Question

in MVC 3 is it possible to rollback the database after calling DbContext.SaveChanges() ?

My entities class:

public class BipEntities : DbContext
{
    public DbSet<Page> Pages { get; set; }
    public DbSet<ImageFile> ImageFiles { get; set; }
}

What I’m trying to do is insert a ImageFile record into the db, then by using the auto-incremented id as the image filename, save the image file into somewhere else.
When System.IO fails, I would like to rollback the database.

BipEntities db = new BipEntities();
db.Database.Connection.Open();
DbTransaction tranx = db.Database.Connection.BeginTransaction();

ImageFile img = new ImageFile { CreatedAt = DateTime.Now };
db.ImageFiles.Add(img);
db.SaveChanges();

string filename = "img" + img.Id.ToString() + ".png";
try {
    //Works on system IO to process file
    tranx.Commit();

} Catch ( Exception) {
    tranx.Rollback();
}

db.Database.Connection.Close();

However, the above code gives me this error message:

EntityConnection can only be constructed with a closed DbConnection.

Answer 1

You should wrap your DbContext in a database transaction, either using a TransactionScope or creating the DbContext using a DbConnection that runs inside a transaction:

using (var con = new SqlConnection(conStr))
{
    con.Open();
    using (var tran = con.BeginTransaction())
    {
        var img = new Image();

        using (var db = new BipEntities(con))
        {
            db.Images.AddObject(img);

            db.SaveChanges();
        }

        // Write to disk here.
        WriteStuffToDisk(stuff, img.Id);

        tran.Commit();
    }        
}