Hibernate – One-to-one relationship example

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Hibernate – One-to-one relationship example

февруари 5th, 2010

admin

A one-to-one relationships occurs when one entity is related to exactly one occurrence in another entity.

“One-to-one” example

This is a one-to-one relationship table design, a STOCK table contains exactly one record in STOCK_DETAIL table. Both tables have the same Stock_Id as primary key. In STOCK_DETAIL table, Stock_Id is the primary key and also a foreign key to STOCK table. This is one of the common ways to define one-to-one relationship. More detail…

Hibernate implementation

In Hibernate, this “one-to-one” relationship can implemented in two ways :

Hibernate XML Mapping file
Hibernate Annotation

1. Hibernate XML mapping file

In XML mapping way, you need two Java classes to hold the table data.

Stock.java -> STOCK table
StockDetail.java -> STOCK_DETAIL table

and two XML mapping files to describe the table relationship.

Stock.hbm.xml -> STOCK table
StockDetail.hbm.xml -> STOCK_DETAIL table

Stock.java

...
public class Stock implements java.io.Serializable {
	private StockDetail stockDetail;
	...
	public StockDetail getStockDetail() {
		return this.stockDetail;
	}
	public void setStockDetail(StockDetail stockDetail) {
		this.stockDetail = stockDetail;
	}

StockDetail.java

...
public class StockDetail implements java.io.Serializable {
	private Stock stock;
        ...
        public Stock getStock() {
		return this.stock;
	}

	public void setStock(Stock stock) {
		this.stock = stock;
	}

Stock.hbm.xml

...
<class name="com.mkyong.common.Stock" table="stock" ...>
        <id name="stockId" type="java.lang.Integer">
            <column name="STOCK_ID" />
            <generator class="identity" />
        </id>
        ...
        <one-to-one name="stockDetail" class="com.mkyong.common.StockDetail" 
         cascade="save-update"></one-to-one>
        ...

StockDetail.hbm.xml

...
<class name="com.mkyong.common.StockDetail" table="stock_detail" ...>
        <id name="stockId" type="java.lang.Integer">
            <column name="STOCK_ID" />
            <generator class="foreign">
                <param name="property">stock</param>
            </generator>
        </id>
        <one-to-one name="stock" class="com.mkyong.common.Stock" 
        constrained="true"></one-to-one>
        ...

The main difficulty with one-to-one relationship is ensuring both are assigned the same primary key. In StockDetail.hbm.xml, a special foreign identifier generator is declared, it will know get the primary key value from STOCK table. With constrained=”true”, it ensure the Stock must exists.

2. Hibernate annotation

In annotation way, only two classes are required, all the relationships are declared inside the Java classes.

Stock.java -> STOCK table
StockDetail.java -> STOCK_DETAIL table

Stock.java

...
@Entity
@Table(name = "stock", catalog = "mkyong", uniqueConstraints = {
		@UniqueConstraint(columnNames = "STOCK_NAME"),
		@UniqueConstraint(columnNames = "STOCK_CODE") })
public class Stock implements java.io.Serializable {
	private StockDetail stockDetail;
        ...
	@Id
	@GeneratedValue(strategy = GenerationType.IDENTITY)
	@Column(name = "STOCK_ID", unique = true, nullable = false)
	public Integer getStockId() {
		return this.stockId;
	}

	@OneToOne(fetch = FetchType.LAZY, mappedBy = "stock")
	@Cascade({CascadeType.SAVE_UPDATE})
	public StockDetail getStockDetail() {
		return this.stockDetail;
	}

StockDetail.java

@Entity
@Table(name = "stock_detail", catalog = "mkyong")
public class StockDetail implements java.io.Serializable {
	private Stock stock;
        ...
	@GenericGenerator(name = "generator",
            strategy = "foreign",
            parameters = @Parameter(name = "property", value = "stock"))
	@Id
	@GeneratedValue(generator = "generator")
	@Column(name = "STOCK_ID", unique = true, nullable = false)
	public Integer getStockId() {
		return this.stockId;
	}

	@OneToOne(fetch = FetchType.LAZY)
	@PrimaryKeyJoinColumn
	public Stock getStock() {
		return this.stock;
	}

The code is self-explanatory, all the @annotation are the XML mapping tag substitution.

Test It

Run the example, both annotation and XML mapping file will generate the same output. Hibernate inserts a row into the STOCK table and a row into the STOCK_DETAIL table.

        Stock stock = new Stock();

        stock.setStockCode("4715");
        stock.setStockName("GENM");

        StockDetail stockDetail = new StockDetail();
        stockDetail.setCompName("GENTING Malaysia");
        stockDetail.setCompDesc("Best resort in the world");
        stockDetail.setListedDate(new Date());

        stock.setStockDetail(stockDetail);
        stockDetail.setStock(stock);

        session.save(stock);

Output

Hibernate:
    INSERT INTO mkyong.stock
    (STOCK_CODE, STOCK_NAME)
    VALUES (?, ?)

Hibernate:
    INSERT INTO mkyong.stock_detail
    (COMP_NAME, COMP_DESC, REMARK, LISTED_DATE, STOCK_ID)
    VALUES (?, ?, ?, ?, ?)

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Hibernate – One-to-one relationship example

“One-to-one” example

Hibernate implementation

1. Hibernate XML mapping file

Stock.java

StockDetail.java

Stock.hbm.xml

StockDetail.hbm.xml

2. Hibernate annotation

Stock.java

StockDetail.java

Test It

Output

4 Responses to “Hibernate – One-to-one relationship example”

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