Hibernate hbm2ddl property - KK JavaTutorials

In our previous post Why to use hibernate dialect? we understood all the concept related to hibernate dialect property

In this post we will talk about hibernate hbm2ddl property in detail using an example.

Hibernate hbm2ddl property you can configure in your hibernate.cfg.xml as below

<property name="hibernate.hbm2ddl.auto">update</property>

1	<property name="hibernate.hbm2ddl.auto">update</property>

The possible values for hibernate.hbm2ddl.auto are:

create
validate
update
create-drop

Create

If the value is CREATE then hibernate first drops the existing database table/tables, then creates a new table/tables and then executes operations on newly created table.

The only problem with the value “create” is, we loose existing table data.

Let’s modify hibernate.cfg.xml for hibernate.hbm2ddl.auto property as below

<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
    "-//Hibernate/Hibernate Configuration DTD//EN"
    "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">

<hibernate-configuration>
	<session-factory>
	<property name="hibernate.connection.driver_class">com.mysql.cj.jdbc.Driver</property>
		<property name="hibernate.connection.url">jdbc:mysql://localhost:4406/test</property>
		<property name="hibernate.connection.username">root</property>
		<property name="hibernate.connection.password">root</property>
		<property name="hibernate.dialect">org.hibernate.dialect.MySQL5Dialect</property>
		<property name="hibernate.hbm2ddl.auto">create</property>
		<property name="hibernate.show_sql">true</property>
		<property name="hibernate.format_sql">true</property>
		
		<mapping class="com.infotech.entities.Employee"/>
	</session-factory>
</hibernate-configuration>

<?xml version='1.0' encoding='utf-8'?>

<!DOCTYPE hibernate-configuration PUBLIC

"-//Hibernate/Hibernate Configuration DTD//EN"

"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">

<hibernate-configuration>

<session-factory>

<property name="hibernate.connection.driver_class">com.mysql.cj.jdbc.Driver</property>

<property name="hibernate.connection.url">jdbc:mysql://localhost:4406/test</property>

<property name="hibernate.dialect">org.hibernate.dialect.MySQL5Dialect</property>

<property name="hibernate.hbm2ddl.auto">create</property>

</session-factory>

</hibernate-configuration>

Now login to your MYSQL database console and connect with database schema(test)

After Running ClientTest.java with createEmployee(employeeService) (Demo project) method.

The output of Eclipse console and MySqlWorkbench are as below in this case

Hibernate: 
    
    drop table if exists employee_table
Jul 04, 2018 9:24:09 AM org.hibernate.resource.transaction.backend.jdbc.internal.DdlTransactionIsolatorNonJtaImpl getIsolatedConnection
INFO: HHH10001501: Connection obtained from JdbcConnectionAccess [org.hibernate.engine.jdbc.env.internal.JdbcEnvironmentInitiator$ConnectionProviderJdbcConnectionAccess@2072acb2] for (non-JTA) DDL execution was not in auto-commit mode; the Connection 'local transaction' will be committed and the Connection will be set into auto-commit mode.
Hibernate: 
    
    create table employee_table (
       employee_id integer not null auto_increment,
        date_of_joing datetime,
        email varchar(255),
        employee_name varchar(100) not null,
        salary double precision,
        primary key (employee_id)
    ) engine=MyISAM
Jul 04, 2018 9:24:09 AM org.hibernate.resource.transaction.backend.jdbc.internal.DdlTransactionIsolatorNonJtaImpl getIsolatedConnection
INFO: HHH10001501: Connection obtained from JdbcConnectionAccess [org.hibernate.engine.jdbc.env.internal.JdbcEnvironmentInitiator$ConnectionProviderJdbcConnectionAccess@6f152006] for (non-JTA) DDL execution was not in auto-commit mode; the Connection 'local transaction' will be committed and the Connection will be set into auto-commit mode.
Hibernate: 
    
    alter table employee_table 
       add constraint UK_2casspobvavvi9s23312f9mhm unique (email)
Jul 04, 2018 9:24:10 AM org.hibernate.tool.schema.internal.SchemaCreatorImpl applyImportSources
INFO: HHH000476: Executing import script 'org.hibernate.tool.schema.internal.exec.ScriptSourceInputNonExistentImpl@49872d67'
Hibernate: 
    insert 
    into
        employee_table
        (date_of_joing, email, employee_name, salary) 
    values
        (?, ?, ?, ?)
Employee is created  with Id::1

Hibernate:

drop table if exists employee_table

Jul 04, 2018 9:24:09 AM org.hibernate.resource.transaction.backend.jdbc.internal.DdlTransactionIsolatorNonJtaImpl getIsolatedConnection

INFO: HHH10001501: Connection obtained from JdbcConnectionAccess [org.hibernate.engine.jdbc.env.internal.JdbcEnvironmentInitiator$ConnectionProviderJdbcConnectionAccess@2072acb2] for (non-JTA) DDL execution was not in auto-commit mode; the Connection 'local transaction' will be committed and the Connection will be set into auto-commit mode.

Hibernate:

create table employee_table (

employee_id integer not null auto_increment,

date_of_joing datetime,

email varchar(255),

employee_name varchar(100) not null,

salary double precision,

primary key (employee_id)

) engine=MyISAM

Jul 04, 2018 9:24:09 AM org.hibernate.resource.transaction.backend.jdbc.internal.DdlTransactionIsolatorNonJtaImpl getIsolatedConnection

INFO: HHH10001501: Connection obtained from JdbcConnectionAccess [org.hibernate.engine.jdbc.env.internal.JdbcEnvironmentInitiator$ConnectionProviderJdbcConnectionAccess@6f152006] for (non-JTA) DDL execution was not in auto-commit mode; the Connection 'local transaction' will be committed and the Connection will be set into auto-commit mode.

Hibernate:

alter table employee_table

add constraint UK_2casspobvavvi9s23312f9mhm unique (email)

Jul 04, 2018 9:24:10 AM org.hibernate.tool.schema.internal.SchemaCreatorImpl applyImportSources

INFO: HHH000476: Executing import script 'org.hibernate.tool.schema.internal.exec.ScriptSourceInputNonExistentImpl@49872d67'

Hibernate:

insert

into

employee_table

(date_of_joing, email, employee_name, salary)

values

(?, ?, ?, ?)

Employee is created with Id::1

validate

If the value is validate then hibernate only validates whether the table and columns are exist or not. If the table doesn’t exist then hibernate throws an exception.

update

If the value is update then, Hibernate checks for the table and columns. If table doesn’t exist then it creates a new table and if a column doesn’t exist it creates new column for it.

But in the case of value “update” hibernate doesn’t drop any existing table, here we doesn’t lose existing table or data.

create-drop

If the value is create-drop then, Hibernate first checks for a table and do the necessary operations and finally drops the table after all the operations are completed.

The value “create-drop” is given for unit testing/POC kind of functionalities in the hibernate.

Now let’s have a practical example to understand how hibernate hbm2ddl property works with different options(create,validate,update,create-drop)

To proceed with this demo we will refer our Hibernate CRUD(Create,Read,Update and Delete) example

That’s all about Hibernate hbm2ddl property

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