CODEWITHSUNDEEP
javahibernatejpajoin
KS1
KS1

Reputation: 1039

JPA mapping of two tables using and when to use jointable

This is more of a general 'understanding' question rather than a specific senario question.

I have been lookiing at the ways in which JPA maps tables together and found two examples here that seem to work in different ways.

One has a Set of Phone objects using @JoinTable to join STUDENT_PHONE to STUDENT by STUDENT_ID

The other has a Set of StockDailyRecord but seems to just use mappedby stock and in the stock_detail table object have the @PrimaryKeyJoinColumn annotation.

Simply trying to get an understanding of which method would be the prefered way and why?

Method 1:

@OneToMany(cascade = CascadeType.ALL)
@JoinTable(name = "STUDENT_PHONE", joinColumns = { @JoinColumn(name = "STUDENT_ID") }, inverseJoinColumns = { @JoinColumn(name = "PHONE_ID") })
public Set<Phone> getStudentPhoneNumbers() {
    return this.studentPhoneNumbers;
}

Method 2:

@Table(name = "stock", catalog = "mkyongdb", uniqueConstraints = {
    @UniqueConstraint(columnNames = "STOCK_NAME"),
    @UniqueConstraint(columnNames = "STOCK_CODE") })


@OneToMany(fetch = FetchType.LAZY, mappedBy = "stock")
public Set<StockDailyRecord> getStockDailyRecords() {
    return this.stockDailyRecords;
}


@Table(name = "stock_detail", catalog = "mkyongdb")

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

Upvotes: 0

Views: 570

Answers (1)

Jay
Jay

Reputation: 9509

Method #2:

It uses an extra column to build the OneToMany relation. This column is a Foreign key column of the other table. Before building the relation if these data needs to be added to the database then this foreign key column needs to be defined as nullable. This breaks the efficiency and cannot provide a normalized schema.

Method #1:

It uses a third table and is the efficient way to store data in a relational database and provides a normalized schema. So where possible its better to use this approach, if the data needs to be existed before building the relation.

Upvotes: 1

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