What are the possible values of the Hibernate hbm2ddl.auto configuration and what do they do

java hibernate hbm2ddl

I really want to know more about the update, export and the values that could be given to hibernate.hbm2ddl.auto
I need to know when to use the update and when not? And what is the alternative?

These are changes that could happen over DB:

new tables

new columns in old tables

columns deleted

data type of a column changed

a type of a column changed its attributes

tables dropped

values of a column changed

In each case what is the best solution?

Community

From the community documentation:

hibernate.hbm2ddl.auto Automatically validates or exports schema DDL to the database when the SessionFactory is created. With create-drop, the database schema will be dropped when the SessionFactory is closed explicitly. e.g. validate | update | create | create-drop

So the list of possible options are,

validate: validate the schema, makes no changes to the database.

update: update the schema.

create: creates the schema, destroying previous data.

create-drop: drop the schema when the SessionFactory is closed explicitly, typically when the application is stopped.

none: does nothing with the schema, makes no changes to the database

These options seem intended to be developers tools and not to facilitate any production level databases, you may want to have a look at the following question; Hibernate: hbm2ddl.auto=update in production?

Just read the hibernate docu ... for valid values, it says: "e.g." ... are there any other valid values?

I think it says "e.g." because it's just a community documentation, if someone's interested in all the possible values, it can be found in Hibernate's javadoc. (And yes, only those four options are present) docs.jboss.org/hibernate/orm/4.1/javadocs/org/hibernate/cfg/…

validate says validate the schema , what exactly does it mean ??

You can also use 'aardvark', or 'pigeon' or any other word, if you want hibernate to do nothing. Not that I would recommend that of course!

A small addition to the create-drop option. If this option is used it does not drop the whole schema instead it drops the tables whose mappings are available while running this. For example if a database with Schema S has A, B, C tables and java code has mappings for A and B only then Hibernate will not drop the table C.

Michiel Verkaik

There's also the undocumented value of "none" to disable it entirely.

This is actually quite useful since Hibernate’s schema validation sometimes fails for perfectly valid schemas.

I was just about to ask for something like this. My intention is to reduce startup time.

'empty string' is better than 'none'. To use 'none', you will receive warning message: org.hibernate.cfg.SettingsFactory - Unrecognized value for "hibernate.hbm2ddl.auto": none

I've patched it. Added "none" as an explicitly valid constant.

I like "hibernate.hbm2ddl.auto=potato" over others stackoverflow.com/a/15810379/838444

Peter Hilton

The configuration property is called hibernate.hbm2ddl.auto

In our development environment we set hibernate.hbm2ddl.auto=create-drop to drop and create a clean database each time we deploy, so that our database is in a known state.

In theory, you can set hibernate.hbm2ddl.auto=update to update your database with changes to your model, but I would not trust that on a production database. An earlier version of the documentation said that this was experimental, at least; I do not know the current status.

Therefore, for our production database, do not set hibernate.hbm2ddl.auto - the default is to make no database changes. Instead, we manually create an SQL DDL update script that applies changes from one version to the next.

Actually, per the documentation, create-drop creates the database tables and drops them when the session factory is explicitly closed. It does not drop the tables when the session factory is created.

No, both create-drop and create drop the tables when the sessionfactory is created, then create-drop drops the tables also when sessionfactory is closed. See stackoverflow.com/a/6752698/1536382

does making hibernate.hbm2ddl.auto=create-drop in production can lead to several connection timeout in production ?

Vlad Mihalcea

First, the possible values for the hbm2ddl configuration property are the following ones:

none - No action is performed. The schema will not be generated.

create-only - The database schema will be generated.

drop - The database schema will be dropped.

create - The database schema will be dropped and created afterward.

create-drop - The database schema will be dropped and created afterward. Upon closing the SessionFactory, the database schema will be dropped.

validate - The database schema will be validated using the entity mappings.

update - The database schema will be updated by comparing the existing database schema with the entity mappings.

The hibernate.hbm2ddl.auto="update" is convenient but less flexible if you plan on adding functions or executing some custom scripts.

So, The most flexible approach is to use Flyway.

However, even if you use Flyway, you can still generate the initial migration script using hbm2ddl.

drop doesn't seem to be a valid option. Which version of hibernate are you referring to?

It's been a valid option since Hibernate 5.1, which was released in 2016. Check out the Action enum for more details. I assume you are using a very old Hibernate version.

what is the exact difference between validate vs update.

The answer tells the difference.

Pat

I would use liquibase for updating your db. hibernate's schema update feature is really only o.k. for a developer while they are developing new features. In a production situation, the db upgrade needs to be handled more carefully.

See stackoverflow.com/questions/221379/… for why you shouldn't use hbm2ddl for production.

amit

Although it is quite an old post but as i did some research on the topic so thought of sharing it.

hibernate.hbm2ddl.auto

As per the documentation it can have four valid values:

create | update | validate | create-drop

Following is the explanation of the behaviour shown by these value:

create :- create the schema, the data previously present (if there) in the schema is lost

update:- update the schema with the given values.

validate:- validate the schema. It makes no change in the DB.

create-drop:- create the schema with destroying the data previously present(if there). It also drop the database schema when the SessionFactory is closed.

Following are the important points worth noting:

In case of update, if schema is not present in the DB then the schema is created.

In case of validate, if schema does not exists in DB, it is not created. Instead, it will throw an error:- Table not found:

In case of create-drop, schema is not dropped on closing the session. It drops only on closing the SessionFactory.

In case if i give any value to this property(say abc, instead of above four values discussed above) or it is just left blank. It shows following behaviour: -If schema is not present in the DB:- It creates the schema -If schema is present in the DB:- update the schema.

It's indeed a very important point that schema will be created if it doesn't exist, when "update" is used.

create-drop is contradicted when compare "Explanation of the behaviour" and "Important Points" statements.

What's the difference between update and empty?

Tom

hibernate.hbm2ddl.auto automatically validates and exports DDL to the schema when the sessionFactory is created.

By default, it does not perform any creation or modification automatically on DB. If the user sets one of the below values then it is doing DDL schema changes automatically.

create - doing creating a schema

update - updating existing schema

validate - validate existing schema

create-drop - create and drop the schema automatically when a session is starts and ends

what about ?

Stefan Haberl

If you don't want to use Strings in your app and are looking for predefined constants have a look at org.hibernate.cfg.AvailableSettings class included in the Hibernate JAR, where you'll find a constant for all possible settings. In your case for example:

/**
 * Auto export/update schema using hbm2ddl tool. Valid values are <tt>update</tt>,
 * <tt>create</tt>, <tt>create-drop</tt> and <tt>validate</tt>.
 */
String HBM2DDL_AUTO = "hibernate.hbm2ddl.auto";

Why is reference to 700+ lines long source file above straight answer with almost 500 vole ups ?

... that question doesnt make any sense. Why are there things? Why am i even here?

Ravi K M

validate: validates the schema, no change happens to the database.

update: updates the schema with current execute query.

create: creates new schema every time, and destroys previous data.

create-drop: drops the schema when the application is stopped or SessionFactory is closed explicitly.

Whats the 'official' documentation reference? - just wondering...

Vishal Sharma

I Think you should have to concentrate on the

SchemaExport Class

this Class Makes Your Configuration Dynamic So it allows you to choose whatever suites you best...

Checkout [SchemaExport]

Arun Raaj

validate: It validates the schema and makes no changes to the DB.
Assume you have added a new column in the mapping file and perform the insert operation, it will throw an Exception "missing the XYZ column" because the existing schema is different than the object you are going to insert. If you alter the table by adding that new column manually then perform the Insert operation then it will definitely insert all columns along with the new column to the Table. Means it doesn't make any changes/alters the existing schema/table.

update: it alters the existing table in the database when you perform operation. You can add or remove columns with this option of hbm2ddl. But if you are going to add a new column that is 'NOT NULL' then it will ignore adding that particular column to the DB. Because the Table must be empty if you want to add a 'NOT NULL' column to the existing table.

Doc Davluz

Since 5.0, you can now find those values in a dedicated Enum: org.hibernate.boot.SchemaAutoTooling (enhanced with value NONE since 5.2).

Or even better, since 5.1, you can also use the org.hibernate.tool.schema.Action Enum which combines JPA 2 and "legacy" Hibernate DDL actions.

But, you cannot yet configure a DataSource programmatically with this. It would be nicer to use this combined with org.hibernate.cfg.AvailableSettings#HBM2DDL_AUTO but the current code expect a String value (excerpt taken from SessionFactoryBuilderImpl):

this.schemaAutoTooling = SchemaAutoTooling.interpret( (String) configurationSettings.get( AvailableSettings.HBM2DDL_AUTO ) );

… and internal enum values of both org.hibernate.boot.SchemaAutoToolingand org.hibernate.tool.schema.Action aren't exposed publicly.

Hereunder, a sample programmatic DataSource configuration (used in ones of my Spring Boot applications) which use a gambit thanks to .name().toLowerCase() but it only works with values without dash (not create-drop for instance):

@Bean(name = ENTITY_MANAGER_NAME)
public LocalContainerEntityManagerFactoryBean internalEntityManagerFactory(
        EntityManagerFactoryBuilder builder,
        @Qualifier(DATA_SOURCE_NAME) DataSource internalDataSource) {

    Map<String, Object> properties = new HashMap<>();
    properties.put(AvailableSettings.HBM2DDL_AUTO, SchemaAutoTooling.CREATE.name().toLowerCase());
    properties.put(AvailableSettings.DIALECT, H2Dialect.class.getName());

    return builder
            .dataSource(internalDataSource)
            .packages(JpaModelsScanEntry.class, Jsr310JpaConverters.class)
            .persistenceUnit(PERSISTENCE_UNIT_NAME)
            .properties(properties)
            .build();
}

Chaya Shetty

To whomever searching for default value...

It is written in the source code at version 2.0.5 of spring-boot and 1.1.0 at JpaProperties:

    /**
     * DDL mode. This is actually a shortcut for the "hibernate.hbm2ddl.auto"
     * property. Defaults to "create-drop" when using an embedded database and no
     * schema manager was detected. Otherwise, defaults to "none".
     */
    private String ddlAuto;

WesternGun

With all above said... Notice this property is called dll.auto and should only control dll operations(create/drop schema/table), I found surprisingly that it has to do with dml, too: only update will allow insert data, which is dml operation.

Got caught by this when trying to populate data into a in-memory database; only update works.

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