I have Customers, Invoice Headers, Invoice Details, and Products. All are one-to-many relationships.

My solution has a data layer project built using entity framework. I also have a models project with models for each entity. The data layer project references the models project.

So far, pretty typical.

The question is this...

Here is the CustomerModel:

public class CustomerModel : _ModelBase
{
    public int CustomerId { get; set; }
    public string CustomerName { get; set; }
    public List<InvoiceHeaderModel> InvoiceHeaders { get; set; }
}

I have this GetCustomer method on the DataLayer class:

public static CustomerModel GeCustomer(int CustomerId)
{
    CustomerModel retVal = (from c in context.tblCustomers
                            where c.CustomerId == CustomerId
                            select new CustomerModel
                            {
                                CustomerId = c.CustomerId,
                                CustomerName = c.CustomerName
                            }).FirstOrDefault();
    return retVal;
}

The problem is in this method I did not load the InvoiceHeaders property. If I did that here, would you also then load the invoice details, and then the products?

What if all I wanted was a simple list of Customers so that I could populate a simple list?

I could use lazy loading in the models, but that requires the Models to be coupled to the data layer. If I used eager loading here, how would I get the hierarcchy of models?

What's the right way to do this? .