>>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.
>
>I'm not sure I follow that hierarchy. To me the EF/DataLayer should be the lowest level. If you need a separate Model layer then I would think that would sit above and reference the DataLayer. Personally, I find I can use the EF Entities (with perhaps some added bits in partial classes) as the Model - no need for an additional layer.
>>
>>The question is this...
>> at
>>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? .
>
>In geneal I don't think there is a 'right' way. If you know, for example, that you will need the associated Invoice Headers when you load the Customer then eager load using .Include - otherwise lazy load.


With Linq To Sql I was calling a method from the property to get back the InvoiceHeader object that belongs there:

CustomerModel retVal = (from c in context.tblCustomers
                            where c.CustomerId == CustomerId
                            select new CustomerModel
                            {
                                CustomerId = c.CustomerId,
                                CustomerName = c.CustomerName,
                                InvoiceHeader = getInvoicesForCustomer(c.CustomerId)
                            }).FirstOrDefault();

Then I changed the DL to EF and now it's not so easy. There's got be a way to do this easily.