Question

Quite often in my LINQ to SQL code, I need to ‘find or create’ an entity as such:

var invoiceDb = ctx.Invoices.FirstOrDefault(a => a.InvoicerId == InvoicerId &&                                                  a.Number == invoiceNumber); if (invoiceDb == null) {     invoiceDb = new Invoice();     invoiceDb.Number = invoiceNumber;     ctx.Invoices.InsertOnSubmit(invoiceDb); } 

I’m looking to make this a generic method… Any good ideas?

Answer 1

I came up with these extension methods that seems to work well for me.

    public static T FindOrCreate<T>(this Table<T> table, Func<T, bool> find, Action<T> create) where T : class, new()     {         T val = table.FirstOrDefault(find);         if (val == null)         {             val = new T();             create(val);             table.InsertOnSubmit(val);         }         return val;     }      public static T FindOrCreate<T>(this Table<T> table, Func<T, bool> find) where T : class, new()     {         return FindOrCreate(table, find, a => { });     } 

And it’s used like so:

    var invoiceDb = ctx.Invoices.FindOrCreate(a => a.InvoicerId == InvoicerId &&                                                      a.Number == invoiceNumber);     invoiceDb.Number = invoiceNumber; 

Or

    var invoiceDb = ctx.Invoices.FindOrCreate(a => a.InvoicerId == InvoicerId &&                                                      a.Number == invoiceNumber,                                               a => a.Number = invoiceNumber);