Hibernate hbm2ddl.auto, possible values, and what they do

问题

I am looking at the Hibernate hbm2ddl.auto configuration property and its possible values:

• validate
• update
• create
• create-drop

What do all these values do?

The Hibernate Reference Documentation only talks briefly about create-drop, but doesn't say anything about the other values:

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

I found very useful explanations in these Stack Overflow questions:

• Hibernate hbm2ddl.auto possible values and what they do?
• Schema is not dropped on hbmddl.auto = create.drop

But still nothing in the official documentation.

回答1:

The link you provided is already the official documentation. So, there's nothing more official and comprehensive as-of today.

So I guess the answer to your question is two-fold:

• either file an enhancement request in the Hibernate issue tracker (better with a proposal)
• or read the corresponding code

I know this isn't the perfect answer you dreamt about, but this is actually all you have today.

But the good news is that the project is open-source, so you have all you need to help improve it :-).

回答2:

For hbm2ddl.auto property the list of possible options is:

• validate: validate that the schema matches, make no changes to the schema of the database, you probably want this for production.
• update: update the schema to reflect the entities being persisted
• create: creates the schema necessary for your entities, destroying any previous data.
• create-drop: create the schema as in create above, but also drop the schema at the end of the session. This is great in early development or for testing.

回答3:

The documentation has been updated to include this information. Here is a link to the official, current documentation for this feature.

hibernate.hbm2ddl.auto (e.g. none (default value), create-only, drop, create, create-drop, validate, and update)

Setting to perform SchemaManagementTool actions automatically as part of the SessionFactory lifecycle. Valid options are defined by the externalHbm2ddlName value of the Action enum:

none
    No action will be performed.

create-only
    Database creation will be generated.

drop
    Database dropping will be generated.

create
    Database dropping will be generated followed by database creation.

create-drop
    Drop the schema and recreate it on SessionFactory startup. Additionally, drop the schema on SessionFactory shutdown.

validate
    Validate the database schema

update
    Update the database schema

来源：https://stackoverflow.com/questions/18077327/hibernate-hbm2ddl-auto-possible-values-and-what-they-do