在这段代码中，如何为组合键生成一个Java类(如何在hibernate中组合键):
create table Time (
levelStation int(15) not null,
src varchar(100) not null,
dst varchar(100) not null,
distance int(15) not null,
price int(15) not null,
confPathID int(15) not null,
constraint ConfPath_fk foreign key(confPathID) references ConfPath(confPathID),
primary key (levelStation, confPathID)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
当前回答
让我们举一个简单的例子。假设有两个表，分别叫test和customer，描述如下:
create table test(
test_id int(11) not null auto_increment,
primary key(test_id));
create table customer(
customer_id int(11) not null auto_increment,
name varchar(50) not null,
primary key(customer_id));
还有一个表用于跟踪测试和客户:
create table tests_purchased(
customer_id int(11) not null,
test_id int(11) not null,
created_date datetime not null,
primary key(customer_id, test_id));
我们可以看到，在表tests_bought中，主键是一个复合键，因此我们将使用<composite-id…>…</composite-id hbm.xml映射文件中的>标签。因此PurchasedTest.hbm.xml看起来像这样:
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="entities.PurchasedTest" table="tests_purchased">
<composite-id name="purchasedTestId">
<key-property name="testId" column="TEST_ID" />
<key-property name="customerId" column="CUSTOMER_ID" />
</composite-id>
<property name="purchaseDate" type="timestamp">
<column name="created_date" />
</property>
</class>
</hibernate-mapping>
但这并没有结束。在Hibernate中我们使用session。load (entityClass, id_type_object)使用主键查找并加载实体。在组合键的情况下，ID对象应该是一个单独的ID类(在上面的情况下是purchasedtestd类)，它只声明主键属性如下:
import java.io.Serializable;
public class PurchasedTestId implements Serializable {
private Long testId;
private Long customerId;
// an easy initializing constructor
public PurchasedTestId(Long testId, Long customerId) {
this.testId = testId;
this.customerId = customerId;
}
public Long getTestId() {
return testId;
}
public void setTestId(Long testId) {
this.testId = testId;
}
public Long getCustomerId() {
return customerId;
}
public void setCustomerId(Long customerId) {
this.customerId = customerId;
}
@Override
public boolean equals(Object arg0) {
if(arg0 == null) return false;
if(!(arg0 instanceof PurchasedTestId)) return false;
PurchasedTestId arg1 = (PurchasedTestId) arg0;
return (this.testId.longValue() == arg1.getTestId().longValue()) &&
(this.customerId.longValue() == arg1.getCustomerId().longValue());
}
@Override
public int hashCode() {
int hsCode;
hsCode = testId.hashCode();
hsCode = 19 * hsCode+ customerId.hashCode();
return hsCode;
}
}
重要的一点是，我们还实现了hashCode()和equals()两个函数，因为Hibernate依赖于它们。
其他回答
主键类必须定义equals和hashCode方法
When implementing equals you should use instanceof to allow comparing with subclasses. If Hibernate lazy loads a one to one or many to one relation, you will have a proxy for the class instead of the plain class. A proxy is a subclass. Comparing the class names would fail. More technically: You should follow the Liskows Substitution Principle and ignore symmetricity. The next pitfall is using something like name.equals(that.name) instead of name.equals(that.getName()). The first will fail, if that is a proxy.
http://www.laliluna.de/jpa-hibernate-guide/ch06s06.html
让我们举一个简单的例子。假设有两个表，分别叫test和customer，描述如下:
create table test(
test_id int(11) not null auto_increment,
primary key(test_id));
create table customer(
customer_id int(11) not null auto_increment,
name varchar(50) not null,
primary key(customer_id));
还有一个表用于跟踪测试和客户:
create table tests_purchased(
customer_id int(11) not null,
test_id int(11) not null,
created_date datetime not null,
primary key(customer_id, test_id));
我们可以看到，在表tests_bought中，主键是一个复合键，因此我们将使用<composite-id…>…</composite-id hbm.xml映射文件中的>标签。因此PurchasedTest.hbm.xml看起来像这样:
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="entities.PurchasedTest" table="tests_purchased">
<composite-id name="purchasedTestId">
<key-property name="testId" column="TEST_ID" />
<key-property name="customerId" column="CUSTOMER_ID" />
</composite-id>
<property name="purchaseDate" type="timestamp">
<column name="created_date" />
</property>
</class>
</hibernate-mapping>
但这并没有结束。在Hibernate中我们使用session。load (entityClass, id_type_object)使用主键查找并加载实体。在组合键的情况下，ID对象应该是一个单独的ID类(在上面的情况下是purchasedtestd类)，它只声明主键属性如下:
import java.io.Serializable;
public class PurchasedTestId implements Serializable {
private Long testId;
private Long customerId;
// an easy initializing constructor
public PurchasedTestId(Long testId, Long customerId) {
this.testId = testId;
this.customerId = customerId;
}
public Long getTestId() {
return testId;
}
public void setTestId(Long testId) {
this.testId = testId;
}
public Long getCustomerId() {
return customerId;
}
public void setCustomerId(Long customerId) {
this.customerId = customerId;
}
@Override
public boolean equals(Object arg0) {
if(arg0 == null) return false;
if(!(arg0 instanceof PurchasedTestId)) return false;
PurchasedTestId arg1 = (PurchasedTestId) arg0;
return (this.testId.longValue() == arg1.getTestId().longValue()) &&
(this.customerId.longValue() == arg1.getCustomerId().longValue());
}
@Override
public int hashCode() {
int hsCode;
hsCode = testId.hashCode();
hsCode = 19 * hsCode+ customerId.hashCode();
return hsCode;
}
}
重要的一点是，我们还实现了hashCode()和equals()两个函数，因为Hibernate依赖于它们。
你需要使用@EmbeddedId:
@Entity
class Time {
@EmbeddedId
TimeId id;
String src;
String dst;
Integer distance;
Integer price;
}
@Embeddable
class TimeId implements Serializable {
Integer levelStation;
Integer confPathID;
}
看来你是从零开始的。尝试使用可用的逆向工程工具，如Netbeans Entities from Database，至少实现基本的自动化(如嵌入式id)。如果你有很多桌子，这可能会成为一个非常令人头痛的问题。我建议避免重新发明轮子，并使用尽可能多的可用工具，将编码减少到最小和最重要的部分，即您想要做的部分。
另一种选择是将is映射为ConfPath表中复合元素的map。
不过，这种映射将受益于(ConfPathID,levelStation)上的索引。
public class ConfPath {
private Map<Long,Time> timeForLevelStation = new HashMap<Long,Time>();
public Time getTime(long levelStation) {
return timeForLevelStation.get(levelStation);
}
public void putTime(long levelStation, Time newValue) {
timeForLevelStation.put(levelStation, newValue);
}
}
public class Time {
String src;
String dst;
long distance;
long price;
public long getDistance() {
return distance;
}
public void setDistance(long distance) {
this.distance = distance;
}
public String getDst() {
return dst;
}
public void setDst(String dst) {
this.dst = dst;
}
public long getPrice() {
return price;
}
public void setPrice(long price) {
this.price = price;
}
public String getSrc() {
return src;
}
public void setSrc(String src) {
this.src = src;
}
}
映射:
<class name="ConfPath" table="ConfPath">
<id column="ID" name="id">
<generator class="native"/>
</id>
<map cascade="all-delete-orphan" name="values" table="example"
lazy="extra">
<key column="ConfPathID"/>
<map-key type="long" column="levelStation"/>
<composite-element class="Time">
<property name="src" column="src" type="string" length="100"/>
<property name="dst" column="dst" type="string" length="100"/>
<property name="distance" column="distance"/>
<property name="price" column="price"/>
</composite-element>
</map>
</class>
