根據(jù)hibernate的文檔，有兩種方式實(shí)現(xiàn)實(shí)體對(duì)象的主鍵自動(dòng)增長(zhǎng)。
第一種：設(shè)置ID的增長(zhǎng)策略是sequence，同時(shí)指定sequence的名字，最好每個(gè)表建一個(gè)sequence，此種做法就如同MS-SQL,MY-SQL中的自動(dòng)增長(zhǎng)一樣，不需要?jiǎng)?chuàng)建觸發(fā)器，具體的oracle數(shù)據(jù)庫(kù)腳本及hibernate配置文件如下：
oracle數(shù)據(jù)表的創(chuàng)建腳本：
CREATE TABLE DEPARTMENT (
ID NUMBER(19,0) DEFAULT '0' NOT NULL,
NAME VARCHAR2(255) NOT NULL,
DESCRIPTION CLOB
);
ALTER TABLE DEPARTMENT ADD CONSTRAINT PRIMARY_0 PRIMARY KEY(ID) ENABLE;
ALTER TABLE DEPARTMENT ADD CONSTRAINT UK_DEPARTMENT_1 UNIQUE (NAME);
CREATE SEQUENCE DEPARTMENT_ID_SEQ MINVALUE 10000 MAXVALUE 999999999999999999999999 INCREMENT BY 1 NOCYCLE;
CREATE TABLE DEPARTMENT (
ID NUMBER(19,0) DEFAULT '0' NOT NULL,
NAME VARCHAR2(255) NOT NULL,
DESCRIPTION CLOB
);
ALTER TABLE DEPARTMENT ADD CONSTRAINT PRIMARY_0 PRIMARY KEY(ID) ENABLE;
ALTER TABLE DEPARTMENT ADD CONSTRAINT UK_DEPARTMENT_1 UNIQUE (NAME);
CREATE SEQUENCE DEPARTMENT_ID_SEQ MINVALUE 10000 MAXVALUE 999999999999999999999999 INCREMENT BY 1 NOCYCLE;
創(chuàng)建DEPARTMENT表，并為DEPARTMENT表創(chuàng)建一個(gè)單獨(dú)的SEQUENCE，名字為SEQUENCE_ID_SEQ，并不需要?jiǎng)?chuàng)建觸發(fā)器。
[2]hibernate映射文件的配置：
Java代碼
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"
<hibernate-mapping package="com.liyanframework.demo.domain">
<class name="Department" table="DEPARTMENT">
<id name="id" column="ID">
<generator class="sequence">
<param name="sequence">DEPARTMENT_ID_SEQ</param>
</generator>
</id>
<property name="name" column="NAME" type="string" />
<property name="description" column="DESCRIPTION" type="text" />
</class>
</hibernate-mapping>
在hibernate映射文件中，對(duì)ID的生成策略選擇sequence，指定sequence的名字DEPARTMENT_ID_SEQ
就可以了，當(dāng)你保存新對(duì)象的時(shí)候，hibernate會(huì)自動(dòng)取得DEPARTMENT_ID_SEQ.NEXTVAL作為新對(duì)象的ID保存到數(shù)據(jù)庫(kù)，所以
不需要再使用觸發(fā)器再來(lái)生成新記錄的ID。
[/list]
第二種：設(shè)置ID的增長(zhǎng)策略是native，但是需要?jiǎng)?chuàng)建一個(gè)名字為
hibernate_sequence（這個(gè)名字好像是hibernate默認(rèn)的sequence名字，不創(chuàng)建會(huì)出錯(cuò)的）的全局使用的sequence，
然后再對(duì)每一個(gè)表的ID生成的時(shí)候，使用觸發(fā)器，取得hibernate_sequence.CURRVAL作為新記錄的ID，具體的oracle數(shù)據(jù)庫(kù)
腳本及hibernate配置文件如下：
[list]
[1]oracle數(shù)據(jù)表的創(chuàng)建腳本：
Java代碼
CREATE TABLE STAFF (
ID NUMBER(19,0) DEFAULT '0' NOT NULL,
NAME VARCHAR2(255) NOT NULL,
AGE NUMBER(3,0) NOT NULL,
BIRTHDAY DATE NOT NULL,
SALARY NUMBER(10,2) NOT NULL,
LEVELNESS FLOAT NOT NULL,
CREATETIME TIMESTAMP NOT NULL,
ENABLE CHAR(2) DEFAULT 'Y' NOT NULL,
STATUS VARCHAR2(64) NOT NULL,
DEPARTMENT_ID NUMBER(19,0)
);
ALTER TABLE STAFF ADD CONSTRAINT PRIMARY_1 PRIMARY KEY(ID) ENABLE;
ALTER TABLE STAFF ADD CONSTRAINT STAFF_IBFK_0 FOREIGN KEY(DEPARTMENT_ID) REFERENCES DEPARTMENT(ID) ENABLE;
ALTER TABLE STAFF ADD CONSTRAINT UK_STAFF_1 UNIQUE (NAME);
CREATE INDEX IDX_STAFF_STATUS ON STAFF(STATUS);
CREATE SEQUENCE HIBERNATE_SEQUENCE MINVALUE 90000 MAXVALUE 999999999999999999999999 INCREMENT BY 1 NOCYCLE;
CREATE OR REPLACE TRIGGER STAFF_ID_TRG BEFORE INSERT ON STAFF
FOR EACH ROW
BEGIN
IF INSERTING AND :NEW.ID IS NULL THEN
SELECT HIBERNATE_SEQUENCE.CURRVAL INTO :NEW.ID FROM DUAL;
END IF;
END;
CREATE TABLE STAFF (
ID NUMBER(19,0) DEFAULT '0' NOT NULL,
NAME VARCHAR2(255) NOT NULL,
AGE NUMBER(3,0) NOT NULL,
BIRTHDAY DATE NOT NULL,
SALARY NUMBER(10,2) NOT NULL,
LEVELNESS FLOAT NOT NULL,
CREATETIME TIMESTAMP NOT NULL,
ENABLE CHAR(2) DEFAULT 'Y' NOT NULL,
STATUS VARCHAR2(64) NOT NULL,
DEPARTMENT_ID NUMBER(19,0)
);
ALTER TABLE STAFF ADD CONSTRAINT PRIMARY_1 PRIMARY KEY(ID) ENABLE;
ALTER TABLE STAFF ADD CONSTRAINT STAFF_IBFK_0 FOREIGN KEY(DEPARTMENT_ID) REFERENCES DEPARTMENT(ID) ENABLE;
ALTER TABLE STAFF ADD CONSTRAINT UK_STAFF_1 UNIQUE (NAME);
CREATE INDEX IDX_STAFF_STATUS ON STAFF(STATUS);
CREATE SEQUENCE HIBERNATE_SEQUENCE MINVALUE 90000 MAXVALUE 999999999999999999999999 INCREMENT BY 1 NOCYCLE;
CREATE OR REPLACE TRIGGER STAFF_ID_TRG BEFORE INSERT ON STAFF
FOR EACH ROW
BEGIN
IF INSERTING AND :NEW.ID IS NULL THEN
SELECT HIBERNATE_SEQUENCE.CURRVAL INTO :NEW.ID FROM DUAL;
END IF;
END;
創(chuàng)建STAFF表，但是并沒(méi)有為STAFF創(chuàng)建相應(yīng)的主鍵sequence，而是創(chuàng)建了一個(gè)名字為HIBERNATE_SEQUENCE的
sequence，然后創(chuàng)建一個(gè)觸發(fā)器STAFF_ID_TRG，當(dāng)執(zhí)行INSERT操作時(shí)，hibernate會(huì)先執(zhí)行一次
HIBERNATE_SEQUENCE.NEXTVAL，所以在觸發(fā)器中只需要取得HIBERNATE_SEQUENCE.CURRVAL作為新記錄的
ID。
[2]hibernate映射文件的配置：
Java代碼
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"
<hibernate-mapping package="com.liyanframework.demo.domain">
<class name="Staff" table="STAFF">
<id name="id" column="ID">
<generator class="native" />
</id>
<property name="name" column="NAME" type="string" />
<property name="age" column="AGE" type="integer" />
<property name="birthday" column="BIRTHDAY" type="date" />
<property name="salary" column="SALARY" type="big_decimal" />
<property name="level" column="LEVELNESS" type="float" />
<property name="createTime" column="CREATETIME" type="timestamp" />
<property name="enable" column="ENABLE" type="character" />
<property name="status" column="STATUS" type="string" />
<many-to-one name="department" column="DEPARTMENT_ID" class="Department" />
</class>
</hibernate-mapping>
在hibernate映射文件中，對(duì)ID的生成策略選擇native，hibernate會(huì)根據(jù)你數(shù)據(jù)庫(kù)的觸發(fā)器來(lái)生成新記錄的ID。[/list]
比
較兩種做法，第二種做法也就是hibernate在代碼中，實(shí)現(xiàn)了oracle中的觸發(fā)器功能。對(duì)于不同的情況，選擇不懂的做法。如果新的系統(tǒng)，新建的
oracle數(shù)據(jù)庫(kù)，推薦使用第一種做法，簡(jiǎn)單，容易移植到其他支持自動(dòng)增長(zhǎng)的數(shù)據(jù)庫(kù)；如果是老的系統(tǒng)，需要把其他數(shù)據(jù)庫(kù)轉(zhuǎn)換為oracle的，那就要用
第二種了，使用native的方式，可以不改動(dòng)配置文件，兼容oracle和mysql之類帶有自動(dòng)增長(zhǎng)的數(shù)據(jù)庫(kù)。