Question

I need to query database and filter based on parameters passed into the function. I am passing two date parameters (used as a date range), a name, and a status parameters. All the parameters can have ‘and’ or ‘or’ conditions. Basically, I would like to build an linq expression based on which parameters are populated and pass it to Entity Framework to return a result set.

How can I do this with minimum ‘if’ statements? If you could be kind enough to provide an explanation with your example code, that would be awesome. I am trying to learn expression trees so an explanation would help.

At this point I don’t have much code. That is why I have posted here. I can list the method signature. What exactly are you looking for?

public enum EmployeeStatus
{
    FullTime,
    PartTime,
    Contract
}

public IEnumerable<Employee> FilterEmployees(DateTime? startDate, 
    DateTime? endDate, string employeeName, EmployeeStatus employeeStatus)
{   }

Answer 1

public IQueryable<Employee> FilterEmployees(IQueryable<Employee> query, DateTime? startDate, DateTime? endDate, string employeeName, EmployeeStatus employeeStatus)
{
    if (startDate != null)
        query = query.Where(x => x.StartDate >= startDate);

    // etc...

    return query;
}