Save Changes to EntityObject using Multiple Instances of One Context

Question

My Problem is the following. I have a DataAccessLayer Project with a DalClass. In this Dal class I have many Methods for operations with Entity Framework. For example some pseudo-code to show how we do it.

class DalClass
{    
    public void SetEntityObject(EntityObject entityObject)
    {
        using (var context = new Entities())
        {
            context.EntityObjectSet.Attach(entityObject);
            context.ChangeTracker.DetectChanges();
            foreach (var entity in context.ChangeTracker.Entries())
            {
                entity.State = entityObject.EntityState;
            }

            context.SaveChanges();
        }
    }

    public EntityObject GetEntitObject(Guid id)
    {
        EntityObject result;
        using (var context = new Entities())
        {
            result = context.EntityObjectSet.Where(x => x.Id == Id);  
        }

        return result;
    }
}

Each time we do operations with EF we create a new instance context and do some work. My problem is that I have a method in my DalClass to get a List of EntityObjects Like this :

    public List<EntityObject> GetEntityObjectsByIds(List<Guid> idList)
    {
        using (var context = new Entities())
        {
            var query = from entityObject in context.EntityObjectSet
                        where idList.Contains(entityObject.Id)
                        select entityObject;

            return query.ToList();
        }
    }

After I return the List to my Business Layer class. I do some changes to each EntityObject, calculations, change some Property values and so on. After that I call a method from my BusinessLayer class to save the new edited List with this method:

    public void UpdateEntityObjects(List<EntityObject> newEntityObjectList)
    {
        using (var context = new Entities())
        {
            var idList = entityObjectList.Select(x => x.Id).ToList();

            var query = from entityObject in context.EntityObjectSet
                        where idList.Contains(entityObject.Id)
                        select entityObject;

            var entityObjectList = query.ToList();
            entityObjectList = newEntityObjectList;

            context.ChangeTracker.DetectChanges();
            foreach (var entity in context.ChangeTracker.Entries())
            {
                entity.State = EntityState.Modified;
            }
            context.SaveChanges();
        }
    }

Problem I can not save newEntityObjectList that I Edited in my BusinessLayer. Obviously this is not working.

entityObjectList = newEntityObjectList;

So how is the best way to save the newEntityObjectList ?

Problem I have to fier this query twice

            var query = from entityObject in context.EntityObjectSet
                    where idList.Contains(entityObject.Id)
                    select entityObject;

Solution to 2. Problem could be if I use one Context instance for GetEntityObjectsByIds() and UpdateEntityObjects(). But in all our Dal Classes we avoided that. Even if I use one instance of Context class, this does not solve Problem 1. So how can I save newEntityObjectList ?

Milos Mijatovic · Accepted Answer · 2014-12-08 23:17:10Z

1

Well, my DAL class would most definetely be something like this:

class EntityObjectDAL 
{
    private ObjectContext/DbContext context = new ObjectContext/DbContext();

    public List<EntityObject> GetObjects() { return context.EntityObjects.ToList(); }
    // Tracked by context. Just change it in BL

    public void SaveObjects() { context.SaveChanges(); }
    // Just call SaveChanges(), no need for anything special...

    public void InsertObject(EntityObject eo) { context.EntityObjects.Add(eo); }

    public void UpdateObject(EntityObject eo) { context.Entry(eo).State = EntityState.Modified; }
}

Keep it simple...

answered Dec 8, 2014 at 23:17

Milos Mijatovic

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5 Comments

xargs Over a year ago

Thanks for Respond Milos. As I said in the Quastion if I use one instance of Context it would work, but i would like to avoid that approach. Is there a way to do this with 2 Instances of Context for this example ?

Milos Mijatovic Over a year ago

Well, what are newEntityObjectList? Are those new entities or are those loaded from another context? If those are new, how do you create them: context.EntityObjects.Create() or just new EntityObject()? I suppose you always need to detach them from previous context (hence just more work in case of 2 contexts), and then attach them to new one by calling Add() or Attach() methods. And change entityState, ofcourse. That's how I would try, anyway.

xargs Over a year ago

newEntityObjectList is the List of Objects that I get from the first method with first method List<EntityObject> GetEntityObjectsByIds(List<Guid> idList) that uses 1 Context, the name now is just newEntityObjectList because I have done some Editing on the Objects and their Porperties

Milos Mijatovic Over a year ago

well, normally, you would need to detach entities from context, but your first context is destroyed, so i think that's not necessary. Did you try just iterating over entities in the list, attaching it to a new context via context.EntityObjectSet.Attach() and changing entity state to modified like you already do. And then just call SaveChanges()? If yes, what error do you get?

xargs Over a year ago

Sorry for late answer Milos. I solved the Problem with using just one Context. I made my changes to my EntityObjectList and Saved it. With 2 Instances of Context it would be much Work but I dont see the benefits right now. Thanks for answer :)

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