entity framework 6 - check if record exists before insert and concurrency

Question

I have the following scenario:

A business logic function that uses ef6 checks if a record already exists. If the record does not exists, it is inserted on the databa

Answer 1

I would harness the concurrency handling built into Entity Framework rather than write my own logic.

You add a concurrency token to the database. Typically this would be a RowVersion field:

Using FluentAPI:

modelBuilder.Entity() 
    .Property(t => t.Timestamp) 
    .IsRowVersion(); 

Using Data Annotations:

 [Timestamp]
 public byte[] RowVersion { get; set; }

Typically you then handle the DbUpdateConcurrencyException thrown when there is a problem:

        using (var context = new SchoolDBEntities())
        {
            try
            {
                context.Entry(student1WithUser2).State = EntityState.Modified;
                context.SaveChanges();
            }
            catch (DbUpdateConcurrencyException ex)
            {
                Console.WriteLine("Optimistic Concurrency exception occured");
            }
        }

References:

Configuring a concurrency token

Handling concurrency in Entity Framework

Optimistic concurrency patterns using Entity Framework

EDIT Just realised that I have misread your question. You aren't really talking about concurrency here, as your question title suggests. You just want to ensure that a record's natural key is unique. The way to do that is over here: https://stackoverflow.com/a/18736484/150342