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[jsr338-experts] Re: JPA schema generation

  • From: Gordon Yorke <gordon.yorke@...>
  • To: jsr338-experts@...
  • Subject: [jsr338-experts] Re: JPA schema generation
  • Date: Tue, 15 May 2012 16:22:05 -0300

Hello Linda,
   Please find some feedback below.
--Gordon

On 09/05/2012 3:36 PM, Linda DeMichiel wrote:

In conjunction with support for use of JPA in PaaS environments, we
will need to address the issue of schema generation.  After we discuss
this area, I'd like to return to a broader discussion of multitenancy
support with this in view.


Here's what I think we'll need to address:

1.  How/when schema generation happens:
    a. at a deployment time phase (or predeployment time phase)
    b. at EMF creation time

2.  Providing an option whereby the application can supply DDL for
    schema generation as an alternative to the persistence provider
    doing schema generation based on the ORM metadata

3.  How, once schema generation has happened, tables can get loaded with
    data.  If we enable the application to provide DDL scripts for
    schema generation, then supporting the use of SQL bulk insert scripts
    would go hand-in-hand with this, but perhaps there are also other
    approaches, e.g., bulk insert via JPQL(?).

4.  The need for additional ORM metadata:  e.g. metadata for index
    generation; for foreign key constraints; other(?).

5.  More precise definition of existing metadata that can be used
    for schema generation:  what it comprises, and how it can/must
    be used.

6.  Additional persistence.xml level metadata and additional metadata
    the platform provider passes to the persistence provider to control
    or configure the operations outlined above.


I am assuming for that Java EE 7 we need to support both the
separate database and shared database (aka separate schema) approaches.

I am also assuming that it is the platform provider that does the
provisioning of either the database or the schema respectively (i.e.,
in accordance with whether the separate database or shared database
approach is taken).   I.e., in the separate database approach, I'm
assuming that it is the persistence provider that creates the schemas
directly in the database or creates the DDL to generate the schemas
needed for the persistence unit.  [I'll use the term "schema
generation" generically below to mean either table generation or
schema+table generation with this assumption in view.]


Here's a proposal to get the discussion started.

SCHEMA GENERATION

I think we should allow schema generation to be done either as a
deployment (or pre-deployment) phase or at createEMF time.
Both would be a good. We currently support ddl generation at createEMF time, expanding the new functionality to this point in time seems like a good idea as well

Deployment-time (or predeployment-time) schema generation could be
done either by the platform provider calling into the
PersistenceProvider implementation to generate the database schema or
by the platform provider running SQL DDL scripts.
Or a combination of both. Should the deployer require specific structures not supported by the persistence provider, the provider could have the bulk of the generation completed by the persistence provider then tweak the db structures with scripts.

SQL DDL scripts might be provided with the application (bundled as
part of the persistence unit) or the platform provider might invoke
the PersistenceProvider implementation to generate them from the
persistence unit metadata.  If scripts are provided or generated, it
should be the platform provider's responsibility to run them against
Do you mean it is the platform provider's responsibility to invoke the deployment time interfaces of the persistence provider to have the scripts run? If we are going to have the functionality available in the persistence provider we should keep the roles distinct.
the database.  If the application has provided DDL scripts, the
application should also have the option to provide SQL scripts to do
a bulk insert of data.  It would be the responsibility of the
platform provider to run these as well.

An alternative to the use of scripts is for the platform provider to
call into the PersistenceProvider to directly generate the tables in
the database.  In the case that a database has been provisioned rather
than only a schema, the persistence provider would generate the
schemas and tables.
It may be problematic to have persistence providers generate schema. In many databases user security permissions would need to be updated to allow access to the new schema and there is currently no metadata to define users and their security permissions. Defining that metadata may be more than we want the spec to take on. We should require the platform provider to provision users along with the database.

For the sake of argument, let's assume that we add a generateSchema()
method to the PersistenceProvider interface, which the platform
provider invokes during the deployment phase if SQL scripts have not
been provided by the application.

Information that needs to be passed in would include the following:

(1) Information that specifies how schema generation is to proceed.
    This information could take the form of a SchemaGenerationInfo
interface or it could be in the form of additional standard properties.
(2) Connection to the database or schema.  [Is this a Connection or a
    DataSource ?]
We should use the current createEMF APIs where connection info or a datasource can be provided. We may want to put these new APIs on the EMF
(3) PersistenceUnitInfo
We should allow for SE type deployments as well where the persistence provider discovers the PUInfo. The platform provider may not be a EE platform and should not be required to implement that role in the SPI.



The SchemaGenerationInfo should include the following:

ddl-generation-mode: GENERATE_AND_EXECUTE | GENERATE_ONLY | EXECUTE_ONLY

GENERATE_AND_EXECUTE => generate ddl scripts and generate schema (if
        applicable) and tables directly in the database

      GENERATE_ONLY => generate ddl scripts

EXECUTE_ONLY => generate schema (if applicable) and tables directly in
         the database

  create-ddl-target:  a Writer configured for the persistence provider
for outputting of the DDL scripts for the creation of schema/tables.
This should be null if EXECUTE_ONLY ddl-generation-mode is specified.

  drop-ddl-target: a Writer configured for the persistence provider
for outputting of the DDL scripts for the dropping of schema/tables.
The should be null if EXECUTE_ONLY ddl-generation-mode is specified.

  ddl-execution-mode: Used when executing directly against the database,
      rather than generating scripts.  Options should include:
       CREATE_TABLES | DROP_TABLES | DROP_AND_CREATE_TABLES
Do we also need to distinguish CREATE_SCHEMAS_AND_TABLES ? DROP_SCHEMA ?
       Or can these be implicit?
Schema generation should be implicit.
     Do we also need an ALTER_TABLES capability here?
Perhaps optionally.

  properties:  These could include any vendor-specific properties


ADDITIONAL METADATA (persistence.xml)

If scripts are provided with the application (i.e., bundled as part
of the persistence unit), we should add entries in the persistence.xml
to identify them:
      create-ddl-script
      drop-ddl-script
data-load-script(s) [Do we need to support more than one load script?
         If so, the ordering may need to be specified as well.]

Open issue: do we need metadata in the persistence.xml for
  ddl-execution-mode as well?  For example, this might be used in
  standalone scenarios (?)
Properties should be sufficient for this metadata.


ORM METADATA (annotations and orm.xml)

(1) Indexes

I think we need to support indexes.

Here's a strawman annotation:

  @Target({}) @Retention(RUNTIME)
  public @interface Index {
    String name() default "";
    String columnList();
  }

  The columnList syntax could follow that of the OrderBy annotation:

    columnList::= indexColumn [, indexColumn]*
    indexColumn::= columnName [ASC | DESC]

    If ASC or DESC is not specified, ASC is assumed

We'd also need to add
   Index[] indexes() default {};
to Table, Secondary Table, CollectionTable, JoinTable, and TableGenerator


(2) Foreign Key Constraints
We also have the user supplied scripts to fall back on. If the persistence provider's functionality is insufficient scripts can be deployed as well. FK definition is likely to devolve into a definition string.

I see two possible approaches:

(a) Add a string-valued foreignKeyDefinition element to JoinColumn,
JoinColumns, MapKeyJoinColumn, etc. to specify a SQL fragment
(intended along the lines of columnDefinition) for defining a foreign
key constraint and/or for overriding the persistence provider's
default foreign key definition.  It might also be helpful to allow a
name for the foreign key constraint to be specified for the case where
the provider is using its default foreign key generation strategy.

or

(b) Add a ForeignKey annotation to specify the foreign key constraint --
for example,

public @interface ForeignKey {
  String name() default "";
  ForeignKeyAction updateAction() default NO_ACTION;
  ForeignKeyAction deleteAction() default NO_ACTION;
  boolean deferred() default false;
}

public enum ForeignKeyAction {NO_ACTION, CASCADE, SET_NULL};

I have some misgivings about approach (b), and, given a lack of
database portability here, we might wind up needing a foreignKeyDefinition
fragment anyway.


(3) Other

What about the ability to distinguish a CHAR rather than VARCHAR
mapping for strings?  Or should we just leave this as belonging in a
SQL fragment (with the understanding that we would be intentionally
discouraging the use of CHAR strings)?
The fragment should be sufficient.

(4) Anything else I'm missing?


APIs

I assumed the addition of a PersistenceProvider.generateSchema() method
above.
This generateSchema() method should be placed on the EMF. The there is no need to have a separate API on PersistenceProvider.

If we also support schema generation at EMF creation time, do we want
another createContainerEntityManagerFactory() method that takes a
SchemaGenerationInfo as well as PersistenceUnitInfo argument ?
Having the GenerationInfo contents supplied through properties means we do not need new APIs.

If generation is done directly in the database, at some point the
container (or application) may need to have the schema/tables dropped.
I'm not sure of the best way to support this.   A dropAndClose() method
on the EMF??





[jsr338-experts] Re: JPA schema generation

(continued)

[jsr338-experts] Re: JPA schema generation

Evan Ireland 05/09/2012

[jsr338-experts] Re: JPA schema generation

Nicolas Seyvet 05/10/2012

[jsr338-experts] Re: JPA schema generation

Linda DeMichiel 05/15/2012

[jsr338-experts] Re: JPA schema generation

Steve Ebersole 05/15/2012

[jsr338-experts] Re: JPA schema generation

Linda DeMichiel 05/15/2012

[jsr338-experts] Re: JPA schema generation

Steve Ebersole 05/15/2012

[jsr338-experts] Re: JPA schema generation

Linda DeMichiel 05/15/2012

[jsr338-experts] Re: JPA schema generation

Steve Ebersole 05/15/2012

[jsr338-experts] Re: JPA schema generation

Linda DeMichiel 05/21/2012

[jsr338-experts] Re: JPA schema generation

Rainer Kwesi Schweigkoffer 05/22/2012

[jsr338-experts] Re: JPA schema generation

Gordon Yorke 05/15/2012

[jsr338-experts] Re: JPA schema generation

Linda DeMichiel 05/15/2012

[jsr338-experts] Re: JPA schema generation

Gordon Yorke 05/15/2012

[jsr338-experts] Re: JPA schema generation

Steve Ebersole 05/17/2012

[jsr338-experts] Re: JPA schema generation

Linda DeMichiel 05/18/2012

[jsr338-experts] Re: JPA schema generation

Steve Ebersole 05/18/2012

[jsr338-experts] Re: JPA schema generation

Linda DeMichiel 05/18/2012

[jsr338-experts] Re: JPA schema generation

Steve Ebersole 05/21/2012

[jsr338-experts] Re: JPA schema generation

Linda DeMichiel 05/22/2012
 
 
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