Functional Specification: New Native Object-Relational Mapping XML

ER 200040

Document History

Date	Author	Version Description & Notes
2007-11-15	Guy Pelletier	Initial Draft
2007-11-20	Doug Clarke	Flushing out requirements and functionality sections
2007-11-26	Guy Pelletier	Further flushing out requirements and functionality sections

Project overview

This project will introduce a new native XML configuration file that can be used to define the object-relational mapping metadata the EclipseLink runtime will use.

Goals:

Improve the usability of the native ORM.XML file by making it more readable and less verbose (configuration by exception). Naming will align with JPA's ORM.XML to make usage of the native ORM.XML as intuitive as possible.
Support various usage scenarios
- As standalone mapping file(s) replacing the existing deployment project/map XML
- As an override for JPA's ORM.XML enabled fine grain customization

Note this project will not address our OXM (JAXB, SDO) and EIS functionality. Those technologies will be addressed at a later time and should provide their own schema definitions etc. This project will concentrate solely on the ORM features available from EclipseLink.

Concepts

The following concepts are used in the document:

ORM.XML refers to the JPA specification defined XML configuration file which can be used within a persistence unit through reference in the persistence.xml or through default location (META-INF/orm.xml)
EclipseLink-ORM.XML (EL-ORM.XML) – EclipseLink’s native metadata XML file which is being defined along with its usage within this project.

Requirements

The following sections will expand the goals of this project into more concrete requirements.

EclipseLink-ORM.XML XSD

A new XSD for defining EclipseLink's object-relational metadata will be defined:

Must support the complete functionality of the existing deployment project/map XML plus any additional features developed in parallel or selected for inclusion during the design process.
Must align with JPA's ORM.XML to make it both intuitive to use and also facilitate overriding. The new XSD will not import or reference JPA's ORM.XML but must instead align with it through common element and attribute naming (it should grab JPA's namespace where available).
Must embrace configuration by exception so only scope and non-default configurations need to be specified.
Must embrace minimal config, ORM.XML alignment for overrides, and complete configuration without any JPA annotations or XML.
Ensure we can have a persistence unit defined with no entities. If a customer just wants to access the database using SQL or stored procedures they should be able to define a persistence unit with zero entities and just the named queries.
Be able to have named native SQL and stored procedure queries where the results can be shaped using any arbitrary entity or non-entity class. I think of this as constructor results for native queries.

The EclipseLink-ORM.XML schema will be built from the existing ORM.XML schema. The EclipseLink-ORM.XML schema will need to relax any requirements that are present in the JPA XSD. Currently no elements as a whole are required only certain attributes within specified elements are required in the ORM.XML schema. Those elements and their requirements are as follows:

Element	Required attribute(s)
<entity-mappings>	version
<entity>, <entity-listener>, <id-class>, <embeddable>, <mapped-superclass>	class
<pre-persist>, <post-persist>, <pre-remove>, <post-remove>, <pre-update>, <post-update>, <post-load>	method-name
<query-hint>	name, value
<named-query>, <named-native-query>, <sql-result-set-mapping>, <id>, <embedded-id>, <transient>, <version>, <column-result>, <secondary-table>, <attribute-override>, <association-override>, <basic>, <many-to-one>, <one-to-one>, <one-to-many>, <many-to-many>, <embedded>, <sequence-generator>, <table-generator>	name
<entity-result>	entity-class
<field-result>	name, column

Therefore, the current minimal configuration for an ORM.XML file is:

<?xml version="1.0" encoding="UTF-8"?>
<entity-mappings version="1.0" 
   xmlns="http://java.sun.com/xml/ns/persistence/orm" 
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
   xsi:schemaLocation="http://java.sun.com/xml/ns/persistence/orm orm_1_0.xsd">
</entity-mappings>

The EclipseLink-ORM.XML schema will need to ensure this minimal configuration remains in place meaning we can load both the ORM.XML and EclipseLink-ORM.XML against the same internal MOXy project.

EclipseLink-ORM.XML Processing

The usage of EclipseLink-ORM.XML file(s) will conform to the following processing rules:

Design a runtime architecture that leverages MOXy for metadata loading in conjunction with annotations. This must handle JPA (annotations + ORM.XML) as well as additional native EclipseLink options (annotations + EclipseLink-ORM.XML).
Expand EclipseLink’s feature availability within the EclipseLink-ORM.XML beyond what is currently available.
- See Open Issues section #5
Support multiple metadata loading schemes
1. JPA only (annotations and XML)
2. EclipseLink Native only (native annotations and XML)
3. Oracle TopLink only: Support reading in and using Orcale TopLink's 11gR1 and 10.1.3 XML configuration files
4. JPA + EclipseLink Native
5. JPA + Oracle TopLink – Currently not supported, adding to the Open Issues section. User's cannot load JPA against an existing Oracle TopLink server-session/project. They are mutually exclusive.

EclipseLink-ORM.XML Locations

Developers will be able to leverage the EclipseLink-ORM.XML file for the purposes of JPA configuration. There are a number of ways the EclipseLink-ORM.XML file can be used.

Usage of the EclipseLink-ORM.XML file as an override for JPA and EclipseLink annotations and/or ORM.XML. The files can be referenced for inclusion in a persistence unit's metadata definition through:

Default location
1. META-INF/eclipselink-orm.xml
2. META-INF/orm.xml (in place of JPA's ORM.XML. Note: This most certainly will not be portable)
3. Referenced as persistence unit mapping file in persistence.xml
4. Referenced through session configuration (sessions.xml)

Default Locations

As with JPA's default assumption that the existence of a META-INF/orm.xml indicates that it should be used for any persistence unit, EclipseLink will have a default assumption that the existence of META-INF/eclipselink-orm.xml will be used. This file can exist in addition to JPA's META-INF/orm.xml as an override or in isolation.

The runtime will also support the default JPA META-INF/orm.xml being an EclipseLink ORM configuration file.

When both a META-INF/orm.xml and META-INF/eclipselink-orm.xml are specified, the contents of the META-INF/eclipselink-orm.xml will overlay the contents of the META-INF/orm.xml file or any other JPA mapping file.

EclipseLink-ORM.XML Override and Merging

The EclipseLink-ORM.XML override will only occur when the user defines the following file:

META-INF/eclipselink-orm.xml

Any other mapping file, regardless if it conforms to the EclipseLink-ORM.XML schema will be treated no differently than any other JPA ORM.XML file. If they are overlapping specifications in multiple orm files, the last file read will win and there is no guarantee in which order the mapping files will be processed. NOTE: The order the files are listed in the persistence.xml file does not not guarantee that they will be processed in that order.

The overall overriding rule will be at the 'mapping' level. However, the following sections below outline those elements already defined in the ORM.XML (hence can be specified in the EclipseLink-ORM.XML file) and their specific overriding in greater detail.

Also note that even though this file may provide extensions to entities in other mapping files it may also at the same time provide complete specifications of other entities and classes.

persistence-unit-metadata (and persistence-unit-defaults) override and merging rules

Currently a persistence-unit-metadata specification is to be defined in one and only one mapping file and is is an error to do otherwise (unless the specifications are identical). In the EclipseLink-ORM.XML case, a persistence-unit-metadata specification will merge and/or override the values of existing persistence-unit-metadata specification.

entity-mappings/persistence-unit-metadata	Rule	Comments
xml-mapping-metadata-complete	Full override	Any xml-mapping-unit-metadata setting will override an existing setting or set one
persistence-unit-defaults/schema	Full override	Any schema setting will override an existing setting or set one
persistence-unit-defaults/catalog	Full override	Any catalog setting will override an existing setting or set one
persistence-unit-defaults/access	Full override	Any access setting will override an existing setting or set one
entity-mappings/persistence-unit-metadata/persistence-unit-defaults/cascade-persist	Full override	Any cascade-persist setting will override an existing setting or set one
entity-mappings/persistence-unit-metadata/persistence-unit-defaults/entity-listeners	Full override	Any listeners defined here will override existing listeners and add new ones

entity-mappings override and merging rules

entity-mappings/	Rule	Comments
package	None	The package element specifies the package of the classes listed within the subelements and attributes of the same mapping file only. That is, will only apply to those entities that are fully defined within the EclipseLink-ORM.XML file, othwerwise it's usage remains local and the same as described in the JPA spec.
catalog	None	The catalog element applies only to the subelements and attributes listed within the EclipseLink-ORM.XML file that are NOT an extension to another mapping file. Otherwise, the use of the catalog element within the EclipseLink-ORM.XML file remains local and the same as described in the JPA spec.
schema	None	The schema element applies only to the subelements and attributes listed within the EclipseLink-ORM.XML file that are NOT an extension to another mapping file. Otherwise, the use of the schema element within the EclipseLink-ORM.XML file remains local and the same as described in the JPA spec.
access	None	The access element applies only to the subelements and attributes listed within the EclipseLink-ORM.XML file that are NOT an extension to another mapping file. Otherwise, the use of the access element within the EclipseLink-ORM.XML file remains local and the same as described in the JPA spec.
sequence-generator	Full override	A sequence-generator is unique by name. A sequence-generator with the same named defined in another mapping file will be completely overridden by this sequence-generator. Two sequence-generator's with the same name defined in the EclipseLink-ORM.XML file will cause an exception to be thrown.
table-generator	Full override	A table-generator is unique by name. A table-generator with the same named defined in another mapping file will be completely overridden by this table-generator. Two table-generator's with the same name defined in the EclipseLink-ORM.XML file will cause an exception to be thrown.
named-query	Full override	A named-query is unique by name. A named-query with the same named defined in another mapping file will be completely overridden by this named-query. Two named-query's with the same name defined in the EclipseLink-ORM.XML file will produce unexpected results as the last one read wins.
named-native-query	Full override	A named-native-query is unique by name. A named-native-query with the same named defined in another mapping file will be completely overridden by this named-native-query. Two named-native-query's with the same name defined in the EclipseLink-ORM.XML file will produce unexpected results as the last one read wins.
sql-result-set-mapping	Full override	A sql-result-set-mapping is unique by name. A sql-result-set-mapping with the same named defined in another mapping file will be completely overridden by this sql-result-set-mapping.

mapped-superclass override and merging rules

A mapped-superclass can be defined wholely or may be defined so as to provide extensions to a mapped-superclass from another mapping file. Therefore, we will allow the merging of that classes metadata. The individual override rules for that metadata is tabled below.

entity-mappings/mapped-superclass	Rule	Comments
id-class	Full override	An id-class setting will override an existing setting or set one
exclude-default-listeners	Full override	An exclude-default-listeners setting will override an existing setting or set one
exclude-superclass-listeners	Full override	An exclude-superclass-listeners setting will override an existing setting or set one
entity-listeners	Full override	Any listeners defined here will override existing listeners and add new ones
pre-persist	Full override	A pre-persist setting will override an existing setting or set one
post-persist	Full override	A post-persist setting will override an existing setting or set one
pre-remove	Full override	A pre-remove setting will override an existing setting or set one
post-remove	Full override	A post-remove setting will override an existing setting or set one
pre-update	Full override	A pre-update setting will override an existing setting or set one
post-update	Full override	A post-update setting will override an existing setting or set one
post-load	Full override	A post-load setting will override an existing setting or set one
attributes	Full override and merge	All attributes will be overriden at the mapping level (id, embedded-id, basic, version, many-to-one, one-to-many, one-to-one, many-to-many, embedded, transient) and new attributes will be added.
class	None
access	Full override	An access setting will override an existing setting or set one
metadata-complete	Full override	A metadata-complete setting will override an existing setting or set one

entity override and merging rules

An entity can be defined wholely or may be defined so as to provide extensions to an entity from another mapping file. In which case the overriding rule will be at a mapping level.

entity-mappings/entity	Rule	Comments
table	Full override	Any table specification assumes complete specification, including table, secondary-table and primary-key-join-column
secondary-table	Full override	Any table specification assumes complete specification, including table, secondary-table and primary-key-join-column
primary-key-join-column	Full override	Any table specification assumes complete specification, including table, secondary-table and primary-key-join-column
id-class	Full override	An id-class setting will override an existing setting or set one
inheritance	Full override
discriminator-value	Full override
discriminator-column	Full override
sequence-generator	Full override	A sequence-generator is unique by name. A sequence-generator with the same named defined in another mapping file will be completely overridden by this sequence-generator. Two sequence-generator's with the same name defined in the EclipseLink-ORM.XML file will cause an exception to be thrown.
table-generator	Full override	A table-generator is unique by name. A table-generator with the same named defined in another mapping file will be completely overridden by this table-generator. Two table-generator's with the same name defined in the EclipseLink-ORM.XML file will cause an exception to be thrown.
named-query	Full override	A named-query is unique by name. A named-query with the same named defined in another mapping file will be completely overridden by this named-query. Two named-query's with the same name defined in the EclipseLink-ORM.XML file will produce unexpected results as the last one read wins.
named-native-query	Full override	A named-native-query is unique by name. A named-native-query with the same named defined in another mapping file will be completely overridden by this named-native-query. Two named-native-query's with the same name defined in the EclipseLink-ORM.XML file will produce unexpected results as the last one read wins.
sql-result-set-mapping	Full override	A sql-result-set-mapping is unique by name. A sql-result-set-mapping with the same named defined in another mapping file will be completely overridden by this sql-result-set-mapping.
exclude-default-listeners	Full override	An exclude-default-listeners setting will override an existing setting or set one
exclude-superclass-listeners	Full override	An exclude-superclass-listeners setting will override an existing setting or set one
entity-listeners	Full override	Any listeners defined here will override existing listeners and add new ones
pre-persist	Full override	A pre-persist setting will override an existing setting or set one
post-persist	Full override	A post-persist setting will override an existing setting or set one
pre-remove	Full override	A pre-remove setting will override an existing setting or set one
post-remove	Full override	A post-remove setting will override an existing setting or set one
pre-update	Full override	A pre-update setting will override an existing setting or set one
post-update	Full override	A post-update setting will override an existing setting or set one
post-load	Full override	A post-load setting will override an existing setting or set one
attributes	Full override and merge	All attributes will be overriden at the mapping level (id, embedded-id, basic, version, many-to-one, one-to-many, one-to-one, many-to-many, embedded, transient) and new attributes will be added.
association-override	Full override
attributes	Full override and merge	At the mapping level (id, embedded-id, basic, version, many-to-one, one-to-many, one-to-one, many-to-many, embedded, transient)
name	Override
class	None
access	Override
metadata-complete	Override

embeddable override and merging rules

An embeddable can be defined wholely or may be defined so as to provide extensions to a mapped superclass from another mapping file.

entity-mappings/embeddable	Rule	Comments
attributes	Override and merge	At the mapping level (id, embedded-id, basic, version, many-to-one, one-to-many, one-to-one, many-to-many, embedded, transient)
class	None
access	Override
metadata-complete	Override

Use cases

Use case 1

META-INF/orm.xml - defines Entity A with the mappings b and c.
META-INF/eclipse-orm.xml - defines Entity A with the mappings for c and d.
Result - Entity A will contain the mapping b (from orm.xml), mapping c and d (from eclipse-orm.xml)

Use case 2

META-INF/orm.xml - defines Entity A with the mappings b and c
META-INF/some-other-mapping-file.xml - defines Entity B with the mappings a and b
META-INF/eclipse-orm.xml - defines Entity A with the mappings for c and d and Entity B with the mapping b and c
Result
- Entity A will contain the mapping b (from orm.xml), mapping c and d (from eclipse-orm.xml)
- Entity B will contain the mapping a (from some-other-mapping-file), mappings b and c (from eclipse-orm.xml)

Use case 3

META-INF/orm.xml - defines Entity A with the mappings b and c.
META-INF/eclipse-orm.xml - defines Entity A with the mappings c and d.
META-INF/some-other-mapping-file.xml - defines Entity A with the mapping x.
Result - Ambiguous. User will either get 1 of the following results.
- Entity A will contain the mapping b (from orm.xml) and mapping c and d (from eclipse-orm.xml), or
- Entity A will contain the mappings c and d (from eclipse-orm.xml) and mapping x (from some-other-mapping-file)

Use case 4

META-INF/orm.xml - defines Entity A with the mappings b and c.
META-INF/extensions/eclipse-orm.xml (note: This file is then added through a <mapping-file> tag in the persistence.xml) - defines defines Entity A with the mappings c and d.
Result - Ambiguous. Entity A will defined from orm.xml or /extensions/eclipse-orm.xml based on which files was read last.

Use case 5

META-INF/orm.xml - defines Entity A with the mappings b and c.
META-INF/jpa-mapping-file.xml - defines Entity A with the mappings a and d.
META-INF/extensions/eclipse-mapping-file.xml - defines defines Entity A with the mappings c and d.
Result - Ambiguous. Entity A will defined from orm.xml or jpa-mapping-file.xml or /extensions/eclipse-mapping-file.xml based on which files was read last.

File Granularity

Developers will be able to use the EclipseLink-ORM.XML file at the same granularity as a JPA ORM.XML. This means that within a persistence unit there can be zero or more files used.

Also, the EclipseLink-ORM.XML schema will relax the need to specify fully qualified classes. For those elements that require a class specification, the user may relax the qualifying of java lang classes (Byte, Double, Float, Integer, Long, Short, Boolean, Character, String etc ...)

EclipseLink-ORM.XML in place of JPA's ORM.XML

The EclipseLink runtime will support usage of EclipseLink-ORM.XML anywhere a JPA ORM.XML can be used. The runtime will automatically detect that the file is a native implementation and read and interpret its complete contents.

Note: It is important to document that this approach may introduce portability issues and that default EclipseLink naming or reference through a sessions configuration can also be used.

API access to EclipseLink-ORM.XML

The EclipseLink-ORM.XML file will be usable anywhere the previous deployment XML file can be used:

Through an XMLProjectReader.
- Loading multiple EclipseLink-ORM.XML files into a single project will require the use of a sessions.xml where the user may add additional projects.
- Alternatively, the user may load multiple files individually and call:
  - primaryProject.addDescriptors(additionalProject)
  - primaryProject.addDescriptors(additionalProject, session) // where a session is available.
Through SessionManager (XMLSessionConfigLoader) and SessionFactory

Note: When a EclipseLink-ORM.XML file is loaded (as a deployment XML file), any annotations defined on those classes from that XML file will be processed as well.

Backwards Compatibility

EclipseLink will support reading XML mapping files from Oracle TopLink 11 and 10.1.3. It will not be required to handle XML mapping files from early milestones of EclipseLink.

EclipseLink-ORM.XML Writing

The EclipseLink runtime currently supports writing out its deployment XML mapping file using MOXy. It is this support that the Workbench leverages to generate these files. As part of this feature the writing of XML mapping files must be enhanced.

When writing an EclipseLink project into XML the new EclipseLink-ORM.XML schema will be used for all object-relational projects.
- Since the implementation of supporting the new EclipseLink-ORM.XML schema will be done across several Milestones, the write-out of the object-relational projects using the new EclipseLink-ORM.XML schema should be an option to the user. Forcing them to the EclipseLink-ORM.XML schema before it is fully defined and supported will cause users to 'lose' mapping information from their projects.
- The Workbench will also need to populate a new configuration project model. It currently populates directly to an EclipseLink project.
- Default values should not be written.
When writing an EclipseLink project into XML the current deploymentXML schema will be used for native MOXy and EIS projects

Writing Open Issues:

Will the writing API be enhanced to support multiple file generation for custom granularity?
- The user can then select which descriptors to write to which files.
Will the writing API be enhanced to support writing out the common JPA ORM.XML content into standard ORM.XML file(s)?
- The user will in-turn get two files (or more based on the point above). One conforming to JPA's ORM.XML schema and the second containing all the EclipseLink extensions into an EclipseLink-ORM.XML file.

Functionality

The EclipseLink-ORM.XML schema will be built from the existing ORM.XML schema. That is, we will add new complex and simple elements to the schema.

The full functionality of EclipseLink and the existing native schema cannot be ported to the EclipseLink ORM.xml schema in one Milestone drop however. Will provide the new features throughout several Milestones. NOTE: These Milestones will only include XML support. That is, annotation support along with XML override and merge capability will be provideded at a later date. Nothing should be added to the schema unless its internal processing is implemented, therefore, ensuring our users have a fully supported schema at the end of every Milestone.

The following Milestones serve as an example of our work going forth. Notice the Milestone content and ordering may be re-worked based on further discussions and priorities. Each Milestone will deliver a design, implementation and testing of the Milestone content.

This section discusses the implementation phases of this project.

Milestone – a 30 day development cycle

Note:

At every Milestone, any remaining set of features not available through EclipseLink ORM.xml schema or annotations will remain available through the use of a session customizer.
NOTE: The Milestones below do not directly relate to an actual EclipseLink Milestone. Hence they will be labelled with a letter until such time that they are assigned to a specific Milestone.

Milestone a

Convert the existing JPA XML metadata processing from SAX parsing to use MOXy. This is necessary to align all XML metadata reading into the same framework and thus enable a consistent implementation and support overriding.

Milestone b

This milestone will provide XML metadata support for existing native EclipseLink annotations - Design Spec

Milestone c

Complex (PLSQL) type support for stored procedure parameters
Sequencing on non-id attributes.
attributes-complete - have a flag to indicate not to auto generate any unspecified attributes, this is important in XML when the class may continue to evolve.
primary-key element to allow giving columns, (allow one-to-one pks, or including other fields such as the inheritance indicator, field from embeddable, etc.)
allow target-join-column in a one-to-one (allows complex target foreign keys and one-to-one without mappedBy)

Milestone d

Transformation mappings
Aggregate-collection mapping
Variable 1-1 mapping
Serialized Converter
Class-instance converter

Milestone e

XML-type or data-type
Query-keys
Mapping custom-sql/calls
Custom-sql/calls
Mapping selection-criteria

Milestone f

Query sequence
Unary-table sequence
Copy-policy
Instantiation-policy

Milestone g

Additional join
Multiple table join
Multiple table foreign-keys
Inheritance-joins

Milestone h

Fetch groups
Class extractor
Additional events
Does exist
Default timeout
Interfaces
History

Milestone i

???

Milestone j

JPA 2.0 support

Also note that most metadata configurations from the JPA ORM.xml schema are optional. These optional components should continue within the EclipseLink ORM.xml schema wherever possible when adding new features. This will help maintain backwards compatibility and also avoid creating a new versioned schema for every new feature added and our users require little to hopefully no changes to their configurations.

Design Constraints

Expanding our feature set with the new ORM.xml schema will not proceed till our OX solution has been implemented. After that time, Milestones are free to be re-ordered or re-organized as necessary.

Maintainability

The maintainability of this project is greatly eased by updating our current JPA metadata processing to use our OX technology.

GUI

JPA comfigurations are supported through the Dali project. This project should be updated to support extended features made available from the new EclipseLink ORM.xml schema and annotations.

Config files

The Dali project should support writing out the EclipseLink ORM.xml file.

Any file that is read in using the 11 or 10.1.3 format should be have the option to be written out to the EclipseLink-ORM.XML schema format. Until the EclipseLink-ORM.XML schema supports the full feature set from the existing EclipseLink deployment XML schema, this will allow users to maintain all their mappings and configurations.

Documentation

Any documents that outline specific xml configurations should be listed here.

Open Issues

This section lists the open issues that are still pending that must be decided prior to fully implementing this project's requirements.

Issue #	Owner	Description / Notes
1	Group	Where do we draw the line on overlaying EclipseLink ORM based schema files over the existing JPA orm and mapping files?
2	Group	Will the writing API be enhanced to support multiple file generation for custom granularity?
3	Group	Will the writing API be enhanced to support writing out the common JPA ORM.XML content into standard ORM.XML file(s)?
4	Group	JPA + Oracle TopLink loading is currently not supported. That is, user's cannot load JPA against an existing Oracle TopLink server session, they are mutually exclusive. Do we want to introduce this functionality?
5	Group	Define candidate list of features that must be added during this process and file bugs for additional capabilities to be added later

Decisions

This section lists decisions made. These are intended to document the resolution of open issues or constraints added to the project that are important.

Issue #	Description / Notes	Decision
?	Description	Decision

Future Considerations

During the research for this project the following items were identified as out of scope but are captured here as potential future enhancements. If agreed upon during the review process these should be logged in the bug system.

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