Database Context save if valid

Question

I have question regarding Entity Framework. In my program I first fill-up my DbContext with data. Then I need to delete all the data from the tables in DB, but only if new data will be saved. If db.Savechanges() throws an exception I need my old data to still be in the tables.

My code is:

static void Main(string[] args)
        {
            PdmContext db = new PdmContext();

            FillDbContext();

            try
            {

                if (db.SaveChanges() > 0)
                {
                    using (var del = new PdmContext())
                    {
                        DeleteModel.deleteFromAllTables();
                    }
                    db.SaveChanges();
                }
            }
            catch (Exception exp)
            {
                Logger.Log("Exception (global catch));
            }
        }

I can't seem to figure this out. Anyone can help with this? :)

What does DeleteModel.deleteFromAllTables() do? And why do you need two instances of PdmContext? If you're deleting your data in a separate transaction and committing that transaction then that would certainly explain why that transaction is being committed. EF won't commit a transaction if an exception is thrown, so it seems that you're committing your deletes yourself somewhere. — David
– David, Commented Dec 13, 2018 at 12:56

Ehsan Sajjad · Accepted Answer · 2018-12-13 13:24:54Z

2

You can use Transaction which will make sure to revert the operation done within the scope of it if the operation fails at some stage :

using (var scope = new TransactionScope(TransactionScopeOption.Required))
{
      using (var del = new PdmContext())
      {
          DeleteModel.deleteFromAllTables();
      }
      db.SaveChanges();

      scope.Complete();  // commits the transaction     
}

Now the changes to the database will be atomic so that it will only keep all changes or not at all. I have not included exception handling code for simplicity but due to any reason if the scope.Complete() was not being executed and control exists the transaction block without executing that the transaction will get rolled back.

edited Dec 13, 2018 at 13:24

answered Dec 13, 2018 at 13:01

Ehsan Sajjad

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1 Comment

xcelm Over a year ago

Works like a charm! Thanks a lot! :)

Paulo · Accepted Answer · 2018-12-13 12:58:33Z

0

You need to use a Transaction.

see how to use that:

    using (var dbContextTransaction = PdmContext.Database.BeginTransaction())
            {
                try
                {
                   // HERE your operation insert etc.

                    PdmContext.SaveChanges();

                    dbContextTransaction.Commit(); // here, apply your operation
                }
                catch (Exception)
                {
                    dbContextTransaction.Rollback(); // here, undo your operations
                }
            }

answered Dec 13, 2018 at 12:58

Paulo

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Comments

AGH · Accepted Answer · 2018-12-13 13:17:16Z

You can handle such scenario with transaction management.

There is two way to handle it.

1) You can use single dbcontext for all operation instead of create multiple for single operation.

using (var context = new SchoolContext())
{

    try
    {


        context.Students.Add(new Student()
        {
            FirstName = "Rama2",
            StandardId = standard.StandardId
        });


        context.Courses.Add(new Course() { CourseName = "Computer Science" });
        context.SaveChanges();

        transaction.Commit();
    }
    catch (Exception ex)
    {
        transaction.Rollback();
        Console.WriteLine("Error occurred.");
    }
}

2) Using single DbContextTransaction object:

using (var context = new SchoolContext())
{
context.Database.Log = Console.Write;

using (DbContextTransaction transaction = context.Database.BeginTransaction())
{
    try
    {
          context.Students.Add(new Student()
        {
            FirstName = "Rama2",
            StandardId = standard.StandardId
        });


        context.SaveChanges();

        context.Courses.Add(new Course() { CourseName = "Computer Science" });
        context.SaveChanges();

        transaction.Commit();
    }
    catch (Exception ex)
    {
        transaction.Rollback();
        Console.WriteLine("Error occurred.");
    }
}
}

I hope it work for you.

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