Concatenating ids with extension to keep multiple rows related to an entity in a single Column Family

Question

I am concatenating two Integer ids through bitwise operations(as described below) to create a single primary key of type long. I wanted to know if this is a good practice. This would help me in keeping multiple rows of an entity in a single column family by appending different extensions to the entityId. Are there better ways ? My Ids are of type Integer(4 bytes).

public static final long makeCompositeKey(int entityId, int extension){
    return (long)entityId << 32 | extension;
}

Answer 1

Most databases come with a built-in way to create IDs automatically, and your app doesn't need to care about it. I'm most familiar with Postgres, where I create a sequence for each table and use that for the @Id column, but I know that Oracle and MSSQL have their own way of accomplishing the same thing.

In general, however, each column in your database should store a single piece of information. Taking two pieces of info and concatenating them together as you're suggesting goes against "proper" database design according to "book learning." By which I mean: you should only do it if you have a very, very good reason for doing so (and even then, you should think two or three times about it before actually doing it.) If you don't have a good reason for doing it, then don't do it.

Answer 2

This is not a good design. It should be two different columns having composite constraint. You can have a another generated Unique ID for as a primary key.

Aside from the primary key, You can also create a composite index on two columns to speed up the queries if most queries will filter based on these two values.