Mapping boolean field to Database In open Jpa

[b]今天研究Open Jpa的文档时发现 它的 @PrePersist @PostPersist @PostLoan这些Callback 方法 非常有用，让我们可以在entity persist 或者 load 前后做一些我们的处理,比如它解决常见的boolean field 不能跟DB 里field Mapping 的问题（Oracle and DB2 没有相应的boolean field Type）。

注意因为displayFlag是一个页面显示字段，我们是用deleteFlag来跟db里的DELETE_FLAG来mapping ,所以我们要给displayFlag加上@Transient声明，不让它成为一个可persist的field,要不然运行时会抛exception.


Example Code 如下[/b]

@Entity

@NamedQueries({
	@NamedQuery(name="magsOverPrice",
	query="SELECT x FROM Magazine x WHERE x.price > ?1"),
	@NamedQuery(name="magsByTitle",
	query="SELECT x FROM Magazine x WHERE x.title = :titleParam")
	})
@EntityListeners({MagazineListener.class})
@IdClass(Magazine.MagazineId.class)
@Table(name="MAGAZINE")
public class Magazine {
	@Id private String isbn;
	@Id private String title;
	@Column(name="PRICE")
   private BigDecimal price;
   @Column(name="SOLDCOPY")
   private int copySold;
   @Column(name="VERS")
   private int version;
   @Column(name="DELETE_FLG")
   private String deleteFlag;

   @Transient
   private boolean displayFlag;


   public static class MagazineId {
	   private String isbn;
	   private String title;


	@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result + ((isbn == null) ? 0 : isbn.hashCode());
		result = prime * result + ((title == null) ? 0 : title.hashCode());
		return result;
	}
	@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if (obj == null)
			return false;
		if (getClass() != obj.getClass())
			return false;
		final MagazineId other = (MagazineId) obj;
		if (isbn == null) {
			if (other.isbn != null)
				return false;
		} else if (!isbn.equals(other.isbn))
			return false;
		if (title == null) {
			if (other.title != null)
				return false;
		} else if (!title.equals(other.title))
			return false;
		return true;
	}




	public MagazineId() {

	}
	public String getIsbn() {
		return isbn;
	}
	public void setIsbn(String isbn) {
		this.isbn = isbn;
	}
	public String getTitle() {
		return title;
	}
	public void setTitle(String title) {
		this.title = title;
	}

  }

	@PrePersist
	private void covertDisplayToDB() {
		if (this.displayFlag) {
			this.deleteFlag = "Y";
		}else {
			this.deleteFlag = "N";
		}
	}

	@PostLoad
	private void covertDBValueToDisplay() {
		if (this.deleteFlag != null && !this.deleteFlag.equals("") && this.deleteFlag.equals("Y")) {
			this.displayFlag = true;
		}else {
			this.displayFlag = false;
		}
	} 
public String getIsbn() {
	return isbn;
}
public void setIsbn(String isbn) {
	this.isbn = isbn;
}
public String getTitle() {
	return title;
}
public void setTitle(String title) {
	this.title = title;
}
public BigDecimal getPrice() {
	return price;
}
public void setPrice(BigDecimal price) {
	this.price = price;
}
public int getCopySold() {
	return copySold;
}
public void setCopySold(int copySold) {
	this.copySold = copySold;
}
public int getVersion() {
	return version;
}
public void setVersion(int version) {
	this.version = version;
}
public Magazine() {
	super();
}


public String getDeleteFlag() {
	return deleteFlag;
}
public void setDeleteFlag(String deleteFlag) {
	this.deleteFlag = deleteFlag;
}
public boolean isDisplayFlag() {
	return displayFlag;
}
public void setDisplayFlag(boolean displayFlag) {
	this.displayFlag = displayFlag;
}
@Override
public int hashCode() {
	final int prime = 31;
	int result = 1;
	result = prime * result + ((isbn == null) ? 0 : isbn.hashCode());
	result = prime * result + ((title == null) ? 0 : title.hashCode());
	return result;
}
@Override
public boolean equals(Object obj) {
	if (this == obj)
		return true;
	if (obj == null)
		return false;
	if (getClass() != obj.getClass())
		return false;
	final Magazine other = (Magazine) obj;
	if (isbn == null) {
		if (other.isbn != null)
			return false;
	} else if (!isbn.equals(other.isbn))
		return false;
	if (title == null) {
		if (other.title != null)
			return false;
	} else if (!title.equals(other.title))
		return false;
	return true;
}


}

[b]这个class 里的covertDisplayToDB 方法 用来在Magazine persist 前把页面displayFlag(boolean) 转换成DB存储的field类型 varchar.

covertDBValueToDisplay 方法用来把从DB抓出来的varchar类型的deleteFlag 转换成页面显示的dsiplayFlag.


当然我们也可以给这个entity class加上一个listener,然后把所有的Annotation的方法放在listener里。

Example Code 如下 首先给entity加上EntityListener Annotation @EntityListeners({MagazineListener.class}) 然后把我们的prePersist 跟PostLoad 的Annotation 方法移到listener中[/b]

public class MagazineListener {
	private static final Logger log = Logger.getLogger(MagazineListener.class);




	@PrePersist
	private void covertDisplayToDB(Object persistObject) {
		Magazine magazine = (Magazine) persistObject;
		if (magazine.isDisplayFlag()) {
			magazine.setDeleteFlag("Y");
		}else {
			magazine.setDeleteFlag("N");
		}
	}

	@PostLoad
	private void covertDBValueToDisplay(Object persistObject) {
		Magazine magazine = (Magazine) persistObject;
		if (magazine != null && magazine.getDeleteFlag() != null && !magazine.getDeleteFlag().equals("") && magazine.getDeleteFlag().equals("Y")) {
			magazine.setDisplayFlag(true);
		}else {
			magazine.setDisplayFlag(false);
		}
	} 



	}