Question

I have an application running that has entities that might be: CustomerType1, CustomerType2, and CustomerType3.

All three CustomerType entities might have completely different information, but they all have a CustomerID field which is an integer.

I am trying to figure out how to set things up so that no matter which type is created, the CustomerID will always be unique across all three types, and remain an integer.

For example, creating the following would result in the following CustomerID

CustomerType1 – 1

CustomerType1 – 2

CustomerType1 – 3

CustomerType2 – 4

CustomerType1 – 5

CustomerType3 – 6

CustomerType1 – 7

What is the best way to approach this?

Answer 1

2 possible approaches:

1. Use a single table for all of your customer types with a “discriminator” field to track each customer type, and include the CustomerID as its identity.
2. Use an external table to manage creating the CustomerID as an identity field.

The first approach has the advantage of having direct support in the Entity Framework for as outlined in the following tutorial:

http://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/implementing-inheritance-with-the-entity-framework-in-an-asp-net-mvc-application

Note that although your customer types may contain different data, this approach could end up being cheaper in the long run in terms of scalability despite the wasted database space. In your business layer, the customer types could simply ignore the fields that don’t pertain to them.

The second approach would probably be best suited to adding onto existing applications that are too difficult to change. In the long run, there is more work involved with keeping track of the IDs this way. For one, your business layer will need to fetch an ID from one table in order to insert into another table, which can be expensive for large datasets. Depending on the requirements of the business layer, there may also be scenarios where you have to discard an unused CustomerID and it would simply not exist in the system (you would skip from CustomerID 58 to CustomerID 60 for example).