Creating a "Goal" Tracker for an existing project - asp.net

Question

I have a current MVC project that is near enough complete for the basic aspects. The project tracks my progress throughout my running and weight loss as I find a lot of apps out there a bit bloated.
I have some basic models:
Distance:
public class Distance
{
public int Id { get; set; }
[DisplayName("Distance Run")]
public double DistanceRun { get; set; }
[DisplayName("Choose a date")]
[DataType(DataType.Date)]
[DisplayFormat(DataFormatString = "{0:dd/MM/yyyy}", ApplyFormatInEditMode = true)]
public DateTime _Date { get; set; }
[DisplayName("Any Addtional Comments")]
public String AdditionalComments { get; set; }
}
Weight:
{
public int Id{ get; set; }
[DisplayName("Current Weight")]
public double CurrentWeight { get; set; }
[DisplayName("Chose a date")]
[DataType(DataType.Date)]
[DisplayFormat(DataFormatString = "{0:dd/MM/yyyy}", ApplyFormatInEditMode = true)]
public DateTime _Date { get; set; }
[DisplayName("Any Addtional Comments")]
public String AdditionalComments { get; set; }
}
how would I go about creating a type of Goal creator for each one of these models. When I mean goal I mean "x amount run by y date"
I would try a possible Goal Model that would have fields similar to:
Goal:
public class Goal
{
public int Id { get; set; }
public virtual double goalValue { get; set; }
public DateTime dateTime { get; set; }
}
My issue lies where to differentiate whether the goal is either for DIstance run or Weight Lost/Gained. Am I on the right lines or should I reconsider and not use a model?

Answer 1

I would suggest using inheritance. Create a base class like:
public class Metric
{
[DisplayName("Chose a date")]
[DataType(DataType.Date)]
[DisplayFormat(DataFormatString = "{0:dd/MM/yyyy}", ApplyFormatInEditMode = true)]
public DateTime _Date { get; set; }
[DisplayName("Any Addtional Comments")]
public String AdditionalComments { get; set; }
}
Then, have both Distance and Weight inherit from this:
public class Distance : Metric
{
}
public class Weight : Metric
{
}
Then, your Goal can have a foreign key to Metric:
public class Goal
{
...
public virtual Metric Metric { get; set; }
}
Based on how Entity Framework handles inheritance, it will actually instantiate Distance/Weight depending on which one was actually saved. The property value will be upcasted to Metric, though, so you'll need to cast to access the properties on your derived classes:
if (goal.Metric is Distance)
{
var distanceRun = ((Distance)goal.Metric).DistanceRun;
}
You can also simply use as and then check for null:
var distance = goal.Metric as Distance;
if (distance != null)
{
// do something with `distance`
}

Answer 2

Adding an ID to a reference table that differentiates the different types is a solution to the problem. I think from an MVC-side, inheritance isn't going to work because on postback, the framework won't know what type of object to create (Distance or Weight for instance). So while inheritance may work as #Chris suggested, on the MVC side you need a composite object with some identifying value to determine which type of object is. That's where a reference table can come in handy.
OR, create a view model for the MVC side, and not load and save raw EF objects directly. Doing that adds work, but can ensure the UI design doesn't entangle the database design.