Dapper Tutorial Dapper Contrib - Data Annotation - ExplicitKey


The Key attribute assumes an autoincremented key, and when you try to pass a custom key instead, it will fail with NullReferenceException, even if the passed value isn't null.

  • The solve this problem ExplicitKey was introduced to handle those instead.
  • It Specifies the property as a key that is NOT automatically generated by the database.
  • The ExplicitKey attribute is used to identify multiple columns as the primary key.
  • It is useful when you have a composite primary key (a primary key that consists of more than one column).

In the following example, the InvoiceID property of the InvoiceDetailContrib class is decorated with an ExplicitKey attribute to specify the primary key of a table.

public class InvoiceDetailContrib
	public int InvoiceID { get; set; }

	public string Detail { get; set; }

using (var connection = My.ConnectionFactory())

	var invoice = new InvoiceContrib {Kind = InvoiceKind.WebInvoice, Code = "Insert_Single_1"};

	var invoiceDetail = new InvoiceDetailContrib {InvoiceID = invoice.InvoiceID, Detail = "Insert_Single_1"};

The InvoiceID property of the InvoiceDetailContrib class must be assigned a value because it will not be generated automatically by the database.