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CREATE TABLE Stock (
id BIGINT UNSIGNED NOT NULL PRIMARY KEY AUTO_INCREMENT,
NO VARCHAR(255) NOT NULL,
name VARCHAR(255) NOT NULL,
price DECIMAL(6,2) NOT NULL,
UNIQUE KEY Stock_NO (NO),
INDEX Stock_Name(name)
) ENGINE = InnoDB;
@Entity
@Table(name = "Stock", uniqueConstraints = {
@UniqueConstraint(name = "Stock_NO", columnNames = { "NO" })
},
indexes = {
@Index(name = "Stock_Name", columnList = "name")
})
public class Stock {
private long id;
private String no;
private String name;
private double price;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
public long getId() {
return id;
}
public void setId(long id) {
this.id = id;
} @GeneratedValue(strategy = GenerationType.IDENTITY)：实体主键生成策略是自动生成，兼容MySQL主键自动生成策略，关键词是AUTO_INCREMENT。若是MySQL主键没有指定AUTO_INCREMENT，报出以下异常。javax.persistence.PersistenceException: org.hibernate.exception.GenericJDBCException: could not execute statement Caused by: org.hibernate.exception.GenericJDBCException: could not execute statement Caused by: java.sql.SQLException: Field 'id' doesn't have a default value
<properties>
<property name="javax.persistence.schema-generation.database.action"
value="drop-and-create" />
</properties>模式生成虽然很方便，能自动生成表结构，但是，由它生成的表结构不总是最佳的，而且还不能保证是正确的。因此，作为最佳实践，不建议在生产环境启用模式生成，手工维护表机构。禁用模式生成，在配置文件persistence.xml做如下配置： <properties>
<property name="javax.persistence.schema-generation.database.action"
value="none" />
</properties>
CREATE TABLE CreatorKey ( TableName VARCHAR(64) NOT NULL PRIMARY KEY, KeyValue BIGINT UNSIGNED NOT NULL, INDEX CreatorKey_Table_Values (TableName, KeyValue) ) ENGINE = InnoDB;
CREATE TABLE Student ( id BIGINT UNSIGNED NOT NULL PRIMARY KEY, name VARCHAR(100) NOT NULL, INDEX Student_name (name) ) ENGINE = InnoDB;
@Entity
@Table
public class Student {
private long id;
private String name;
@Id
@GeneratedValue(strategy = GenerationType.TABLE,
generator = "studentGenerator")
@TableGenerator(name = "studentGenerator", table = "creatorkey",
pkColumnName = "TableName", pkColumnValue = "Publishers",
valueColumnName = "KeyValue", initialValue = 1,
allocationSize = 1)
@Column(name = "studentId")
public long getId() {
return id;
}name :主键生成策略定义的名字；table：生成器表在数据库中的名字；pkColumnName：生成器表的主键列的名字；pkColumnValue：生成器表主键列的值；valueColumnName：生成器表值列的名字；initialValue：生成器表初始值；allocationSize：生成器表数值递增或递减幅度。generator：主键生成策略定义的名字，该属性与name属性保持一致；generator = "studentGenerator"：使用生成器表的主键生成策略。 /**
* (Optional) The initial value to be used to initialize the column
* that stores the last value generated.
*/
int initialValue() default 0;
/**
* (Optional) The amount to increment by when allocating id
* numbers from the generator.
*/
int allocationSize() default 50;但是，根据实际测试结果，情况并非如源代码表示的那样。清空生成器表creatorkey、目标表student，去掉属性initialValue、allocationSize，执行持久化操作。 Student student = new Student();
student.setName("张三");
manager.persist(student);得到的结果却是这样的。
/**
* Defines a primary key generator that may be
* referenced by name when a generator element is specified for
* the {@link GeneratedValue} annotation. A table generator
* may be specified on the entity class or on the primary key
* field or property. The scope of the generator name is global
* to the persistence unit (across all generator types).@Entity
@Table
public class Book implements Serializable
{
private long id;
@Id
@GeneratedValue(strategy = GenerationType.TABLE,
generator = "studentGenerator")
public long getId()
{
return this.id;
}
public void setId(long id)
{
this.id = id;
}启动web server，报出如下异常。javax.persistence.PersistenceException: [PersistenceUnit: EntityMappings] Unable to build Hibernate SessionFactory Caused by: org.hibernate.AnnotationException: Unknown Id.generator: studentGenerator org.hibernate.AnnotationException: Unknown Id.generator: studentGenerator若在实体Book加上对主键生成策略的定义，就运行正常。
@Entity
@Table
public class Book implements Serializable
{
private long id;
@Id
@GeneratedValue(strategy = GenerationType.TABLE,
generator = "studentGenerator")
@TableGenerator(name = "studentGenerator", table = "creatorkey",
pkColumnName = "TableName", pkColumnValue = "Publishers",
valueColumnName = "KeyValue", initialValue = 1, allocationSize=1)
public long getId()
{
return this.id;
}
public void setId(long id)
{
this.id = id;
}标签：
原文地址：http://blog.csdn.net/seedshome/article/details/52239664
