How to use ObjectContext with Model Builder? - entity-framework-5

Question

Is there a way we can use ObjectContext with DbContext's ModelBuilder? We don't want to use POCO because we have customized property code that does not modify entire object in update, but only update modified properties. Also we have lots of serialisation and auditing code that uses EntityObject.
Since poco does create a proxy with EntityObject, we want our classes to be derived from EntityObject. We don't want proxy. We also heavily use CreateSourceQuery. The only problem is EDMX file and its big connection string syntax web.config.
Is there any way I can get rid of EDMX file? It will be useful as we can dynamically compile new class based on reverse engineering database.
I would also like to use DbContext with EntityObject instead of poco.
Internal Logic
Access Modified Properties in Save Changes which is available in ObjectStateEntry and Save them onto Audit with Old and New Values
Most of times we need to only check for Any condition on Navigation Property for example
User.EmailAddresses.CreateSourceQuery()
.Any( x=> x.EmailAddress == givenAddress);
Access Property Attributes, such as XmlIgnore etc, we rely heavily on attributes defined on the properties.

Answer 1

A proxy for a POCO is a dynamically created class which derives from (inherits) a POCO. It adds functionality previously found in EntityObject, namely lazy loading and change tracking, as long as a POCO meets requirements. A POCO or its proxy does not contain an EntityObject as the question suggests, but rather a proxy contains functionality of EntityObject. You cannot (AFAIK) use ModelBuilder with EntityObject derivatives and you cannot get to an underlying EntityObject from a POCO or a proxy, since there isn't one as such.
I don't know what features of ObjectContext does your existing serialisation and auditing code use, but you can get to ObjectContext from a DbContext by casting a DbContext to a IObjectContextAdapter and accessing IObjectContextAdapter.ObjectContext property.
EDIT:
1. Access Modified Properties in Save Changes which is available in ObjectStateEntry and Save them onto Audit with Old and New Values
You can achieve this with POCOs by using DbContext.ChangeTracker. First you call DbContext.ChangeTracker.DetectChanges to detect the changes (if you use proxies this is not needed, but can't hurt) and then you use DbCotnext.Entries.Where(e => e.State != EntityState.Unchanged && e.State != EntityState.Detached) to get DbEntityEntry list of changed entities for auditing. Each DbEntityEntry has OriginalValues and CurrentValues and the actual Entity is in property Entity.
You also have access to ObjectStateEntry, see below.
2. Most of times we need to only check for Any condition on Navigation Property for example:
User.EmailAddresses.CreateSourceQuery().Any( x=> x.EmailAddress == givenAddress);
You can use CreateSourceQuery() with DbContext by utilizing IObjectContextAdapter as described previously. When you have ObjectContext you can get to the source query for a related end like this:
public static class DbContextUtils
{
public static ObjectQuery<TMember> CreateSourceQuery<TEntity, TMember>(this IObjectContextAdapter adapter, TEntity entity, Expression<Func<TEntity, ICollection<TMember>>> memberSelector) where TMember : class
{
var objectStateManager = adapter.ObjectContext.ObjectStateManager;
var objectStateEntry = objectStateManager.GetObjectStateEntry(entity);
var relationshipManager = objectStateManager.GetRelationshipManager(entity);
var entityType = (EntityType)objectStateEntry.EntitySet.ElementType;
var navigationProperty = entityType.NavigationProperties[(memberSelector.Body as MemberExpression).Member.Name];
var relatedEnd = relationshipManager.GetRelatedEnd(navigationProperty.RelationshipType.FullName, navigationProperty.ToEndMember.Name);
return ((EntityCollection<TMember>)relatedEnd).CreateSourceQuery();
}
}
This method uses no dynamic code and is strongly typed since it uses expressions. You use it like this:
myDbContext.CreateSourceQuery(invoice, i => i.details);