Hibernate - POJO and HBM file creation best practice

Middlegen-Hibernate和hibernate-extensions生成hbm映射文件和POJO

hibernate:pojo

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Refactoring Enum --> POJO using Hibernate Persistence

Having faced this problem (mentioned in my earlier post) in the code that we inherited, I set out to refactor an Enum to a POJO. We are using Hibernate as our ORM. Here is our Enum ProcessStatus:

public enum ProcessStatus {
  RUNNING, WAITING, COMPLETE;
}

Here is the Process mapped to PROCESS table using Hibernate.

@Entity (name = "PROCESS")
public class Process {
  private ProcessStatus status;
  ...
  public void setStatus(ProcessStatus status) {
    this.status = status;
  }
  @Enumerated(value = EnumType.STRING)
  public ProcessStatus getStatus() {
    return status;
  }
  ...
}

and Let us take a client Action (called from UI layer) that uses this Enum. Assume that all the dependencies get injected when the action class is instantiated by the container (use Spring)

public class ProcessAction extends Action {
  private Process process; 
  private String status;
  private DataRepository dataRepository;
  ...
  public void setDataRepository(DataRepository dataRepository) {
    this.dataRepository = dataRepository;
  } 
  public void setStatus(String status) {
    this.status = status;
  }
  public String updateProcessStatus() {
    if (isInvalid(status)) {
      return ERROR;
    }
    process.setStatus(ProcessStatus.valueOf(status));
    dataRepository.update(process);
    return SUCCESS;
  }
  private boolean isInvalid(String status) {
    if (status == null || "".equals(status)) {
      return false;
    }
    for (ProcessStatus processStatus : ProcessStatus.values()) {
      if (processStatus.name().equalsIgnoreCase(status))
        return true;
    }
    return false;      
  }
}

Here is the DataRepository code that talks to the underlying database and issues Hibernate queries. Ideally, this should be an interface so as to facilitate unit testing with Mock objects, but for now lets take it as a concrete class)

public class DataRepository {
  private SessionFactory sessionFactory;
  ...
  private Session getSession() {
    return HibernateUtils.getSession(sessionFactory);
  }
  public void update(Object object) {
     getSession().saveOrUpdate(object);
  }
  public <T> List<T> findAll(Class<T> clazz) {
    return getSession().createCriteria(clazz).list();
  }
  ...
}

1. As Enums are constants, there could be direct references to them or references to static methods that all Enums have: valueOf(String name), values() etc... References to name(), and ordinal() can as well exist in the code. Introduce a value and a name field in the Enum and the private Constructor. Give value field the same value as what ordinal() would return for that Enum constant.

   public enum ProcessStatus {
     RUNNING(0, "RUNNING"), 
     WAITING(1, "WAITING"), 
     COMPLETE(2, "COMPLETE");
   
     private String name;
     private Integer value;
   
     private ProcessStatus(Integer value, String name) {
       this.value = value;
       this.name = name;
     }
     public Integer getValue() {
       return value;
     }
     public String getName() {
       return name;
     }
   }
   

2. Change all references in the code to the name method to getName() method and ordinal() to getValue() method. The getValue() method returns the value that ordinal() used to return earlier and the getName() method returns the name of the Enum constants.

   public class ProcessAction extends Action {
     private Process process;
     private String status;
     private DataRepository dataRepository;
     ...
     public void setDataRepository(DataRepository dataRepository) {
       this.dataRepository = dataRepository;
     } 
     public void setStatus(String status) {
       this.status = status;
     }
     public String updateProcessStatus() {
       if (isInvalid(status)) {
         return ERROR;
       }
       process.setStatus(ProcessStatus.valueOf(status));
       dataRepository.update(process);
       return SUCCESS;
     }
     private boolean isInvalid(String status) {
       if (status == null || "".equals(status)) {
         return false;
       }
       for (ProcessStatus processStatus : ProcessStatus.values()) {
         if (processStatus.          name()          getName().equalsIgnoreCase(status))
           return true;
       }
       return false;      
     }
   }
   

3. Convert Enum to a Regular Java Class and provide implementations of values() and valueOf() etc... and the compareTo() methods. Override hashCode() and equals() methods as well.

   public class ProcessStatus implements Comparable<ProcessStatus> {
               RUNNING(0, "RUNNING"), 
               WAITING(1, "WAITING"), 
               COMPLETE(2, "COMPLETE");          
     public static final ProcessStatus RUNNING = new ProcessStatus(0, "RUNNING");
     public static final ProcessStatus WAITING = new ProcessStatus(1, "WAITING");
     public static final ProcessStatus COMPLETE = new ProcessStatus(2, "COMPLETE");
     private static ProcessStatus [] ALL = new ProcessStatus [] { RUNNING, WAITING, COMPLETE };
     
     private String name;
     private Integer value;
   
     private ProcessStatus(Integer value, String name) {
       this.value = value;
       this.name = name;
     }
     public Integer getValue() {
       return value;
     }
     public String getName() {
       return name;
     }
     public static ProcessStatus valueOf(String statusName) {
       for (ProcessStatus processStatus : ALL) {
          if (processStatus.getName().equals(statusName))
             return processStatus;
       }
       return null;
     }
     public ProcessStatus[] values() {
        return ALL;
     }
     public int compareTo(ProcessStatus other) {
       return this.value.compareTo(other.value);
     }
     public int hashCode() { ... }
     public boolean equals(Object object) { ... }
   }
   

   Run the Unit and Acceptance Tests to get a Green (assuming you are using JUnit and FIT automated testing frameworks for Unit and Acceptance tests).

4. Next is to create a table PROCESSTATUS containing three columns id (auto-increment/sequence), name, value. Populate the table with the name and value (same as ProcessStatus constants).

   +---+----------+-------+
   |id | name     | value |
   +---+----------+-------+
   | 1 | RUNNING  | 0     |
   | 2 | WAITING  | 1     |
   | 3 | COMPLETE | 2     |
   +---+----------+-------+
   

5. Then, map ProcessStatus class to the newly created PROCESSTATUS table. We want this class to be immutable and hence we will make the fields non-updatable and new statuses are added from the backend. Add another Id field as primary key and the corresponding getter.

             @Entity (name = "PROCESSSTATUS")
   public class ProcessStatus implements Comparable<ProcessStatus> {
     public static final ProcessStatus RUNNING = new ProcessStatus(0, "RUNNING");
     public static final ProcessStatus WAITING = new ProcessStatus(1, "WAITING");
     public static final ProcessStatus COMPLETE = new ProcessStatus(2, "COMPLETE");
     private static ProcessStatus [] ALL = new ProcessStatus [] { RUNNING, WAITING, COMPLETE };
               
     @Id
     @GeneratedValue(strategy = GenerationType.AUTO)
     private Long id;
     @Column (updatable = false, insertable = false)
     private String name;
               @Column (updatable = false, insertable = false)
     private Integer value;
   
     private ProcessStatus(Integer value, String name) {
       this.value = value;
       this.name = name;
     }          
     public Long getId() {
       return Id;
     }
     public Integer getValue() {
       return value;
     }
     public String getName() {
       return name;
     }
     public static ProcessStatus valueOf(String statusName) {
       for (ProcessStatus processStatus : ALL) {
          if (processStatus.getName().equals(statusName))
             return processStatus;
       }
       return null;
     }
     public ProcessStatus[] values() {
        return ALL;
     }
     ...
   }
   

   Update all the String references in the PROCESS table to Id references of PROCESSSTATUS table. The Process class will change as:

   @Entity (name = "PROCESS")
   public class Process {
     private ProcessStatus status;
     ...
     public void setStatus(ProcessStatus status) {
       this.status = status;
     }
               @Enumerated(value = EnumType.STRING)
               @ManyToOne
     @JoinColumn (name = "status")
     public ProcessStatus getStatus() {
       return status;
     }
     ...
   }
   

6. Now, we need to move away from the static method references in the Client classes and get rid of values() and valueOf() methods... ProcessAction is one such class that uses these methods. We replace them with calls to methods in DataRepository class. Introduce findProcessStatusByName() method in DataRepository to replace all client calls to valueOf() method. All client calls to values() method will be replaced by findAll() method in DataRepository.

   public class DataRepository {
     private SessionFactory sessionFactory;
     ...
     private Session getSession() {
       return HibernateUtils.getSession(sessionFactory);
     }
     public void update(Object object) {
        getSession().saveOrUpdate(object);
     }
     public <T> List<T> findAll(Class<T> clazz) {
       return getSession().createCriteria(clazz).list();
     }          
     public ProcessStatus findProcessStatusByName(String name) {
       return (ProcessStatus)getSession().createCriteria(ProcessStatus.class)
                            .add(Restrictions.eq("name", name))
                            .uniqueResult();
     }
     ...
   }
   

   Here is the changed ProcessAction class

   public class ProcessAction extends Action {
     private Process process; 
     private String status;
     private DataRepository dataRepository;
     ...
     public void setDataRepository(DataRepository dataRepository) {
       this.dataRepository = dataRepository;
     } 
     public void setStatus(String status) {
       this.status = status;
     }
     public String updateProcessStatus() {
       if (isInvalid(status)) {
         return ERROR;
       }
                 ProcessStatus processStatus = ProcessStatus.valueOf(status); 
                 ProcessStatus processStatus = dataRepository.findProcessStatusByName(status);
       process.setStatus(processStatus);
       dataRepository.update(process);
       return SUCCESS;
     }
     private boolean isInvalid(String status) {
       if (status == null || "".equals(status)) {
         return false;
       }
                 for (ProcessStatus processStatus : ProcessStatus.values()) {          
       List<ProcessStatus> allStatuses = dataRepository.findAll(ProcessStatus.class);
       for (ProcessStatus processStatus : allStatuses) {
         if (processStatus.getName().equalsIgnoreCase(status))
           return true;
       }
       return false;      
     }
   }
   

   Finally, we need to remove all the references to the Enum constants, if any and replace them with calls to dataRepository.findProcessStatusByName(). Delete all the Enum constant values, values() and valuesOf() methods. We no longer need the private constructor as well. The cleaned up ProcessStatus POJO would then look like:

             @Entity (name = "PROCESSSTATUS")
   public class ProcessStatus implements Comparable<ProcessStatus> {
     @Id
     @GeneratedValue(strategy = GenerationType.AUTO)
     private Long id;
     @Column (updatable = false, insertable = false)
     private String name;
     @Column (updatable = false, insertable = false)
     private Integer value;
   
     public Long getId() {
       return Id;
     }
     public Integer getValue() {
       return value;
     }
     public String getName() {
       return name;
     }
     public int compareTo(ProcessStatus other) {
       return this.value.compareTo(other.value);
     }
     public int hashCode() { ... }
     public boolean equals(Object object) { ... }
   }
   

   Thats all, this completes this little involved refactoring.

Re-run the test suite and get the Green bar!