Hibernate對象映射類型

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Hibernate understands both the Java and JDBC representations of application data. The ability to read and write object data to a database is called marshalling, and is the function of a Hibernate type. A type is an implementation of the org.hibernate.type.Type interface. A Hibernate type describes various aspects of behavior of the Java type such as how to check for equality and how to clone values.

Usage of the word type

A Hibernate type is neither a Java type nor a SQL datatype. It provides information about both of these.

When you encounter the term type in regards to Hibernate, it may refer to the Java type, the JDBC type, or the Hibernate type, depending on context.

1. Value types1.1. Basic types

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.

Table 1.1. Basic Type Mappings

Hibernate type	Database type	JDBC type	Type registry
org.hibernate.type.StringType	string	VARCHAR	string, java.lang.String
org.hibernate.type.MaterializedClob	string	CLOB	materialized_clob
org.hibernate.type.TextType	string	LONGVARCHAR	text
org.hibernate.type.CharacterType	char, java.lang.Character	CHAR	char, java.lang.Character
org.hibernate.type.BooleanType	boolean	BIT	boolean, java.lang.Boolean
org.hibernate.type.NumericBooleanType	boolean	INTEGER, 0 is false, 1 is true	numeric_boolean
org.hibernate.type.YesNoType	boolean	CHAR, ‘N‘/‘n‘ is false, ‘Y‘/‘y‘ is true. The uppercase value is written to the database.	yes_no
org.hibernate.type.TrueFalseType	boolean	CHAR, ‘F‘/‘f‘ is false, ‘T‘/‘t‘ is true. The uppercase value is written to the database.	true_false
org.hibernate.type.ByteType	byte, java.lang.Byte	TINYINT	byte, java.lang.Byte
org.hibernate.type.ShortType	short, java.lang.Short	SMALLINT	short, java.lang.Short
org.hibernate.type.IntegerTypes	int, java.lang.Integer	INTEGER	int, java.lang.Integer
org.hibernate.type.LongType	long, java.lang.Long	BIGINT	long, java.lang.Long
org.hibernate.type.FloatType	float, java.lang.Float	FLOAT	float, java.lang.Float
org.hibernate.type.DoubleType	double, java.lang.Double	DOUBLE	double, java.lang.Double
org.hibernate.type.BigIntegerType	java.math.BigInteger	NUMERIC	big_integer
org.hibernate.type.BigDecimalType	java.math.BigDecimal	NUMERIC	big_decimal, java.math.bigDecimal
org.hibernate.type.TimestampType	java.sql.Timestamp	TIMESTAMP	timestamp, java.sql.Timestamp
org.hibernate.type.TimeType	java.sql.Time	TIME	time, java.sql.Time
org.hibernate.type.DateType	java.sql.Date	DATE	date, java.sql.Date
org.hibernate.type.CalendarType	java.util.Calendar	TIMESTAMP	calendar, java.util.Calendar
org.hibernate.type.CalendarDateType	java.util.Calendar	DATE	calendar_date
org.hibernate.type.CurrencyType	java.util.Currency	VARCHAR	currency, java.util.Currency
org.hibernate.type.LocaleType	java.util.Locale	VARCHAR	locale, java.utility.locale
org.hibernate.type.TimeZoneType	java.util.TimeZone	VARCHAR, using the TimeZone ID	timezone, java.util.TimeZone
org.hibernate.type.UrlType	java.net.URL	VARCHAR	url, java.net.URL
org.hibernate.type.ClassType	java.lang.Class	VARCHAR, using the class name	class, java.lang.Class
org.hibernate.type.BlobType	java.sql.Blob	BLOB	blog, java.sql.Blob
org.hibernate.type.ClobType	java.sql.Clob	CLOB	clob, java.sql.Clob
org.hibernate.type.BinaryType	primitive byte[]	VARBINARY	binary, byte[]
org.hibernate.type.MaterializedBlobType	primitive byte[]	BLOB	materized_blob
org.hibernate.type.ImageType	primitive byte[]	LONGVARBINARY	image
org.hibernate.type.BinaryType	java.lang.Byte[]	VARBINARY	wrapper-binary
org.hibernate.type.CharArrayType	char[]	VARCHAR	characters, char[]
org.hibernate.type.CharacterArrayType	java.lang.Character[]	VARCHAR	wrapper-characters, Character[], java.lang.Character[]
org.hibernate.type.UUIDBinaryType	java.util.UUID	BINARY	uuid-binary, java.util.UUID
org.hibernate.type.UUIDCharType	java.util.UUID	CHAR, can also read VARCHAR	uuid-char
org.hibernate.type.PostgresUUIDType	java.util.UUID	PostgreSQL UUID, through Types#OTHER, which complies to the PostgreSQL JDBC driver definition	pg-uuid
org.hibernate.type.SerializableType	implementors of java.lang.Serializable	VARBINARY	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.

1.2. National Character Types

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;                }

Table 1.2. National Character Type Mappings

Hibernate type	Database type	JDBC type	Type registry
org.hibernate.type.StringNVarcharType	string	NVARCHAR	nstring
org.hibernate.type.NTextType	string	LONGNVARCHAR	materialized_clob
org.hibernate.type.NClobType	java.sql.NClob	NCLOB	nclob
org.hibernate.type.MaterializedNClobType	string	NCLOB	materialized_nclob
org.hibernate.type.PrimitiveCharacterArrayNClobType	char[]	NCHAR	char[]
org.hibernate.type.CharacterNCharType	java.lang.Character	NCHAR	ncharacter
org.hibernate.type.CharacterArrayNClobType	java.lang.Character[]	NCLOB	Character[], java.lang.Character[]

1.3. Composite types

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.

1.4. Collection types

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.

2. Entity Types

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.

 

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Hibernate對象映射類型