What is the best practice when implementing equals() for entities with generated ids

If I have a table with columns A, B, C, D  A: auto-generated id (PK)  B & C: combination must be unique (these are the columns that actually define identity in the business sense)  D: some other columns

Now, if I'll create business objects based on this table (e.g. in Java), which one would be a better implementation of the equals() method:

  1. define equality based on A
  2. define equality based on B and C

or, it wouldn't really matter which of the two I choose.


Definitely B and C, because you want the equals() contract to be valid even before entities are persisted. You say yourself:

these are the columns that actually define identity in the business sense

If that is the case, then that is the logic equals() should use. Database keys are the database's concern and should be of no concern to your business layer.

And don't forget to use the same properties in hashcode(), too.

Need Your Help

j2me service discovery and discoverable same time

java java-me mobile client-server bluetooth

I try to write a simple client/server application (all application is a bluetooth service and client). The client code find the bluetooth devices and register in to the local db. But when the inquiry

Reading format in Fortran 90

format fortran

I have a huge file to read whose structure is:

About UNIX Resources Network

Original, collect and organize Developers related documents, information and materials, contains jQuery, Html, CSS, MySQL, .NET, ASP.NET, SQL, objective-c, iPhone, Ruby on Rails, C, SQL Server, Ruby, Arrays, Regex, ASP.NET MVC, WPF, XML, Ajax, DataBase, and so on.