C#, entity framework, auto increment

Question

I\'m learning Entity Framework under VC# 2010.

I have created a simple table for learning purposes, one of the fields is \"id\" type integer, identity set to true. I

Answer 1

I had similar issues, which occurred in EF6 (did work in EF4 without transactions, EF 4 used implicit transactions with the right scope).

Just creating a new entity and saving it did not help in my case (see the comments of the other answers, they had similar issues with using dc.SaveChanges() only to auto-update).

Consider the following code (CustomerId is the primary key with auto-increment):

public void UpdateCustomer(string strCustomerName, string strDescription)
{
  using (var transaction = CreateTransactionScope())
  {
    MyCustomer tbl=null;
    Func selectByName=(i => i.CustomerName.Equals(strCustomerName));
    var doesRecordExistAlready = dc.MyCustomers.Any(selectByName); 
    if (doesRecordExistAlready) 
    {
        // Updating
        tbl=dc.MyCustomers.Where(selectByName).FirstOrDefault();        
        tbl.Description=strDescription;
    }
    else
    {
        // Inserting
        tbl=new MyCustomer(); 
        var maxItem=
           dc.MyCustomers.OrderByDescending(i => i.CustomerId).FirstOrDefault();
        var newID = maxItem==null ? 1 : maxItem.CustomerId+1;
        tbl.CustomerId=newID;
        tbl.CustomerName=strCustomerName; 
        tbl.Description=strDescription;
        dc.MyCustomers.AddObject(tbl);      
    }
    dc.SaveChanges(); // save all changes consistently          
    transaction.Complete(); // commit
  }
}

And the helper function to create the right transaction context is:

// creates the right transaction scope
public static System.Transactions.TransactionScope CreateTransactionScope() 
    // needs to add ref: System.Transactions
 { 
    var transactionOptions = new TransactionOptions 
    { 
        IsolationLevel = System.Transactions.IsolationLevel.ReadUncommitted,
        Timeout = new TimeSpan(0,0,10,0,0) //assume 10 min is the timeout time
    }; 
    var scopeOption=TransactionScopeOption.RequiresNew;
    var scope = new System.Transactions.TransactionScope(scopeOption, 
               transactionOptions); 
    return scope;
} 

The trick is here, to allow reading uncommitted - hence you can query the max ID and add 1 to id. What I wasn't able to achieve is to let SQL server generate the ID automatically, because EF doesn't allow to omit the CustomerId upon creation.

To read more about transaction scope, look here.