Adding constraints

In the same way, you can add a notnull and an unique constraint on the lastname attribute within the class Person:

1. add the constraint specification to the class Person within the person.odl file as follows:

   class Person {
     string firstname;
     string lastname;
     int age;
     Address addr;
     ...
   
     index on firstname;
     index on lastname;
     index on age;
     constraint<notnull> on lastname;
     constraint<unique> on lastname;
   };
   

2. then, use the eyedbodl tool to update the database schema:

   % eyedbodl -U bill -P thekid -d foo -u --package=person person.odl
   Updating 'person' schema in database foo...
   Creating [NULL] notnull_constraint 'constraint<notnull, propagate = on> on Person.lastname' on class 'Person'...
   Creating [NULL] unique_constraint 'constraint<unique, propagate = on> on Person.lastname' on class 'Person'...
   
   Done
   

Now try to create two person instances with the same lastname attribute:

% eyedboql -U bill -P {bill password, i.e. 'thekid'} -d foo -w
? Person(lastname : "curtis");
= 6792.2.881020:oid
? Person(lastname : "curtis");
near line 3: 'Person()' => oql error: new operator <<new<oql\$db> Person()>> : notnull[] constraint error: attribute path 'Person.lastname'.

or with no lastname attribute:

? Person();
near line 3: 'Person()' => oql error: new operator <<new<oql\$db> Person()>> : notnull[] constraint error: attribute path 'Person.lastname'.