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
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>
其他回答
使用hbm.xml
<composite-id>
<!--<key-many-to-one name="productId" class="databaselayer.users.UserDB" column="user_name"/>-->
<key-property name="productId" column="PRODUCT_Product_ID" type="int"/>
<key-property name="categoryId" column="categories_id" type="int" />
</composite-id>
使用注释
复合键类
public class PK implements Serializable{
private int PRODUCT_Product_ID ;
private int categories_id ;
public PK(int productId, int categoryId) {
this.PRODUCT_Product_ID = productId;
this.categories_id = categoryId;
}
public int getPRODUCT_Product_ID() {
return PRODUCT_Product_ID;
}
public void setPRODUCT_Product_ID(int PRODUCT_Product_ID) {
this.PRODUCT_Product_ID = PRODUCT_Product_ID;
}
public int getCategories_id() {
return categories_id;
}
public void setCategories_id(int categories_id) {
this.categories_id = categories_id;
}
private PK() { }
@Override
public boolean equals(Object o) {
if ( this == o ) {
return true;
}
if ( o == null || getClass() != o.getClass() ) {
return false;
}
PK pk = (PK) o;
return Objects.equals(PRODUCT_Product_ID, pk.PRODUCT_Product_ID ) &&
Objects.equals(categories_id, pk.categories_id );
}
@Override
public int hashCode() {
return Objects.hash(PRODUCT_Product_ID, categories_id );
}
}
实体类
@Entity(name = "product_category")
@IdClass( PK.class )
public class ProductCategory implements Serializable {
@Id
private int PRODUCT_Product_ID ;
@Id
private int categories_id ;
public ProductCategory(int productId, int categoryId) {
this.PRODUCT_Product_ID = productId ;
this.categories_id = categoryId;
}
public ProductCategory() { }
public int getPRODUCT_Product_ID() {
return PRODUCT_Product_ID;
}
public void setPRODUCT_Product_ID(int PRODUCT_Product_ID) {
this.PRODUCT_Product_ID = PRODUCT_Product_ID;
}
public int getCategories_id() {
return categories_id;
}
public void setCategories_id(int categories_id) {
this.categories_id = categories_id;
}
public void setId(PK id) {
this.PRODUCT_Product_ID = id.getPRODUCT_Product_ID();
this.categories_id = id.getCategories_id();
}
public PK getId() {
return new PK(
PRODUCT_Product_ID,
categories_id
);
}
}
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;
}
假设你有以下数据库表:
首先，你需要创建包含复合标识符的@Embeddable:
@Embeddable
public class EmployeeId implements Serializable {
@Column(name = "company_id")
private Long companyId;
@Column(name = "employee_number")
private Long employeeNumber;
public EmployeeId() {
}
public EmployeeId(Long companyId, Long employeeId) {
this.companyId = companyId;
this.employeeNumber = employeeId;
}
public Long getCompanyId() {
return companyId;
}
public Long getEmployeeNumber() {
return employeeNumber;
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (!(o instanceof EmployeeId)) return false;
EmployeeId that = (EmployeeId) o;
return Objects.equals(getCompanyId(), that.getCompanyId()) &&
Objects.equals(getEmployeeNumber(), that.getEmployeeNumber());
}
@Override
public int hashCode() {
return Objects.hash(getCompanyId(), getEmployeeNumber());
}
}
有了这些，我们可以映射使用复合标识符的Employee实体，方法是用@EmbeddedId注释它:
@Entity(name = "Employee")
@Table(name = "employee")
public class Employee {
@EmbeddedId
private EmployeeId id;
private String name;
public EmployeeId getId() {
return id;
}
public void setId(EmployeeId id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
Phone实体与Employee有@ManyToOne关联，需要通过两个@JoinColumnmappings从父类引用复合标识符:
@Entity(name = "Phone")
@Table(name = "phone")
public class Phone {
@Id
@Column(name = "`number`")
private String number;
@ManyToOne
@JoinColumns({
@JoinColumn(
name = "company_id",
referencedColumnName = "company_id"),
@JoinColumn(
name = "employee_number",
referencedColumnName = "employee_number")
})
private Employee employee;
public Employee getEmployee() {
return employee;
}
public void setEmployee(Employee employee) {
this.employee = employee;
}
public String getNumber() {
return number;
}
public void setNumber(String number) {
this.number = number;
}
}
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>
