SQL : Generic access to schema metadata in Q-types

[Timo Westkämper]

Table metadata like columns, primary keys, foreign keys, column constraints (size, nullability) should be provided in generic form in Q-types. On many jdbc drivers this information can be read from the metadata. This information can be used to automate some tasks with UI development.

[Timo Westkämper (timo-westkamper)]

Something like this maybe

interface RelationalEntity {

  PrimaryKey getPrimaryKey();

  Set<ForeignKey> getForeignKeys();

  Set<ForeignKey> getInverseForeignKeys();

}

In my opinion the column constraints could be bound to the properties as Bean Validation annotatios : http://people.redhat.com/~ebernard/validation/

This approach would also work with the Bean generation approach. For the BeanGeneration approach the annotations would be in the Bean :

class QProduct extends PEntity<Product> implements RelationalEntity{
  PNumber<Long> id;
  PString name;
}

@Table("PRODUCT")
class Product {

  @NotNull
  @Column("ID")
  Long id;

  @Size(max=256)
  @Column("NAME")
  String name;
}

or alternatively without the bean generation

@Table("PRODUCT")
class QProduct extends PEntity<Product> implements RelationalEntity{
  @NotNull
  PNumber<Long> id;

  @Size(max=256)
  PString name;
}

RelationalEntity could also be a subclass of PEntity :

public abstract class RelationEntity<E> extends PEntity<E> {

  public abstract PrimaryKey getPrimaryKey();

  public abstract Set<ForeignKey> getForeignKeys();

  public abstract Set<ForeignKey> getInverseForeignKeys();

}

What do you think?

[Timo Westkämper (timo-westkamper)]

Related forum thread : http://source.mysema.com/forum/mvnforum/viewthread_thread,103

[Timo Westkämper (timo-westkamper)]

Added RelationalPath interface to Querydsl SQL generated Q-types :

public interface RelationalPath<T> extends EntityPath<T>{

    PrimaryKey<T> getPrimaryKey();

    Collection<ForeignKey<?>> getForeignKeys();

    Collection<ForeignKey<?>> getInverseForeignKeys();

}

The constraints part of schema metadata access will be continued in the Bean class code generation issue : https://bugs.launchpad.net/querydsl/+bug/604727

[Timo Westkämper (timo-westkamper)]

Released in 1.9.0