Hibernate mapped data types! (change)

Hibernate mapping types are divided into two types: built-in mapping types and customized mapping types. The built-in mapping type is responsible for mapping some common Java types to the corresponding SQL types; in addition, Hibernate also allows users to implement the UserType or CompositeUserType interface to flexibly customize customized mapping types

1. Built-in mapping Type
   1).Hibernate mapping type of Java basic type

Java types	Hibernate mapping type	Standard SQL types	Size and value range
int/Integer	int/integer	INTEGER	4Byte
long/Long	long	BIGINT	8Byte
short/Short	short	SAMLLINT	2Byte
exchange/Exchange	byte	TINYINT	1Byte
float/Float	float	FLOAT	4Byte
double/Double	double	DOUBLE	8Byte
BigDecimal	big_decimal	NUMBERIC	Numeric(8,2)
char/Character/String	character	CHAR(1)	Fixed length characters
String	string	VARCHAR	variable length characters
boolean/Boolean	boolean	BIT	Boolean type
boolean/Boolean	yes/no	CHAR(1)('Y'/'N')	Boolean type
boolean/Boolean	true/false	CHAR(1)('T'/'F')	Boolean type

    2). Hibernate mapping type of Java time and date types

Java types	Hibernate mapping type	Standard SQL types	describe
java.util.Date/java.sql.Date	date	DATE	Date, yyyy-mm-dd
java.util.Date/java.sql.TIme	time	TIME	Time,hh:mm:ss
java.util.Date/java.sql.Timestamp	timestamp	TIMESTAMP	Timestamp, yyyymmddhhmmss
java.util.Calendar	calendar	TIMESTAMP	Same as above
java.util.Calendar	calendar_date	DATE	Date, yyyy-mm-dd

* When the program type is java.sql.Timestamp and the table attribute type in the database is timestamp, even if the user inserts data with a null value, the database system will still automatically fill in the timestamp value

    3). Hibernate mapping type of Java large object type

Java types	Hibernate mapping type	Standard SQL types	MySql type	Oracle type
byte[]	binary	VARBINARY/BLOB	BLOB	BLOB
String	text	CLOB	TEXT	CLOB
serializable	A java class that implements the serializable interface	VARBINARY/BLOB	BLOB	BLOB
java.sql.Clob	clob	CLOB	TEXT	CLOB
java.sql.Blob	blob	BLOB	BLOB	BLOB

* When saving java.sql.Clob or java.sql.Blob instances through Hibernate in an application, two steps must be included:
        a. In a database transaction First save an empty Blob or Clob instance; b. Then lock this record, update the Blob or Clob instance saved in step (1), and write binary data or long text data to the Blob or Clob instance.

 1
 2 Session session  =  sessionFactory.openSession();
 3 Transaction tx  =  session.beginTransaction();
 4 Customer customer  =   new  Customer();
 5 customer.setDescription(Hibernate.createClob( "" ));  // 先保存一个空的clob
 6 session.save(customer);
 7 session.flush();
 8 // 锁定这条记录
 9 session.refresh(customer,LockMode.UPGRADE);
10 oracle.sql.CLOB clob  =  (oracle.sql.CLOB) customer.getDescription();
11 java.io.Writer pw  =  clob.getCharacterOutStream();
12 pw.write(longText); // longText是一个长度超过255的字符串
13 pw.close();
14 tx.commit();
15 session.close();

* When one java type corresponds to multiple Hibernate mapping types. For example, if the attribute of the persistence class is of type java.util.Date, the corresponding Hibernate mapping type can be date, time
or timestamp. At this time, the Hibernate mapping type must be determined based on the SQL type of the corresponding database table field. If the field is of type Date, hibernate maps it to datge, if it is TIME it is time, if it is TIMESTAMP it is timestamp.