So I'm building an App using the Entity Framework on top of SQL Compact Edition. I didn't like the idea of using the Entites as my business objects so I've been building a layer (I've called it ObjectModel layer, prob not the best terminology) in-between that will take my plain objects, use them to populate and save the entities. And also vice versa - take entites, populate the POCOs for use as business object
Let's say I have a POCO object called Customer,
public class Customer:ICustomer
{
#region ICustomer Members
public System.Guid id {get;set;}
public string Forename {get;set;}
public string Surname { get; set; }
#endregion
}
And I want to populate this using my ObjectModel layer. I currently do this...
OM_Customer<ICustomer,Entity.Customer> customerLayer = new OM_Agent<ICustomer,Entity.Customer>();
ICustomer businessObject = customerLayer.GetById(new Guid("4a75d5a5-6f5a-464f-b4b3-e7807806f1a9"));
The OM_Customer class inherits from ObjectModelBase, which is below..
public abstract class ObjectModelBase<BllClass, EntityClass>
{
public DataStoreEntities1 db;
public EntityClass _dataObject;
public string setName;
#region POCO-ORM Mapping Functions
public EntityClass MapBLLToEntity(BllClass bllObject)
{
Mapper.CreateMap<BllClass, EntityClass>();
return Mapper.Map<BllClass, EntityClass>(bllObject);
}
public BllClass MapEntityToBLL(EntityClass entityObject)
{
Mapper.CreateMap<EntityClass, BllClass>();
return Mapper.Map<EntityClass, BllClass>(entityObject);
}
#endregion
public void Save(BllClass toAdd)
{
_dataObject = MapBLLToEntity(toAdd);
using (db = new DataStoreEntities1())
{
db.AddObject(setName, _dataObject);
db.SaveChanges();
}
}
public BllClass GetById(Guid id)
{
using (db = new DataStoreEntities1())
{
EntityClass result = (EntityClass)((object)(from c in db.CustomerSet where c.id == id select c).First());
return MapEntityToBLL(result);
}
}
}
The problem here lies with the GetById method. The Save method can be used by subclasses fine as all Entity Framework Object Contexts have the AddObject() method.
However, I wish to have a generic getById method, as all my entities will have a property called id (in the db as well, being the primary key).The problem is that the linq here...
ModelClass result = (ModelClass)((object)(from c in db.CustomerSet where c.id == id select c).First());
is specific to db.CustomerSet . I wish to have this abstract class provide the generic CRUD/Paging/'Collection Retrieval' for all my entities, but without the repetitive keystrokes, however, this simple GetById method has driven me to ask for help.
Current ideas :
Would appreciate any adivce as to how the SO community would go about solving the above.
First, I would start by questioning why you feel that using EF entities as you business entities would necessarily be a bad thing? I've done so on a number of projects and I have yet to run into any serious issues that I can't overcome.
Having said that, if you really feel you have a strong reason to separate the two, here's one option.
You can use a delegate to inject the specific entity set object to query and another for the selector for the key - it could allows derivatives to only specify their storage semantics. So your code would look like:
public abstract class ObjectModelBase<BllClass, EntityClass>
{
// ... same basic code here...
// supplied by your derivatives...
protected abstract Func<IQueryable<EntityClass>> GetEntitySet { get; };
protected abstract Func<Guid,Func<EntityClass,bool>> KeySelector { get; }
public BllClass GetById(Guid id)
{
using (db = new DataStoreEntities1())
{
EntityClass result = (EntityClass)((object)
GetEntitySet()
.Where( KeySelector( id ) )
.First();
return MapEntityToBLL(result);
}
}
}
public class OM_Customer : ObjectModelBase<ICustomer,Entity.Customer>
{
protected abstract Func<IQueryable<Entity.Customer>> GetEntitySet
{
get { return db.CustomerSet; }
}
protected abstract Func<Guid,Func<Entity.Customer,bool>> KeySelector
{
get { return (g => (e => e.Id == g)); }
}
}
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