扩展POCO类以使用其他上下文进行计算

Question

Consider these two POCO classes for use with EF Code First.

public class Sale 
{
    public int SaleId { get; set; }
    public DateTime Date { get; set; }
    public double Amount { get; set; }
}

public class History
{
    public int HistoryId { get; set; }
    public DateTime Date { get; set; }
    public double Total { get; set; }
}

That is all well and good, but I actually want my class to represent more when I'm using it in my application:

 public class SaleWithAllIWant
    {
        public int SaleId { get; set; }
        public DateTime Date { get; set; }
        public double Amount { get; set; }
        public double Calculation   // Read only and NOT stored in DB
        {
            get
            {
                // Obtain Total from _Context.History on Date
                // Perform Calculation
            }
        }
    }

I want to be able to use EF's beauty and be able to do something like:

gridSales.DataSource = _Context.Sales.ToList();

However Sale doesn't have all of my info. SaleWithAllIWant is not a context so I'd have to do some sort of post butchering to get everything from Sale into SaleWithAllIWant. I could use unbound columns or similar but it gets messy and starts to affect performance.

I can't just put SaleWithAllIWant in my POCO class because the Calculation requires knowledge of the History context. My DAL project (which creates the DbSets) references my Model project (which holds the POCO classes) – so the Model project can't reference the DAL to get access to the contexts as it would be a circular reference.

Is the solution to just bung it all in together and not have a separate DAL and Model project?

I suspect there is a better way I am missing. All comments much appreciated.

Answer 1

Merging DAL and Model together is definitely an option I'd consider if you're not deploying them separately.

That said, Calculation looks like a great candidate for an extension method:

public static class SaleExtensions
{
    public static double Calculation(this Sale sale)        
    {
            // Obtain Total from _Context.History on Date
            // Perform Calculation
    }
}

which could live in your DAL project. If you need any additional properties to be kept in Sale for the purpose of doing the calculation just mark them with [NotMapped] so EF would ignore them.