如何通过传入对象使用实体框架进行更新

Question

How do I update using Entity Framework? I'm passing in the object with the updated values, but I don't see an Update method.

   public void UpdateRecipient(Domain.Entities.RecipientEntity recipient)
    {
        using (EfDbContext context = CreateEfDbContext(recipient.ApplicationId.ToString()))
        {

            context.Recipients. //?? I don't see an update method
            context.SaveChanges();

        }
    }

Answer 1

Three steps:

1. Get the item to update from the context
2. Copy over the updated properties from the entity you pass your update method
3. Save the changes.

Roughly:

using (EfDbContext context = CreateEfDbContext(recipient.ApplicationId.ToString()))
{
    var toUpdate = context.Recipients.SingleOrDefault(r => r.Id == recipient.Id);
    if (toUpdate != null)
    {
        toUpdate.Field1 = recipient.Field1;
        // Map over any other field data here.

        context.SaveChanges();
    }
    else
    {
        // Handle this case however you see fit.  Log an error, throw an error, etc...
    }
}

Answer 2

There is another way of updating object without re-fetching it from the database again thus by saving cost of a trip to database. The object being attached must have a value for its primary key.

1. Attach the updated object to the context
2. Change it's state to 'modified'.
3. Call SaveChanges() method of the context

Like:

 public void UpdateRecipient(Domain.Entities.RecipientEntity recipient)
    {
        using (EfDbContext context = CreateEfDbContext(recipient.ApplicationId.ToString()))
        {
            context.Attach(recipient);
            context.ObjectStateManager.ChangeObjectState(recipient,EntityState.Modified);
            context.SaveChanges();    
        }
    }

Answer 3

If you're updating the record then you'd do something like this:

//Retrieve the entity to be updated
Entity row = context.Recipients.Single(a => a.Id == recipient.Id);

//Update a column
row.Name = recipient.Name;

//Save changes
context.SaveChanges();

If you want to update/add things at the same time then you'd do:

if(!context.Recipients.Any(a => Id == recipient.Id))
{
    context.Recipients.Add(recipient);
}
else
{
    Entity row = context.Recipients.Single(a => a.Id == recipient.Id);

    row.Name = recipient.Name;
}

context.SaveChanges();