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Identity

The Identity<> value object provides generic functionality to create and validate the IDs of aggregate roots. It is basically a wrapper around a Guid.

Let's say we want to create a new identity named TestId. We could do it like this:

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public class TestId : Identity<TestId>
{
  public TestId(string value)
    : base(value)
  {
  }
}
  • The identity follows the form {classname without "Id"}-{guid} e.g. test-c93fdb8c-5c9a-4134-bbcd-87c0644ca34f for the above TestId example.

  • The internal Guid can be generated using one of the following methods/properties. Note that you can access the Guid factories directly by accessing the static methods on the GuidFactories class:

    • New: Uses the standard Guid.NewGuid().
    • NewDeterministic(...): Creates a name-based Guid using the algorithm from RFC 4122 ยง4.3, which allows identities to be generated based on known data, (e.g., a user e-mail). It always returns the same identity for the same arguments.
    • NewComb(): Creates a sequential Guid that can be used to avoid database fragmentation.

  • A string can be tested to see if it's a valid identity using the static bool IsValid(string) method.

  • Any validation errors can be gathered using the static IEnumerable<string> Validate(string) method.

Attention

It's very important to name the constructor argument value as it is significant when the identity type is deserialized.

Here are some examples of how we can use our newly created TestId:

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// Uses the default Guid.NewGuid()
var testId = TestId.New;

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// Create a namespace, put this in a constant somewhere
var emailNamespace = Guid.Parse("769077C6-F84D-46E3-AD2E-828A576AAAF3");

// Creates an identity with the value "test-9181a444-af25-567e-a866-c263b6f6119a"
var testId = TestId.NewDeterministic(emailNamespace, "test@example.com");

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// Creates a new identity every time, but an identity when used in
// database indexes, minimizes fragmentation
var testId = TestId.NewComb();

Tip

Be sure to read the section about value objects as the Identity<> is basically a value object.