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javahibernatejpamavenserialversionuid

Why doesn't the Hibernate generate a DDL with column for serialVersionUID?

I get this DDL (postgres target) when I add the goal hbm2ddl using the Maven plugin hibernate3-maven-plugin:

create table listing (
    id varchar(36) not null,
    hash_code int4 not null,
    version int4,
    name varchar(100),
    primary key (id)
);

I defined all the columns shown.

All examples of using that I have seen on the web of:

private static final long serialVersionUID = -8402611044513083864L;

never have a @Column annotation. My DDL does not have a column for it. Does anybody else's?

So how does the deserialization code in Java know what version of a class was serialized and stored vs the one that it is being deserialized into?

Solution

  • Serial version UID is used when object is serialized / deserialized.

    If you annotate your object as an JPA Entity you're not using a serialization but just transforming your object to another representation - as a row in the database table.
    When you fetch the row from the database, this data is used to create a new instance of object with properly set state.

    Serialization, on the other hand, is used if you want to construct a binary representation of your object and then recreate the object instance using deserialization process.

    Note that you can use serialization with JPA i.e. if you want to persist a field (within your JPA entity) which is neither a basic type, embeddable nor other entity but just a plain Java class which implements Serializable marker interface.
    However, in this case only this given field in your entity is using serialization/deserialization to put binary data into database column. Still - the serial version UID is not stored anywhere in the database.

    For more information about persistent fields (which are persisted and which are not) you can take a look at 2.2 Persistent Fields and Properties chapter in JPA 2.0 FR specification.