使用hibernate注释将枚举映射到表

Question

I have a table DEAL and a table DEAL_TYPE. I would like to map this code:

public class Deal {
   DealType type;
}

public enum DealType {
   BASE("Base"), EXTRA("Extra");
}

The problem is that the data already exist in the database. And I'm having a hard time mapping the classes to the database.

The database looks something like that:

   TABLE DEAL {
      Long id;
      Long typeId;
   }

   TABLE DEAL_TYPE {
       Long id;
       String text;
   }

I know I could use a simple @OneToMany relationship from deal to deal type, but I would prefer to use an enum. Is this possible?

I almost got it working by using a EnumType.ORDINAL type. But unfortunately, my IDs in my deal type table are not sequential, and do not start at 1.

Any suggestions?

Answer 1

Hibernate is kind of terrible at Enums. It's a strange failing of an otherwise pretty good ORM. The "easiest" way to get around it is to declare your Enum a custom hibernate type. Fortunately, Hibernate wrote an example implementation which you can crib verbatim into your app:

http://www.hibernate.org/265.html

They even include instructions on how to use it. This is the pattern I use whenever I end up with the need to persist enums.

Answer 2

I've created a similar class like the one suggested by hibernate only that is configurable and there is no need to create a new type only for this persistence.

Can be used like

@Type(type = "ro.raisercostin.hibernate.EnumUserType", parameters = @Parameter(name = "type", value = "DealType"))
DealType dealType;

I added an implementation of ParameterizedType to support the passed parameter.

public class EnumUserType implements UserType, ParameterizedType {

    private static final int[] SQL_TYPES = { Types.VARCHAR };
    private Class clazz = null;

    public EnumUserType() {
    }

    @Override
    public void setParameterValues(Properties parameters) {
        String className = (String) parameters.get("type");
        try {
            this.clazz = Class.forName(className);
        } catch (ClassNotFoundException e) {
            throw new RuntimeException("Couldn't get the class for name [" + className + "].", e);
        }
    }

    public int[] sqlTypes() {
        return SQL_TYPES;
    }

    public Class returnedClass() {
        return clazz;
    }

    public Object nullSafeGet(ResultSet resultSet, String[] names, Object owner) throws HibernateException,
            SQLException {
        String name = resultSet.getString(names[0]);
        Object result = null;
        if (!resultSet.wasNull()) {
            result = Enum.valueOf(clazz, name);
        }
        return result;
    }

    public void nullSafeSet(PreparedStatement preparedStatement, Object value, int index) throws HibernateException,
            SQLException {
        if (null == value) {
            preparedStatement.setNull(index, Types.VARCHAR);
        } else {
            preparedStatement.setString(index, ((Enum) value).name());
        }
    }

    public Object deepCopy(Object value) throws HibernateException {
        return value;
    }

    public boolean isMutable() {
        return false;
    }

    public Object assemble(Serializable cached, Object owner) throws HibernateException {
        return cached;
    }

    public Serializable disassemble(Object value) throws HibernateException {
        return (Serializable) value;
    }

    public Object replace(Object original, Object target, Object owner) throws HibernateException {
        return original;
    }

    public int hashCode(Object x) throws HibernateException {
        return x.hashCode();
    }

    public boolean equals(Object x, Object y) throws HibernateException {
        if (x == y) {
            return true;
        }
        if ((null == x) || (null == y)) {
            return false;
        }
        return x.equals(y);
    }
}

Answer 3

You could annotate the enum with @Entity and use a custoumn tuplizer to create the instances of the enum with Enum.valueOf

The enum declaration then looks like:

@Entity
@Table(name = "node_interface_type")
@Tuplizer(impl = EnumTuplizer.class)
public enum Type {
    WIRED, WIRELESS, WIRELESS_SENSOR_NODE;
    @Id
    public String name = toString();
}

And the Tuplizer is:

public class EnumTuplizer extends PojoEntityTuplizer {
    public EnumTuplizer(EntityMetamodel entityMetamodel, PersistentClass mappedEntity) {
        super(entityMetamodel, mappedEntity);
    }

    @Override
    protected Instantiator buildInstantiator(final PersistentClass persistentClass) {
        return new Instantiator() {
            @Override
            public Object instantiate(Serializable id) {
                try {
                    return Enum.valueOf(
                            (Class) persistentClass.getClass().getClassLoader().loadClass(persistentClass.getClassName()),
                            (String) id
                    );
                } catch (ClassNotFoundException e) {
                    throw new AssertionError(e);
                }
            }

            @Override
            public Object instantiate() {
                throw new UnsupportedOperationException();
            }

            @Override
            public boolean isInstance(Object object) {
                throw new UnsupportedOperationException();
            }
        };
    }
}

Answer 4

If you want to use the entity just read-only, then you can use @Formula and @Enumerated . Try something like:

@Entity
public class Deal {
   @Formula("(select text from DEAL_TYPE dt where dt.id = typeId)")
   @Enumerated(EnumType.STRING)
   DealType type;
}

Answer 5

虽然远非理想，但我对此问题的解决方案是使用EnumStringType和非规范化可更新视图。