Latest revision as of 14:37, 11 April 2008

Functional Specification: EclipseLink ORM XML

ER 200040

Document History

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:

1. 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.
2. 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).
3. Must embrace configuration by exception so only scope and non-default configurations need to be specified.
4. Must embrace minimal config, ORM.XML alignment for overrides, and complete configuration without any JPA annotations or XML.
5. 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.
6. 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 ORM.XML schema. Currently no elements as a whole are required only certain attributes within specified elements are required. Those elements and their requirements are as follows:

<entity-mappings>

<entity>, <entity-listener>, <id-class>, <embeddable>, <mapped-superclass>

<pre-persist>, <post-persist>, <pre-remove>, <post-remove>, <pre-update>, 
<post-update>, <post-load>

<query-hint>

<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>

<entity-result>

<field-result>

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:

1. 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).
2. Expand EclipseLink’s feature availability within the EclipseLink-ORM.XML beyond what is currently available.
   • See Functionality section below
3. 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

Note: JPA + Oracle TopLink loading is currently not supported and will not be added at this time.

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:

1. 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 that is specified in the persistence unit.

Override and Merging Rules

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 there 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. Therefore, after any extensions/overlays have been applied, this field will still be processed like any other mapping file.

Persistence Unit Metadata

Currently a persistence-unit-metadata specification is to be defined in one and only one mapping file and it 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

Entities, embeddables and mapped superclasses are defined within entity-mappings but are discussed in later sections. New entities, embeddables and mapped superclasses (that is solely defined in the EclipseLink-ORM.XML file) will be added to the persistence unit whereas otherwise will be merged and overridden as specified in their related sections below. The top level elements of the entity-mappings sections will be discussed here.

Mapped Superclass

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 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. Therefore, we will allow the merging of that classes metadata. The individual override rules for that metadata is tabled below.

Embeddable

An embeddable can be defined wholely or may be defined so as to provide extensions to an embeddeable from another mapping file. Therefore, we will allow the merging of that classes metadata. The individual override rules for that metadata is tabled below.

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

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

The writing will maintain its current functionality of writing to a single file only.

Functionality

The full functionality of EclipseLink and the existing native schema cannot be ported to the EclipseLink-ORM.XML schema in one Milestone drop. The full list of features will be provided across several Milestones. Each feature currently not supported by the EclipseLink-ORM.XML schema is (and should continue to be) entered as a bug. The bugs will then be addressed in later Milestones.

NOTE: Each bug (feature request) includes not only the XML support but the annotation support with the associated XML override and merging capabilities.

Nothing should be ever 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. At every Milestone, any remaining set of features not available through the EclipseLink-ORM.XML schema or annotations will remain available through the use of a session customizer.

The following bugs have been entered against the EclipseLink-ORM.XML schema.

Entity

These are Entity definition or Descriptor level configuration features.

211315: Copy Policy

The copy policy can be configured with one of the following approaches.

Instantiation Copy Policy

@InstantiationCopyPolicy

<instantiation-copy-policy/>

Custom Copy Policy

User provided class name implementing CopyPolicy

@CopyPolicy("foo.Bar")

<copy-policy policy-class="foo.Bar"/>

Clone Copy Policy

@CloneCopyPolicy(method="myClone")
 
@CloneCopyPolicy(method="myClone", workingCopyMethod="myWorkingCopyClone")
 
@CloneCopyPolicy(workingCopyMethod="myWorkingCopyClone")

<clone-copy-policy type="copy" method="myClone"
workingCopyMethod="myWorkingCopyClone"/>
 
<clone-copy-policy type="copy" workingCopyMethod="myWorkingCopyClone"/>
 
<clone-copy-policy type="copy" method="myClone"/>

Mappings

The following are the outstanding mapping bugs:

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.

211300: Transformation Mapping

@Transformation(fetch=FecthType.LAZY, optional="true")
@ReadTransformer(class=package.MyNormalHoursTransformer.class)
@WriteTranformers({
   @WriteTranformer(column=@Column(name="START_TIME"), 
      method="getStartDate"),
   @WriteTranformer(column=@Column(name="END_TIME"), 
      class=package.MyTimeTransformer.class)
})
@Mutable
@ReturnUpdate
@Access(AccessType.PROPERTY)
@AccessMethods(get="getNormalHours", set="setNormalHours")
@Properties({
   @Property(name="x", value="y")
})

And in XML:

<transformation name="normalHours" fetch="LAZY" optional="true">
     <read-transformer method="buildNormalHours"/>
     <write-transformer method="getStartTime">
             <column name="START_TIME"/>
     </write-transformer>
     <write-transformer class="package.MyTimeTransformer">
             <column name="END_TIME"/>
     </write-transformer>
     <mutable/>
     <return-update/>
     <access type="PROPERTY"/>
     <access-methods get="getNormalHours" set="setNormalHours"/>
     <properties>
        <property name="x" value="y"/>
     </properties>
</transformation>

211304: Class Instance Converter

Enables the configuration of ClassInstanceConverter which allows a class name, stored in the database, to be converter to and from a new instance of the specific class.

@Basic
@Convert("class-instance")
public AddressType getType(){
    return type;
}

<basic name="type">
    <convert>class-instance</convert>
</basic>

211302: Variable 1-1 Mapping

@VariableOneToOne(
    cascade={ALL},
    fetch=LAZY,
    discriminatorColumn=@DiscriminatorColumn(name="CONTACT_TYPE"),
    discriminatorClasses={
        @DiscriminatorClass(discriminator="E", value="Email.class"), 
        @DiscriminatorClass(discriminator="P", value="Phone.class")
    }
}
@JoinColumn(name="CONTACT_ID", referencedColumnName="C_ID")
@PrivateOwned
@JoinFetch(INNER)
public Contact getContact() {
    return contact;
}

<variable-one-to-one name="contact" fetch="LAZY">
    <cascade>
        <cascade-all/>
    </cascade>
    <discriminator-column name="CONTACT_TYPE"/>
    <discriminator-class discriminator="E" value="Email.class"/>
    <discriminator-class discriminator="P" value="Phone.class"/>
    <join-column name="CONTACT_ID" referenced-column-name="C_ID"/>
    <private-owned/>
    <join-fetch>INNER</join-fetch>
</variable-one-to-one>

Other Issues

The following bugs also affect the full completeness of this functionality.

Resolved Issues

The following bugs originally filed will be deferred from the 1.0 release or will not be addressed.

Open Issues

We need to verify that the following topics to ensure these are accessible as JPA extensions

• WrapperPolicy: EclipseLink-ORM.XML

Design Constraints

Expanding our feature set with the new ORM.xml schema will not proceed till our OX solution has been implemented. After that, functinality bugs may be processed and prioritized for implementation as deemed necessary.

Maintainability

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

GUI

JPA configurations 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.

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.

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.

• Enhance the file write-out capabilities.