Java Tutorial/JPA/Primary Key
Содержание
Define Extra Class For Compound Key
File: Employee.java
<source lang="java">
import javax.persistence.Entity; import javax.persistence.Id; import javax.persistence.IdClass; @Entity @IdClass(EmployeePK.class) public class Employee implements java.io.Serializable {
private String firstName;
@Id
private String lastName;
@Id
private long ssn;
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
public long getSsn() {
return ssn;
}
public void setSsn(long ssn) {
this.ssn = ssn;
}
} class EmployeePK implements java.io.Serializable {
private String lastName;
private long ssn;
public EmployeePK() {
}
public EmployeePK(String lastName, long ssn) {
this.lastName = lastName;
this.ssn = ssn;
}
public String getLastName() {
return this.lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
public long getSsn() {
return ssn;
}
public void setSsn(long ssn) {
this.ssn = ssn;
}
public boolean equals(Object obj) {
if (obj == this)
return true;
if (!(obj instanceof EmployeePK))
return false;
EmployeePK pk = (EmployeePK) obj;
if (!lastName.equals(pk.lastName))
return false;
if (ssn != pk.ssn)
return false;
return true;
}
public int hashCode() {
return lastName.hashCode() + (int) ssn;
}
}</source>
Embedded Compound Primary Key
File: Student.java
<source lang="java">
import javax.persistence.Column; import javax.persistence.Embeddable; import javax.persistence.EmbeddedId; import javax.persistence.Entity; @Entity public class Student implements java.io.Serializable {
@EmbeddedId private StudentId id; private String name;
public Student() {}
public Student(String country, int id) {
this.id = new StudentId(country, id);
}
public int getId() {
return id.getId();
}
public String getCountry() {
return id.getCountry();
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String toString() {
return "Student id: " + getId() + " name: " + getName() + " country: " + getCountry();
}
} @Embeddable class StudentId implements java.io.Serializable{
private String country;
@Column(name="Student_ID")
private int id;
public StudentId() {}
public StudentId(String country, int id) {
this.country = country;
this.id = id;
}
public String getCountry() { return country; }
public int getId() { return id; }
public boolean equals(Object o) {
return ((o instanceof StudentId) &&
country.equals(((StudentId)o).getCountry()) &&
id == ((StudentId) o).getId());
}
public int hashCode() {
return country.hashCode() + id;
}
}</source>
Id Containing Relationship
File: Helper.java
<source lang="java">
import java.sql.Connection; import java.sql.DriverManager; import java.sql.ResultSet; import java.sql.ResultSetMetaData; import java.sql.Statement; public class Helper {
public static void checkData() throws Exception {
Class.forName("org.hsqldb.jdbcDriver");
Connection conn = DriverManager.getConnection("jdbc:hsqldb:data/tutorial", "sa", "");
Statement st = conn.createStatement();
ResultSet mrs = conn.getMetaData().getTables(null, null, null, new String[] { "TABLE" });
while (mrs.next()) {
String tableName = mrs.getString(3);
System.out.println("\n\n\n\nTable Name: "+ tableName);
ResultSet rs = st.executeQuery("select * from " + tableName);
ResultSetMetaData metadata = rs.getMetaData();
while (rs.next()) {
System.out.println(" Row:");
for (int i = 0; i < metadata.getColumnCount(); i++) {
System.out.println(" Column Name: "+ metadata.getColumnLabel(i + 1)+ ", ");
System.out.println(" Column Type: "+ metadata.getColumnTypeName(i + 1)+ ": ");
Object value = rs.getObject(i + 1);
System.out.println(" Column Value: "+value+"\n");
}
}
}
}
}</source>
ID Entity With Hash Code And Equals
File: Main.java
<source lang="java">
import javax.persistence.EntityManager; import javax.persistence.EntityManagerFactory; import javax.persistence.Persistence; import javax.persistence.Query; public class Main {
static EntityManagerFactory emf = Persistence.createEntityManagerFactory("JPAService");
static EntityManager em = emf.createEntityManager();
public static void main(String[] a) throws Exception {
em.getTransaction().begin();
em.getTransaction().rumit(); em.close(); emf.close(); Helper.checkData(); }
}</source>
Not Nullable ID
File: Student.java
<source lang="java">
import javax.persistence.Column; import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.GenerationType; import javax.persistence.Id; @Entity public class Student {
@Id @Column(name = "ID", nullable = false) private int id; transient private String name;
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 String toString() {
return "\n\nID:" + id + "\nName:" + name + "\n\n";
}
}</source>
Set ID By Yourself
File: Gender.java
<source lang="java">
public enum Gender {
MALE, FEMALE
}</source>
Set Primary Key Join Column For Entities In Hierarchy
File: Person.java
<source lang="java">
import javax.persistence.DiscriminatorValue; import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.Id; import javax.persistence.Inheritance; import javax.persistence.InheritanceType; import javax.persistence.PrimaryKeyJoinColumn; @Entity @Inheritance(strategy = InheritanceType.JOINED) public class Person implements java.io.Serializable {
private int id;
private String firstName;
private String lastName;
@Id
@GeneratedValue
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getFirstName() {
return firstName;
}
public void setFirstName(String first) {
this.firstName = first;
}
public String getLastName() {
return lastName;
}
public void setLastName(String last) {
this.lastName = last;
}
} @Entity @DiscriminatorValue("CUST") class Customer extends Person {
private String street;
private String city;
private String state;
private String zip;
public String getStreet() {
return street;
}
public void setStreet(String street) {
this.street = street;
}
public String getCity() {
return city;
}
public void setCity(String city) {
this.city = city;
}
public String getState() {
return state;
}
public void setState(String state) {
this.state = state;
}
public String getZip() {
return zip;
}
public void setZip(String zip) {
this.zip = zip;
}
} @Entity @PrimaryKeyJoinColumn(name = "EMP_PK") class Employee extends Customer {
private int employeeId;
public int getEmployeeId() {
return employeeId;
}
public void setEmployeeId(int id) {
employeeId = id;
}
}</source>
Use Current Milisecond As ID
File: Student.java
<source lang="java">
import java.util.Date; import javax.persistence.Basic; import javax.persistence.Entity; import javax.persistence.Id; @Entity public class Student {
@Id
private long id = System.currentTimeMillis();
@Basic
private String name;
@Basic
private Date dateOfBirth = new Date();
public Date getDateOfBirth() {
return dateOfBirth;
}
public void setDateOfBirth(Date dateOfBirth) {
this.dateOfBirth = dateOfBirth;
}
public long getId() {
return id;
}
public void setId(long id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}</source>
Use UUID As Primary Key
File: Student.java
<source lang="java">
import javax.persistence.Basic; import javax.persistence.Column; import javax.persistence.Entity; import javax.persistence.FetchType; import javax.persistence.Id; import javax.persistence.Lob; @Entity public class Student {
@Id private String id; private String name;
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String toString() {
return "\n\nID:" + id + "\nName:" + name + "\n\n";
}
}</source>
