Where can I find a C# implementation of the "Identity Field" (fowler) pattern that support multiple fields of different types

Question

I've found one that allows multiple fields of type long. However, i'm not sure how useful that is since sometimes we may have Guids or even dates for example.

I could also modify his to support my needs, but this seems like it would be such a common request that I should be able to find something tested, tried and true instead of creating it from scratch.

The main purpose i have behind this is use the Identity Map pattern. I believe this pattern more or less requires the Identity Field pattern to support it. I will use the Identity Field construct as the key to my dictionary

Any ideas?

Thanks

Answer 1

I think to implement a similar pattern for a multi-column PK, you would just need to create a field/property on your class for each of the PK columns on the table.

For example, if you had a "Message" table with a PK with a long, a guid, and a datetime, your class would just need to include a long, Guid, and a DateTime property.

You would probably also want to implement Equals() and GetHashCode() for the object using these PK fields, because you want these objects to compare in database terms, not in terms of the in-memory address of the object. GetHashCode is important, because you want to ensure that Objects with the same PK properties produce the same hash code. To implement GetHashCode, I would recommend looking at Jon Skeet's answer here: What is the best algorithm for an overridden System.Object.GetHashCode?

Fowler's "Identity Field" pattern maybe assuming that your tables have a single surrogate PK column, and that is why he specifies it the way he does.

Answer 2

Check out S#arp Architecture. When you inherit from their Entity object, you can decorate as many properties as you want to with the DomainSignatureAttribute. These properties will then be considered as the object's identity in the implementation of Equals and GetHashCode that is provided in Entity.