Hibernate对象映射类型

Basic value types usually map a single database value, or column, to a single, non-aggregated Java type. Hibernate provides a number of built-in basic types, which follow the natural mappings recommended in the JDBC specifications. You can override these mappings and provide and use alternative mappings. These topics are discussed further on.

National Character types, which is a new feature since JDBC 4.0 API, now available in hibernate type system. National Language Support enables you retrieve data or insert data into a database in any character set that the underlying database supports.

Depending on your environment, you might want to set the configuration option hibernate.use_nationalized_character_data to true and having all string or clob based attributes having this national character support automatically. There is nothing else to be changed, and you don‘t have to use any hibernate specific mapping, so it is portable ( though the national character support feature is not required and may not work on other JPA provider impl ).

The other way of using this feature is having the @Nationalized annotation on the attribute that should be nationalized. This only works on string based attributes, including string, char, char array and clob.

                @Entity( name="NationalizedEntity")
                public static class NationalizedEntity {
                    @Id
                    private Integer id;

                    @Nationalized
                    private String nvarcharAtt;

                    @Lob
                    @Nationalized
                    private String materializedNclobAtt;

                    @Lob
                    @Nationalized
                    private NClob nclobAtt;

                    @Nationalized
                    private Character ncharacterAtt;

                    @Nationalized
                    private Character[] ncharArrAtt;

                    @Type(type = "ntext")
                    private String nlongvarcharcharAtt;
                }

Composite types, or embedded types, as they are called by the Java Persistence API, have traditionally been called components in Hibernate. All of these terms mean the same thing.

Components represent aggregations of values into a single Java type. An example is an Address class, which aggregates street, city, state, and postal code. A composite type behaves in a similar way to an entity. They are each classes written specifically for an application. They may both include references to other application-specific classes, as well as to collections and simple JDK types. The only distinguishing factors are that a component does not have its own lifecycle or define an identifier.

A collection type refers to the data type itself, not its contents.

A Collection denotes a one-to-one or one-to-many relationship between tables of a database.

Refer to the chapter on Collections for more information on collections.