我在 DB2 DB 上调优了 Eclipselink 持久性提供程序。下面列出了简化定义的 3 个表格:
CREATE TABLE root
(
id CHAR(32) NOT NULL PRIMARY KEY,
rec_type VARCHAR(20)
);
CREATE TABLE derived
(
id CHAR(32) NOT NULL PRIMARY KEY,
...
);
ALTER TABLE derived ADD CONSTRAINT fk_derived_to_root FOREIGN KEY (id) REFERENCES root(id);
CREATE TABLE secondary
(
derived_id NOT NULL PRIMARY KEY,
...
);
ALTER TABLE secondary ADD CONSTRAINT fk_secondary_to_derived FOREIGN KEY (derived_id) REFERENCES derived(id);
下面列出了这些实体的 Java 实体类,根实体:
@javax.persistence.Table(name = "ROOT")
@Entity
@DiscriminatorColumn(name = "REC_TYPE")
@Inheritance(strategy = InheritanceType.JOINED)
public class RootEntity {
private String id;
@javax.persistence.Column(name = "ID")
@Id
@GeneratedValue(generator = "system-uuid")
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
private String principalType;
@Column(name = "PRINCIPAL_TYPE")
public String getPrincipalType() {
return principalType;
}
public void setPrincipalType(String principalType) {
this.principalType = principalType;
}
...
}
派生实体:
@javax.persistence.Table(name = "DERIVED")
@Entity
@DescriminatorValue("DERIVED")
public class DerivedEntity extends RootEntity {
private SecondaryEntity secondaryEntity;
@OneToOne(mappedBy = "derived_id")
public SecondaryEntity getSecondaryEntity() {
return secondaryEntity;
}
public void setSecondaryEntity(SecondaryEntity secondaryEntity) {
this.secondaryEntity = secondaryEntity;
}
...
}
我在测试日志中没有看到派生表插入:
--INSERT INTO ROOT (ID, REC_TYPE) VALUES (?, ?)
bind => [241153d01c204ed79109ce658c066f4c, Derived]
--INSERT INTO SECONDARY (DERIVED_ID, ...) VALUES (?, ...)
bind => [241153d01c204ed79109ce658c066f4c, ...]
Exception [EclipseLink-4002] (Eclipse Persistence Services - 2.3.2.v20111125-r10461): org.eclipse.persistence.exceptions.DatabaseException
Internal Exception: com.ibm.db2.jcc.am.fo: DB2 SQL Error: SQLCODE=-530, SQLSTATE=23503, SQLERRMC=SCHEM.SECONDARY.FK_SECONDARY_TO_DERIVED, DRIVER=3.57.82
所以问题是:为什么Eclipselink在插入到表中之前不将新记录插入DERIVED
表中SECONDARY
?
附言当没有SECONDARY
表(仅限ROOT
和DERIVED
表)或未使用继承(DERIVED
表生成id)时,一切正常。
对于继承,JPA 假定相关表中的外键约束引用根表。
您可以更改约束以引用根表,或者,
使用描述符定制器设置,
descriptor.setHasMultipleTableConstraintDependecy(true);
或
定制 OneToOneMapping 以使其外键引用辅助表(JPA 注释始终使其引用根表)。
但是,请记录一个错误,因为 JPA 连接列应该允许您定义辅助表的外键。
EclipseLink 将插入延迟到辅助表中的原因是允许按表对插入进行分组,以允许批量写入并避免数据库死锁。