How to insert identity value in Oracle using Entity Framework using a sequence

Question

In an Oracle database, that has an ID column defined as a number:

...and a corresponding sequence for the table...:

How do I make sure the ID column gets the next value in the sequence?

using (var db = new MyOracleDb()){
    var user= new User(){ first_name = 'Abe', last_name = 'Lincoln'};
    //Do something here with the sequence and set the ID?
    db.User.Add(user);
    db.SaveChanges();
}

I am using the latest Oracle.ManagedDataAccess and Oracle.ManagedDataAccess.EntityFramework + EF6x.

Answer 1

This is not an EF issue, as there is no auto increment in oracle. You will have to either get the sequence value manually, or create a trigger to set it for you.

Update

In order to get the sequence value you have two options - either create a stored procedure, that returns the value - or create a .Net function ( doesn't really have to be in a function, it's just simpler) that calls raw SQL like this:

Database.SqlQuery<int>("SELECT SEQ_SOMESEQ.NEXTVAL FROM dual");

I personally had many issues with oracle functions and EF, so I would go with the raw sql.

Answer 2

I've created an interface:

public interface IHasSequencer
{
    decimal Id { get; set; }
    string GetSequenser();
}

Then implemented it in my model:

[Table("CLN_CLIENTS")]
public class ClnClient : IHasSequencer
{
    public string GetSequenser()
    {
        return "SEQ_CLN_CLIENTS";
    }

    [Key, Column("ID")]
    public decimal Id { get; set; }

    [Column("FIRSTNAME")]
    public string FirstName { get; set; }

    [Column("LASTNAME")]
    public string LastName { get; set; }

    [Column("MIDDLENAME")]
    public string MiidleName { get; set; }
}

And added some MAGIC overriding SaveChanges() method in my DbContext:

 public override int SaveChanges()
    {
        var addedEntries = ChangeTracker.Entries().Where(e => e.State == EntityState.Added);

        foreach (DbEntityEntry entry in addedEntries)
        {
            if (entry.Entity is IHasSequencer)
            {
                var sequencerEntity = entry.Entity as IHasSequencer;
                var nextSeqVal = Database.SqlQuery<Int64>("SELECT " + sequencerEntity.GetSequenser() + ".NEXTVAL FROM DUAL").First();
                sequencerEntity.Id = nextSeqVal;
            }
        }
        return base.SaveChanges();
    }

That's it! Now models that need sequenceer ID value must implement small interface.

Answer 3

Just FYI, With Entity Framework I had issues with unique constraints. For future readers if you're still having unique constraint issues. Please make sure you change the property "StoreGeneratedPattern" to your requirement.

For me I was adding MAX(ID) + 1 and had StoreGeneratedPattern set as Identity which started to work fine but after sometime break the whole program by throwing the same unique constraint issue, which when I checked database was definitely not the case. It was something that most developers didn't pay attention to.

I've changed it to "None" So I have control over it to what to add rather than entity framework breaking it after every few days. Entity Framework Property Picture

Answer 4

If you create the trigger on Oracle's side you don't have to worry about it on your code. It works as if it did have an Identity.