Entity Framework partial classes with custom attributes

asp.net c# entity-framework


How should I handle a custom property in a situation where I use partial classes with the EF-generated classes?

Here's the setup:

TimeSheet Table - this stores an employee's hours
- TimeSheetID (auto, int, PK)
- EntryDate (DateTime)
- Hours (int)
- EmployeeID (int)

EmployeeHourlyRate table - this stores an employee's current hourly rate. Historical rates are stored here as well.
- RateID (int, PK)
- EffectiveDate (int, PK)
- Rate (double)

This is a one to many relationship from TimeSheet to EmployeeHourlyRate. In order to find an Employee's rate, I would select the max effectiveDate less than the timeSheet's EntryDate.

In order to facilitate things, I've made a partial class called TimeSheet and added a new property called "Rate" to that class. What I would like to do is populate that myself from the same query that populates my collection of TimeSheets. I just know of no easy and clean way to handle this.

For example, I could do it this way:

var list = from ts in Context.TimeSheets
          select new TimeSheet() {
                 TimeSheetID = ts.TimeSheetID,
                 EntryDate = ts.EntryDate,
                 Hours = ts.Hours,
                 EmployeeID = ts.EmployeeID,
                 Rate = SomeRate   //real code has been omitted 

This in theory should work, but for some reason the EF complains at run-time that I'm re-using an entity generated class (no idea why -- it works fine if I create my own custom class). However, even if it did work, I've still got to maintain a list of fields and keep on mapping from my EF to a single class -- i.e, maintenance becomes a problem when/if I add new fields to the TimeSheet table. It is also silly to have to re-type all that info.

So my question is, how do people generally handle this scenario? Is there a way to do something in the datamodel that would be able to effectively know my join rule (about selecting the correct effective date based on my EntryDate) and handle this?

5/11/2009 10:38:34 PM

Accepted Answer

I would like to see your full LINQ query (including the 'SomeRate' code) to see exactly what you are trying to achieve, but maybe something like this could work:

WARNING: Air code.

public partial class TimeSheet
    public double Rate
        get //Calculate your rate here... e.g.
            if ((this.Employee == null) || (this.Employee.EmployeeHourlyRates.Count == 0))
                //throw an exception

            EmployeeHourlyRate maxRate;
            foreach (EmployeeHourlyRate rate in this.Employee.EmployeeHourlyRates)
                if ((rate.EffectiveDate <= this.EntryDate)
                    && ((maxRate == null) || (maxRate.EffectiveDate < rate.EffectiveDate)))
                    maxRate = rate;

            if (maxRate == null)
                //throw exception
                return maxRate.Rate;

EDIT: Adding example of eager loading to avoid database round trips.

var list = from ts in Context.TimeSheets.Include("Employee.EmployeeHourlyRate")
           where blah blah
           select ts;
5/12/2009 10:43:26 PM

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