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I have a j2ee application using hibernate with annotation. How do I annotate the Id field in my pojo class to set it as auto increment or auto generated. and in adding the bean do I leave that field in my bean null?
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If you want to use this strategy, you have to annotate the primary key attribute @Id and with the @GeneratedValue annotation and set the strategy attribute to GenerationType. IDENTITY. If you now persist a new Author entity, Hibernate will use the auto-incremented database column to generate the primary key value.
In order to use this feature, we just need to declare an id of type UUID with @GeneratedValue annotation: @Entity public class Course { @Id @GeneratedValue private UUID courseId; // ... } Hibernate will generate an id of the form “8dd5f315-9788-4d00-87bb-10eed9eff566”.
Identifiers model the primary key of an entity. They are used to uniquely identify each specific entity. Hibernate and JPA both make the following assumptions about the corresponding database column(s): UNIQUE - The values must uniquely identify each row. NOT NULL - The values cannot be null.
Yes, hibernate requires an Id. Sometimes if you are dealing with a legacy database that for whatever reason does not have a key, you can define the key in Hibernate to be a composite key of all the columns for example, as this will be guaranteed to be unique.
@Id @GeneratedValue(strategy=GenerationType.AUTO) private int id; and you leave it null (0) when persisting. (null if you use the Integer / Long wrappers)
In some cases the AUTO strategy is resolved to SEQUENCE rathen than to IDENTITY or TABLE, so you might want to manually set it to IDENTITY or TABLE (depending on the underlying database).
It seems SEQUENCE + specifying the sequence name worked for you.
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