Cloning data on Entity Framework

Question

I am creating software where user can create new product based on older product.

Now I need to make copying / cloning operations with Entity Framework. First I started writing like this:

foreach(sourcedata1 in table1)
{
   ... create new table
   ... copy data
   ... create Guid
   ... add
   foreach(sourcedata2 in table2)
   {
       ... create new table
       ... copy data
       ... create Guid
       ... add       

       ... and so on
   }
}

Problem is that this not a nice way to do it. Is there any easy way clone information (except Guid that needs to be generated for new rows) or should I manually copy everything?

Other solution

You could also use EmitMapper or AutoMapper to do copying of the properties.

Answer 1

To clone an Entity in Entity Framework you could simply Detach the entity from the DataContext and then re-add it to the EntityCollection.

context.Detach(entity);
entityCollection.Add(entity);

---

Update for EF6+ (from comments)

context.Entry(entity).State = EntityState.Detached;
entity.id = 0;
entity.property = value;
context.Entry(entity).State = EntityState.Added;
context.SaveChanges();

Answer 2

public static EntityObject Clone(this EntityObject Entity)
{
    var Type = Entity.GetType();
    var Clone = Activator.CreateInstance(Type);

    foreach (var Property in Type.GetProperties(BindingFlags.GetProperty | BindingFlags.Public | BindingFlags.Instance | BindingFlags.DeclaredOnly | BindingFlags.SetProperty))
    {
        if (Property.PropertyType.IsGenericType && Property.PropertyType.GetGenericTypeDefinition() == typeof(EntityReference<>)) continue;
        if (Property.PropertyType.IsGenericType && Property.PropertyType.GetGenericTypeDefinition() == typeof(EntityCollection<>)) continue;
        if (Property.PropertyType.IsSubclassOf(typeof(EntityObject)))  continue;

        if (Property.CanWrite)
        {
            Property.SetValue(Clone, Property.GetValue(Entity, null), null);
        }
    }

    return (EntityObject)Clone;
}

This is a simple method I wrote. It should work for most people.

Answer 3

To add a new row whose content is based on an existing row, follow these steps:

1. Get an entity based on the starting row.
2. Set the entry state for the entity to Added.
3. Modify the entity.
4. Save changes.

Here's an example:

var rabbit = db.Rabbits.First(r => r.Name == "Hopper");
db.Entry(rabbit).State = EntityState.Added;
rabbit.IsFlop = false;
db.SaveChanges();

Answer 4

If you want to create a copy of an entity for comparison later in your code execution, you can select the entity in a new db context.

If for example you are updating an entity, then later in the code you want to compare the updated and original entity:

var db = new dbEntityContext();
var dbOrig = new dbEntityContext();

var myEntity = db.tblData.FirstOrDefault(t => t.Id == 123);
var myEntityOrig = dbOrig.tblData.FirstOrDefault(t => t.Id == 123);

//Update the entity with changes
myEntity.FirstName = "Gary";

//Save Changes
db.SaveChnages();

At this point, myEntity.FirstName will contain "Gary" whilst myEntityOrig.FirstName will contain the original value. Useful if you have a function to log changes where you can pass in the updated and original entity.

Answer 5

A really short way of duplicating entities using generics (VB, sorry).
It copies foreign key values (external IDs) but doesn't load their related objects.

<Extension> _
Public Function DuplicateEntity(Of T As {New, Class})(ctx As myContext, ent As T) As T
    Dim other As New T 'T is a proxy type, but New T creates a non proxy instance
    ctx.Entry(other).State = EntityState.Added 'attaches it to ctx
    ctx.Entry(other).CurrentValues.SetValues(ent) 'copies primitive properties
    Return other
End Function

For instance:

newDad = ctx.DuplicateEntity(oDad)
newDad.RIDGrandpa ' int value copied
newDad.Grandpa    ' object for RIDGrandpa above, equals Nothing(null)
newDad.Children   ' nothing, empty

I don't know exactly how to reload Grandpa in this case.
This doesn't work:

ctx.SaveChanges()
ctx.Entry(newDad).Reload()

but really, no problem. I would rather assign Grandpa by hand if I need it.

newDad.Grandpa = oDad.Grandpa

EDIT: As MattW proposes in his comment, detaching and finding the new entity you get its children loaded (not collections).

ctx.Entry(newDad).State = EntityState.Detached
ctx.Find(newDad.RowId) 'you have to know the key name