Layer Supertype

A type that acts as the supertype for all types in its layer

Often all the objects in a layer will have some common methods that you don't want to have duplicated throughout the system. So you can move all of this behavior into a common Layer Supertype.

How it Works

Layer Supertype is a simple idea that leads to a very short pattern. All you need is a superclass for all the objects in a layer. For example all the domain objects in a Domain Model might have a superclass called Domain Object. Common features, such as the storage and handling of Identity Fields can go there. Similarly all Data Mappers in the mapping layer may have a superclass which can rely on the fact that all the domain objects have a common superclass.

If you have more than one kind of object in a layer, then it's useful to have more than one Layer Supertype.

When to Use it

Use Layer Supertype when you have common features from all objects in a layer. Often I do this automatically now, because I so often make use of common features.

Example: Domain Object (Java)

Domain objects can have a common superclass for id handling.

class DomainObject... 
	private Long ID;

	public Long getID() {
		return ID;
	}

	public void setID(Long ID) {
		Assert.notNull("Cannot set a null ID", ID);
		this.ID = ID;
	}

	public DomainObject(Long ID) {
		this.ID = ID;
	}

	public DomainObject() {
	}