Extend your IDbConnection with high-performance bulk operations
DapperPlusManager.Entity<Invoice>().Identity(x => x.InvoiceID, true);
DapperPlusManager.Entity<InvoiceItem>().Identity(x => x.InvoiceItemID, true);
// ...code...
connection.BulkInsert(invoices, x => x.InvoiceMeta, x => x.InvoiceItems);
Try it: https://dotnetfiddle.net/LBfItU