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JPA 教程 - JPA 字段映射示例

当将 Java bean 字段映射到数据库列时，我们可以选择标记字段，标记 getter 方法并标记两者。

标记字段

以下代码来自 Professor.java。

它显示如何将主键列标记为 Java bean 字段标识。

package cn.w3cschool.common;
import javax.persistence.Entity;
import javax.persistence.Id;@Entity
public class Professor {@Idprivate int id;private String name;private long salary;public int getId() {return id;}public void setId(int id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public long getSalary() {return salary;}public void setSalary(long salary) {this.salary = salary;}public String toString() {return "Employee id: " + getId() + " name: " + getName() + " salary: " + getSalary();}
}

下面的代码来自 PersonDaoImpl.java。

package cn.w3cschool.common;import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;import org.springframework.transaction.annotation.Transactional;@Transactional
public class PersonDaoImpl {public void test() {Professor emp = new Professor();emp.setId(1);emp.setName("name");emp.setSalary(12345);em.persist(emp);}@PersistenceContextprivate EntityManager em;
}

下载 Access_Field.zip

这里是运行代码后的数据库转储。

Table Name: PROFESSORRow:Column Name: ID,Column Type: INTEGER:Column Value: 1Column Name: NAME,Column Type: VARCHAR:Column Value: nameColumn Name: SALARY,Column Type: BIGINT:Column Value: 12345

标记属性 getter 方法

以下代码来自 Professor.java。

用于标记要用作数据库表主键列的字段的 @Id 注释将添加到 getter 方法。

package cn.w3cschool.common;
import javax.persistence.Entity;
import javax.persistence.Id;@Entity
public class Professor {private int id;private String name;private long wage;@Idpublic int getId() {return id;}public void setId(int id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public long getSalary() {return wage;}public void setSalary(long salary) {this.wage = salary;}public String toString() {return "Employee id: " + getId() + " name: " + getName() + " salary: " + getSalary();}
}

下载 Access_Property.zip

以下是在运行上面的代码后的数据库转储。

Table Name: PROFESSORRow:Column Name: ID,Column Type: INTEGER:Column Value: 1Column Name: NAME,Column Type: VARCHAR:Column Value: nameColumn Name: SALARY,Column Type: BIGINT:Column Value: 12345

混合标记

使用 JPA，我们可以标记字段和 getter 方法。

以下代码来自 Professor.java。

package cn.w3cschool.common;import javax.persistence.Access;
import javax.persistence.AccessType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Transient;@Access(AccessType.FIELD)
@Entity
public class Professor {public static String LOCAL_AREA_CODE = "999";@Idprivate int id;@Transientprivate String phoneNum;public int getId() {return id;}public void setId(int id) {this.id = id;}public String getPhoneNumber() {return phoneNum;}public void setPhoneNumber(String num) {this.phoneNum = num;}@Access(AccessType.PROPERTY)@Column(name = "PHONE")protected String getPhoneNumberForDb() {if (null != phoneNum && phoneNum.length() == 10)return phoneNum;elsereturn LOCAL_AREA_CODE + phoneNum;}protected void setPhoneNumberForDb(String num) {if (num.startsWith(LOCAL_AREA_CODE))phoneNum = num.substring(3);elsephoneNum = num;}
}

下面的代码来自 PersonDaoImpl.java。

package cn.w3cschool.common;import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;import org.springframework.transaction.annotation.Transactional;@Transactional
public class PersonDaoImpl {public void test() {Professor emp = new Professor();emp.setId(1);emp.setPhoneNumber("123456789");em.persist(emp);}@PersistenceContextprivate EntityManager em;
}

下载 Access_Mixed.zip

Table Name: PROFESSORRow:Column Name: ID,Column Type: INTEGER:Column Value: 1Column Name: PHONE,Column Type: VARCHAR:Column Value: 999123456789