Hibernate-Java-SQL type ing table and hibernate identity Generation Policy

I. hibernate-Java-SQL type ing table

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Basic hibernate type	Java type	Standard SQL Field Type	Size/Description
Big_decimal	Java. Math. bigdecimal	Numeric	Precision value (8 bits)
Binary	Byte []	Varbinary, blob	Variable-length binary data
Blob	Java. SQL. blob	Blob	Binary data
Boolean	Boolean/Java. Lang. Boolean	Bit	Boolean Type
Byte	Byte/Java. Lang. byte	Tinyint	1 byte
Calender	Java. util. Calendar	Timestamp	Long date (yyyymmddhhmmss)
Calender_date	Java. util. Calendar	Date	YYYY-MM-DD (short date)
Character	Java. Lang. Character/Java. Lang. String/Char	Char (1)	Fixed Length character
Class	Java. Lang. Class	Varchar	Variable-length characters
Clob	Java. SQL. clob	Clob	Clob
Currency	Java. util. Currency	Varchar	Fixed Length character
Date	Java. util. Date/Java. SQL. Date	Date	Date
Double	Double/Java. Lang. Double	Double	8 bytes
Float	Float/Java. Lang. Float	Float	4 bytes
Interger	INT/Java. langinteger	Integer	4 bytes
Local	Java. util. locale	Varchar	Variable-length characters
Long	Long/Java. Lang. Long	Bigint	8 bytes
Seralizable	Java. Io. serializable and so on	Varbinary, blob	Variable-length binary data
Short	Short/Java. Lang. Short	Smallint	2 bytes
String	Java. Lang. String	Varchar	Variable-length characters
Text	Java. Lang. String	Clob	Large Character object
Time	Java. util. Date/Java. SQL. Time	Time	Time (HH: mm: SS)
Timestamp	Java. util. Date/Java. SQL. Timestamp	Timestamp	YYYY-MM-DD (short date)
Timezone	Java. util. timezone	Varchar	Variable-length characters
True_false	Boolean/Java. langboolean	Char (1) ('T'/'F ')	Boolean Type
Yes_no	Boolean/Java. Lang. Boolean	Char (1) ('y'/'n ')	Boolean Type
Note: 1. considering that the operations on BLOB fields are too complicated, the technique of a transformation is. the object class uses the byte [] type, the hibernate type uses binary, and the database uses blob. this can simplify some operations; 2. type is of the string type. Because there is no text type in Java, the varchar type field and text type field in MySQL are both strings in the ing file in Java and the JavaBean field, but the length is limited, generally, the maximum length of text fields in the Java ing file is 65535.

I. hibernate identity Generation Policy

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Identifier Generator	Description
Increment (incremental)	Applies to the proxy primary key. It is automatically generated by hibernate in incremental mode. Used for long, short, or Int type. It can be used only when no other process inserts data into the same table. Do not use it in a cluster.
Identity	Applies to the proxy primary key. The identifier generated by the underlying database. Supports built-in identity fields for DB2, MySQL, ms SQL Server, Sybase, and hypersonicsql. The returned identifier is of the long, short, or Int type.
Sequence)	Applies to the proxy primary key. Hibernate generates identifiers Based on the sequence of the underlying database, which requires that the underlying database supports sequences. Sequence is used in DB2, PostgreSQL, Oracle, sap db, and mckoi, while generator is used in InterBase ). The returned identifier is of the long, short, or Int type.
HiLo (high/low)	Applies to the proxy primary key. The identifier generated by the high/low algorithm of the hibernate branch. Use a high/low algorithm to efficiently generate long, short, or Int type identifiers. Specify a table and field (hibernate_unique_key and next_hi by default) as the source of high value. The inherent identifiers of high/low algorithms are unique only in a specific database. Do not use this native tool in the connection obtained by using JTA or the connection provided by the user.
Seqhilo (using the high and low bits of the sequence)	Applies to the proxy primary key. Use a high/low-level algorithm to efficiently generate long, short, or Int type identifiers, and specify the name of a database sequence (sequence.
UUID. HEX	Applies to the proxy primary key. Hibernate uses the 128-bit UUID algorithm to generate string-type identifiers. It is unique in a network (using an IP address ). UUID is encoded as a 32-bit hexadecimal number string.
UUID. String	Applies to the proxy primary key. UUID is encoded into a 16-character string. The same UUID algorithm is used. UUID is encoded as a string consisting of 16 characters long and any ASCII characters. Cannot be used in a PostgreSQL database.
Native (local)	Applies to the proxy primary key. Automatically select one of identity, sequence, or HiLo based on the method in which the underlying database automatically generates identifiers.
Assigned (program settings)	Applicable to natural primary keys. The Java application is responsible for generating identifiers. Assign an identifier to the object before saving.
Foreign (External Reference)	Applies to the proxy primary key. Use the identifier of another associated object.
Select	Added in hibernate3. You must provide a unique identification field for secondary reading to obtain the inherent primary key value of the trigger and define it through the param sub-element. This method mainly targets legacy system transformation projects. Some early system primary keys rely on the trigger. When the database is inserted, the trigger captures this operation and assigns a value to the primary key. After inserting the data into the database, it reads a recognition field again to read the inserted data and obtain its primary key value.
Remarks: Composite primary key ing <Composite-ID> <Key-property? Column = "userid "? Name = "userid "? Type = "Java. Lang. String"> </key-property> <Key-property? Column = "when "? Name = "when "? Type = "Java. SQL. Date"> </key-property> </Composite-ID> The pojo class of the composite primary key needs to implement the equals and hashcode methods, you can use the tool class implementation in the Apache commons lang Package (commons-lang.jar) Iii. hibernate ing between Java time and date types Hibernate ing type Java type Standard SQL type Description Date Util. Date or SQL. Date Date YYYY-MM-DD Time Date time Time Hh: mm: SS Timestamp Date Timestamp Timestamp Yyyymmddhhmmss Calendar Calendar Timestamp Yyyymmddhhmmss Calendar_date Calendar Date YYYY-MM-DD