Data_Categorizations.xml

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<chapter xmlns="http://docbook.org/ns/docbook">

  <title>Data categorizations</title>
  <para>
    Hibernate understands both the Java and JDBC representations of application data. The ability to read and write
    object data to a database is called <firstterm>marshalling</firstterm>, and is the function of a Hibernate
    <classname>type</classname>. A <classname>type</classname> is an implementation of the
    <interfacename>org.hibernate.type.Type</interfacename> interface. A Hibernate <classname>type</classname> describes
    various aspects of behavior of the Java type such as how to check for equality and how to clone values.
  </para>
  <note>
    <title>Usage of the word <wordasword>type</wordasword></title>
    <para>
      A Hibernate <classname>type</classname> is neither a Java type nor a SQL datatype. It provides information about
      both of these.
    </para>
    <para>
      When you encounter the term <firstterm>type</firstterm> in regards to Hibernate, it may refer to the Java type,
      the JDBC type, or the Hibernate type, depending on context.
    </para>
  </note>
  <para>
    Hibernate categorizes types into two high-level groups: <xref linkend="value-types" />
      and <xref linkend="entity-types" />.
  </para>
  
  <section xml:id="value-types">
    <title>Value types</title>
    <para>
      A <firstterm>value type</firstterm> does not define its own lifecycle. It is, in effect, owned by an <xref
      linkend="entity-types" />, which defines its
      lifecycle. Value types are further classified into three sub-categories.
    </para>
    <itemizedlist>
      <listitem><para><xref linkend="value-basic-types" /></para></listitem>
        <listitem><para><xref linkend="value-national-character-types" /></para></listitem>
      <listitem><para><xref linkend="value-composite-types" /></para></listitem>
      <listitem><para><xref linkend="value-collection-types" /></para></listitem>
    </itemizedlist>

    <section xml:id="value-basic-types">
      <title>Basic types</title>
      <para>
        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.
      </para>
      <table>
        <title>Basic Type Mappings</title>
        <tgroup cols="4">
          <thead>
            <row>
              <entry>Hibernate type</entry>
              <entry>Database type</entry>
              <entry>JDBC type</entry>
              <entry>Type registry</entry>
            </row>
          </thead>
          <tbody>
            <row>
              <entry>org.hibernate.type.StringType</entry>
              <entry>string</entry>
              <entry>VARCHAR</entry>
              <entry>string, java.lang.String</entry>
            </row>
            <row>
              <entry>org.hibernate.type.MaterializedClob</entry>
              <entry>string</entry>
              <entry>CLOB</entry>
              <entry>materialized_clob</entry>
            </row>
            <row>
              <entry>org.hibernate.type.TextType</entry>
              <entry>string</entry>
              <entry>LONGVARCHAR</entry>
              <entry>text</entry>
            </row>
            <row>
              <entry>org.hibernate.type.CharacterType</entry>
              <entry>char, java.lang.Character</entry>
              <entry>CHAR</entry>
              <entry>char, java.lang.Character</entry>
            </row>
            <row>
              <entry>org.hibernate.type.BooleanType</entry>
              <entry>boolean</entry>
              <entry>BIT</entry>
              <entry>boolean, java.lang.Boolean</entry>
            </row>
            <row>
              <entry>org.hibernate.type.NumericBooleanType</entry>
              <entry>boolean</entry>
              <entry>INTEGER, 0 is false, 1 is true</entry>
              <entry>numeric_boolean</entry>
            </row>
            <row>
              <entry>org.hibernate.type.YesNoType</entry>
              <entry>boolean</entry>
              <entry>CHAR, 'N'/'n' is false, 'Y'/'y' is true. The uppercase value is written to the database.</entry>
              <entry>yes_no</entry>
            </row>
            <row>
              <entry>org.hibernate.type.TrueFalseType</entry>
              <entry>boolean</entry>
              <entry>CHAR, 'F'/'f' is false, 'T'/'t' is true. The uppercase value is written to the database.</entry>
              <entry>true_false</entry>
            </row>
            <row>
              <entry>org.hibernate.type.ByteType</entry>
              <entry>byte, java.lang.Byte</entry>
              <entry>TINYINT</entry>
              <entry>byte, java.lang.Byte</entry>
            </row>
            <row>
              <entry>org.hibernate.type.ShortType</entry>
              <entry>short, java.lang.Short</entry>
              <entry>SMALLINT</entry>
              <entry>short, java.lang.Short</entry>
            </row>
            <row>
              <entry>org.hibernate.type.IntegerTypes</entry>
              <entry>int, java.lang.Integer</entry>
              <entry>INTEGER</entry>
              <entry>int, java.lang.Integer</entry>
            </row>
            <row>
              <entry>org.hibernate.type.LongType</entry>
              <entry>long, java.lang.Long</entry>
              <entry>BIGINT</entry>
              <entry>long, java.lang.Long</entry>
            </row>
            <row>
              <entry>org.hibernate.type.FloatType</entry>
              <entry>float, java.lang.Float</entry>
              <entry>FLOAT</entry>
              <entry>float, java.lang.Float</entry>
            </row>
            <row>
              <entry>org.hibernate.type.DoubleType</entry>
              <entry>double, java.lang.Double</entry>
              <entry>DOUBLE</entry>
              <entry>double, java.lang.Double</entry>
            </row>
            <row>
              <entry>org.hibernate.type.BigIntegerType</entry>
              <entry>java.math.BigInteger</entry>
              <entry>NUMERIC</entry>
              <entry>big_integer</entry>
            </row>
            <row>
              <entry>org.hibernate.type.BigDecimalType</entry>
              <entry>java.math.BigDecimal</entry>
              <entry>NUMERIC</entry>
              <entry>big_decimal, java.math.bigDecimal</entry>
            </row>
            <row>
              <entry>org.hibernate.type.TimestampType</entry>
              <entry>java.sql.Timestamp</entry>
              <entry>TIMESTAMP</entry>
              <entry>timestamp, java.sql.Timestamp</entry>
            </row>
            <row>
              <entry>org.hibernate.type.TimeType</entry>
              <entry>java.sql.Time</entry>
              <entry>TIME</entry>
              <entry>time, java.sql.Time</entry>
            </row>
            <row>
              <entry>org.hibernate.type.DateType</entry>
              <entry>java.sql.Date</entry>
              <entry>DATE</entry>
              <entry>date, java.sql.Date</entry>
            </row>
            <row>
              <entry>org.hibernate.type.CalendarType</entry>
              <entry>java.util.Calendar</entry>
              <entry>TIMESTAMP</entry>
              <entry>calendar, java.util.Calendar</entry>
            </row>
            <row>
              <entry>org.hibernate.type.CalendarDateType</entry>
              <entry>java.util.Calendar</entry>
              <entry>DATE</entry>
              <entry>calendar_date</entry>
            </row>
            <row>
              <entry>org.hibernate.type.CurrencyType</entry>
              <entry>java.util.Currency</entry>
              <entry>VARCHAR</entry>
              <entry>currency, java.util.Currency</entry>
            </row>
            <row>
              <entry>org.hibernate.type.LocaleType</entry>
              <entry>java.util.Locale</entry>
              <entry>VARCHAR</entry>
              <entry>locale, java.utility.locale</entry>
            </row>
            <row>
              <entry>org.hibernate.type.TimeZoneType</entry>
              <entry>java.util.TimeZone</entry>
              <entry>VARCHAR, using the TimeZone ID</entry>
              <entry>timezone, java.util.TimeZone</entry>
            </row>
            <row>
              <entry>org.hibernate.type.UrlType</entry>
              <entry>java.net.URL</entry>
              <entry>VARCHAR</entry>
              <entry>url, java.net.URL</entry>
            </row>
            <row>
              <entry>org.hibernate.type.ClassType</entry>
              <entry>java.lang.Class</entry>
              <entry>VARCHAR, using the class name</entry>
              <entry>class, java.lang.Class</entry>
            </row>
            <row>
              <entry>org.hibernate.type.BlobType</entry>
              <entry>java.sql.Blob</entry>
              <entry>BLOB</entry>
              <entry>blog, java.sql.Blob</entry>
            </row>
            <row>
              <entry>org.hibernate.type.ClobType</entry>
              <entry>java.sql.Clob</entry>
              <entry>CLOB</entry>
              <entry>clob, java.sql.Clob</entry>
            </row>
            <row>
              <entry>org.hibernate.type.BinaryType</entry>
              <entry>primitive byte[]</entry>
              <entry>VARBINARY</entry>
              <entry>binary, byte[]</entry>
            </row>
            <row>
              <entry>org.hibernate.type.MaterializedBlobType</entry>
              <entry>primitive byte[]</entry>
              <entry>BLOB</entry>
              <entry>materized_blob</entry>
            </row>
            <row>
              <entry>org.hibernate.type.ImageType</entry>
              <entry>primitive byte[]</entry>
              <entry>LONGVARBINARY</entry>
              <entry>image</entry>
            </row>
            <row>
              <entry>org.hibernate.type.BinaryType</entry>
              <entry>java.lang.Byte[]</entry>
              <entry>VARBINARY</entry>
              <entry>wrapper-binary</entry>
            </row>
            <row>
              <entry>org.hibernate.type.CharArrayType</entry>
              <entry>char[]</entry>
              <entry>VARCHAR</entry>
              <entry>characters, char[]</entry>
            </row>
            <row>
              <entry>org.hibernate.type.CharacterArrayType</entry>
              <entry>java.lang.Character[]</entry>
              <entry>VARCHAR</entry>
              <entry>wrapper-characters, Character[], java.lang.Character[]</entry>
            </row>
            <row>
              <entry>org.hibernate.type.UUIDBinaryType</entry>
              <entry>java.util.UUID</entry>
              <entry>BINARY</entry>
              <entry>uuid-binary, java.util.UUID</entry>
            </row>
            <row>
              <entry>org.hibernate.type.UUIDCharType</entry>
              <entry>java.util.UUID</entry>
              <entry>CHAR, can also read VARCHAR</entry>
              <entry>uuid-char</entry>
            </row>
            <row>
              <entry>org.hibernate.type.PostgresUUIDType</entry>
              <entry>java.util.UUID</entry>
              <entry>PostgreSQL UUID, through Types#OTHER, which complies to the PostgreSQL JDBC driver
              definition</entry>
              <entry>pg-uuid</entry>
            </row>
            <row>
              <entry>org.hibernate.type.SerializableType</entry>
              <entry>implementors of java.lang.Serializable</entry>
              <entry>VARBINARY</entry>
              <entry> Unlike the other value types, multiple instances of this type are registered. It is registered
              once under java.io.Serializable, and registered under the specific java.io.Serializable implementation
              class names.</entry>
            </row>
          </tbody>
        </tgroup>
      </table>
    </section>
    <section xml:id="value-national-character-types">
        <title>National Character Types</title>
        <para>
            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.
        </para>

        <para>
            Depending on your environment, you might want to set the configuration option <property>hibernate.use_nationalized_character_data</property>
            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 ).
        </para>

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

            <programlisting role="JAVA">
                @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;
                }</programlisting>
        </para>

        <table>
            <title>National Character Type Mappings</title>
            <tgroup cols="4">
                <thead>
                    <row>
                        <entry>Hibernate type</entry>
                        <entry>Database type</entry>
                        <entry>JDBC type</entry>
                        <entry>Type registry</entry>
                    </row>
                </thead>
                <tbody>
                    <row>
                        <entry>org.hibernate.type.StringNVarcharType</entry>
                        <entry>string</entry>
                        <entry>NVARCHAR</entry>
                        <entry>nstring</entry>
                    </row>
                    <row>
                        <entry>org.hibernate.type.NTextType</entry>
                        <entry>string</entry>
                        <entry>LONGNVARCHAR</entry>
                        <entry>materialized_clob</entry>
                    </row>
                    <row>
                        <entry>org.hibernate.type.NClobType</entry>
                        <entry>java.sql.NClob</entry>
                        <entry>NCLOB</entry>
                        <entry>nclob</entry>
                    </row>
                    <row>
                        <entry>org.hibernate.type.MaterializedNClobType</entry>
                        <entry>string</entry>
                        <entry>NCLOB</entry>
                        <entry>materialized_nclob</entry>
                    </row>
                    <row>
                        <entry>org.hibernate.type.PrimitiveCharacterArrayNClobType</entry>
                        <entry>char[]</entry>
                        <entry>NCHAR</entry>
                        <entry>char[]</entry>
                    </row>
                    <row>
                        <entry>org.hibernate.type.CharacterNCharType</entry>
                        <entry>java.lang.Character</entry>
                        <entry>NCHAR</entry>
                        <entry>ncharacter</entry>
                    </row>
                    <row>
                        <entry>org.hibernate.type.CharacterArrayNClobType</entry>
                        <entry>java.lang.Character[]</entry>
                        <entry>NCLOB</entry>
                        <entry>Character[], java.lang.Character[]</entry>
                    </row>
                </tbody>
            </tgroup>
        </table>
    </section>
    <section xml:id="value-composite-types">
      <title>Composite types</title>
      <para>
        <firstterm>Composite types</firstterm>, or <firstterm>embedded types</firstterm>, as they are called by the Java
        Persistence API, have traditionally been called <firstterm>components</firstterm> in Hibernate. All of these
        terms mean the same thing.
      </para>
      <para>
        Components represent aggregations of values into a single Java type. An example is an
        <classname>Address</classname> 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.
      </para>
      
    </section>
    
    <section xml:id="value-collection-types">
      <title>Collection types</title>
      <para>
        A <firstterm>collection</firstterm> type refers to the data type itself, not its contents.
      </para>
      <para>
        A Collection denotes a one-to-one or one-to-many relationship between tables of a database.
      </para>
      <para>
        Refer to the chapter on Collections for more information on collections.
      </para>
    </section>
  </section>
  <section xml:id="entity-types">
    <title>Entity Types</title>
    <para>
      Entities are application-specific classes which correlate to rows in a table, using a unique identifier. Because
      of the requirement for a unique identifier, ntities exist independently and define their own lifecycle. As an
      example, deleting a Membership should not delete the User or the Group. For more information, see the chapter on
      Persistent Classes.
    </para>
  </section>
  
  <section>
    <title>Implications of different data categorizations</title>
    <para>
      NEEDS TO BE WRITTEN
    </para>
    
  </section>

</chapter>