Is getOrCreate function a good or a bad practice?

That depends on many factors. For example you might keep a local cache for some tables. Now, if you call getOrCreate(someValue) on that table, then You will have to know whether you created it or just retrieved it . Because you might need to flush and reload the cache (by making another read operation).

You might have other dependencies which might cause significant problems later on.

Though I don't completely say that this is a bad practice, I think its better to seperate your concerns.

You could do something like -

if(searchForRecord()==null)
 {
  addRecord();
 }

Advantage of this approach : You will always know the state and behaviour of your system (what is happening).

Singleton pattern is a totally different thing. You always get ONLY ONE OBJECT. And creation of that object is handled internally and is private to the Singleton class. You DONT need to know whether you get a new object or the old one because it doesn't matter to you.

It's a get function. You get an instance of the class.

It doesn't matter to the outside world how the get function works internally.

    public Object getObject(int key) {
        Object object = getObjectFromDatabase(key);
        if (object == null) {
            object = createObject(key);
            writeObjectToDataBase(key, object);
        }
        return object;
    }

Every method has one function.

Edited to add: Some people look at methods from the inside out. That's what you need to do when you're writing the code for the method. I recognized that my getObject method had to do several things to truly get an Object.

However, when you're naming the method, you look at a method from the outside. Which is why my getObject method "gets an Object" (pretty short Javadoc description). If you can't write a simple declarative sentence describing the function of your method, your method is possibly too complicated.