Question

I am trying my hands on MVC 2, ADO.NET EF and POCO. I have generated my entity classes in a separate library using POCO generator.These POCO entities are used as ViewPages (Not sure if that’s the right way to design or do I need separate ViewModels classes ?)

Now, if I take case of a simple scenario where I need to add an Employee object( which is related to a Department Master), what then should be the recommended way to transfer these objects between layers.

Layered structure of the application is somewhat like this :

I have thought of various alternatives:

I have a method in the Employee Controller which is named AddEmployee() which accepts the FormCollection as parameter. Within the form collection I get posted data such as Employee Name, Age , Salary etc and the ID of the Selected Department .

1.) One way is that I can create another DTO say EmployeeDepartment DTO which will be used to map values from FormCollection as is. I can then break them at manager layer and use them to create entity objects i.e Employee Object and refer department by query similar to this:

e.Department =  Department.where(i => i.deptId == empDepDto.dept_id).first()

I am not a big fan of this and feel that every time there is a relation involved I have to add a DTO and then map it to my entity class.

2.) Second is probably the worst, i.e passing each object as parameter and then couple them in manager layer.

3.) Use POCO as is, Create a Employee Object and Deparment Object at controller layer and pass the POCO object

public void AddEmployee(FormCollection formCollection)
{
    Department d = new Deparmtent; d.id = ""; //based on the dropdown value
    d.name="" //based on the dropdown selected text;

    Employee e = new Employee; e.Name. e. sal....

    e.Department = d;

    EmployeeManager.AddEmployee(e);
}

But at manager layer I think , I still need to recreate the reference to the Department using LINQ which again is repetitive and doesn’t seems to be a clean solution.

Are there better ways of handling this ? Looking for recommendations and best practices.

Answer 1

Firstly, is there any reason you’re not using MVC version 3? There’s no major breaking changes, so may as well upgrade?

Secondly is there a reason for using FormCollection rather than the strongly typed model-binding? Just change your views to use the strongly typed HTML helpers ( like <%: Html.TextBoxFor(m => m.Property) %>), or make sure the name attributes match the property names, and have your controller receive the type, and model binding will do the rest. There’s plenty of tutorials showing this, and articles explaining it. Model binding will work with a name/value collection, like that posted as a form, or against JSON data, or you can find/write custom model binders that work against whatever wacky serialisation protocol you want.

One thing to watch though when passing the actual entity types that Entity Framework will store around, is that you have to be careful when updating existing objects, or with foreign key references to existing objects – all your objects must be attached to the right Entity Framework context. To achieve that you will often see the objects received by the controller having their properties copied to a freshly retrieved entity from a context, either manually or by an object mapper of some kind.