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I am planning to integrate ORM in my project, so i used eclipse's JPA project to generate entity classes out of old databases. In total 168 entity classes where generated and it's fine. But in some constraints like nullable, unique are not automatically generating.
For example I need something like this :-
@Column(name="USER_NAME",unique = true)
private String userName;
but after auto generating entities there is no unique constraint in code. How can I achieve this simply?
any suggestions will be useful.
315
A unique constraint can be either a column constraint or a table constraint. At the table level, we can define unique constraints across multiple columns. JPA allows us to define unique constraints in our code using @Column(unique=true) and @UniqueConstraint.
Implementing With a Foreign Key in JPA. Note that we place the @OneToOne annotation on the related entity field, Address. Also, we need to place the @JoinColumn annotation to configure the name of the column in the users table that maps to the primary key in the address table.
Annotation Type UniqueConstraintSpecifies that a unique constraint is to be included in the generated DDL for a primary or secondary table. Example: @Entity @Table( name="EMPLOYEE", uniqueConstraints= @UniqueConstraint(columnNames={"EMP_ID", "EMP_NAME"}) ) public class Employee { ... } Since: Java Persistence 1.0.
Like the text says: an entity must have an identifier to allow relationships. No identifier, no relationships. To be clear: If Customer has no id, it can still reference other entities. But it can't be referenced by others.
Check your JPA version in your eclipse, if you found lowest versions update it to latest one. Latest JPA creates all the constraints which we defined in database table.
hope this helps you.
162
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