How to enable database diagram on SQL Server 2008

You have to enable database diagram on SQL Server, otherwise when you try to create a database diagram on SQL Server 2008, you are greeted with this message:

TITLE: Microsoft SQL Server Management Studio
——————————

Database diagram support objects cannot be installed because this database does not have a valid owner.  To continue, first use the Files page of the Database Properties dialog box or the ALTER AUTHORIZATION statement to set the database owner to a valid login, then add the database diagram support objects.

——————————
BUTTONS:

OK
——————————
So, first go to the database properties and select the Files tab. Select a valid login as the DB owner. Then go back to the Database Diagrams folder, right click and select Install Diagram Support. The next dialog show this message:

TITLE: Microsoft SQL Server Management Studio
——————————

This database does not have one or more of the support objects required to use database diagramming.  Do you wish to create them?

——————————
BUTTONS:

&Yes
&No
——————————
Click Yes.

Now go back and create a diagram.