the operators like <,>,<=,>=,==
In second dropdownlist, I have hardcoded salary of employees like 1000,2000,3000,4000....50000
Now if I select < from one list and 2000 from second list and click on submit button I should get list of employees who have salary less than 2000.
I want to do this in asp.net mvc3
How can I accomplish this task? Do I need to write a stored procedure for this?
I have created dropdownlist like:
viewModel.OperatorsList = new[]
{
new SelectListItem { Value = "<", Text = "<" },
new SelectListItem { Value = ">", Text = ">" },
new SelectListItem { Value = "<=", Text = "<=" },
new SelectListItem { Value = ">=", Text = ">=" },
new SelectListItem { Value = "==", Text = "==" }
};
viewModel.SalaryList = new[]
{
new SelectListItem { Value = "1000", Text = "1000" },
new SelectListItem { Value = "2000", Text = "2000" },
new SelectListItem { Value = "3000", Text = "3000" },
// and so on
};
and I have used this to show dropdownlist in view:
<%: Html.DropDownListFor(x => x.Operators, Model.OperatorsList)%>

Answer 1

well, you could do something like that
assuming viewModel is... your viewModel, and you've got an entity Employee with a property Salary (int in this sample, it's probably a decimal in real world)
create a static helper class
public static class MyHelper
{
// a dictionary for your operators and corresponding ExpressionType
public static Dictionary<string, ExpressionType> ExpressionTypeDictionary = new Dictionary<string, ExpressionType>
{
{"<", ExpressionType.LessThan},
{">", ExpressionType.GreaterThan},
{">=", ExpressionType.GreaterThanOrEqual}
//etc
};
//a method to filter your queryable
public static IQueryable<Employee> FilterSalary(this IQueryable<Employee> queryable, int salary, string operatorType)
{
//left part of the expression : m
var parameter = Expression.Parameter(typeof(Employee), "m");
//body is the right part of the expression : m
Expression body = parameter;
//m.Salary
body = Expression.Property(body, "Salary");
//m.Salary <= 1000 (for example)
body = Expression.MakeBinary(ExpressionTypeDictionary[operatorType], body, Expression.Constant(salary));
//m => m.Salary <=1000
var lambda = Expression.Lambda<Func<Employee, bool>>(body, new[] { parameter });
//so it will be queryable.Where(m => m.Salary <= 1000)
return queryable.Where(lambda);
}
}
usage
var queryable = context.All<Employee>();//or something like that, returning an IQueryable<Employee>
queryable = queryable.FilterSalary(viewModel.Salary, viewModel.Operators);