I was recently sponsored in a review of the ERXPartial package from ERExtensions by the very nice folks at
Logic Squad (
http://logicsquad.net/). They have authorized me to release everything into Wonder with the hope the ERXPartial package will be further developed and attract interest among the community.
For those who are unfamiliar with the partials package, the original package documentation from Mike Schrag contained this overview
Partial Entities provide a mechanism for defining a single entity whose definition spans across multiple EOModels along with tools to interact with these partial definitions in a type-safe way.
Partial entities are specifically designed to allow reuse and extension of existing models. A very common case where this becomes useful is that of a Person entity. Person is an entity that is used in many different scenarios, each of which requires additional attributes and relationships. For instance, you may have a task management application and you want to embed your calendaring framework into it. The common Person base entity may have "username" and "password" attributes, the tasking application may add an "activeTasks" relationship, and the calendaring framework may add a "scheduledEvents" relationship as well as "dayStartTime" and "dayEndTime" attributes. Note that partials are not designed to address the issue of "roles," where different people in the system may have different roles at different times. Partial entities are designed to address the issue of combining high level modules together to form more complex static entity declarations.
ERXPartials Test / Example
Notes about ERXPartials
Design Overview
ERXPartialBaseModel contains a very basic model containing the Root entity for the partials named Person.
- contains one standard relationship to GenderType
- contains a standard migration to create the initial tables for the Person and GenderType
- the migration also preloads some default values for gender and 100 semi-random Person records.
ERXPartialExampleModel contains additional extensions to the Person entity. The design uses two partial entities.
- one partial entity Partial_AuthenticatedPerson stores the basic authenticated user details username, password and lastLoginDate
- the second entity Partial_EmployeePerson stores common employee details like department, employeeType, salary and employeeNumber
- Company, Department and EmployeeType provide additional relationships for the Partial_EmployeePerson
- the migration in this frameworks creates the supporting tables in a normal fashion, and adds the additional attributes and constraints to the existing Person table.
ERXPartialExampleApp is a simple D2W demo application to demonstrate and test the Partials in a live environment.
Generated Partial entity Templates
By default I was using the _WonderEntity.java template, however there was a small issue with the generated content. When the template created a to-Many accessor method, it was using the relationship actual destination entity to generate the appropriate key path. However when the destination is a ERXPartial entity then the actual destination is the Root Entity. In this example the Department relationship to the Partial_EmployeePerson was generated as
Bad
public NSArray<er.example.erxpartials.model.Person> partial_EmployeePersons(EOQualifier qualifier, NSArray<EOSortOrdering> sortOrderings, boolean fetch) {
…
EOQualifier inverseQualifier = new EOKeyValueQualifier(er.example.erxpartials.model.Person.DEPARTMENT_KEY, EOQualifier.QualifierOperatorEqual, this);
Should be
public NSArray<er.example.erxpartials.model.Person> partial_EmployeePersons(EOQualifier qualifier, NSArray<EOSortOrdering> sortOrderings, boolean fetch) {
…
EOQualifier inverseQualifier = new EOKeyValueQualifier(er.example.erxpartials.model.Partial_EmployeePerson.DEPARTMENT_KEY, EOQualifier.QualifierOperatorEqual, this);
A patched _PartialWonderEntity.java is included int the Resources of the ERXPartialExampleModel project, but I think it needs to be moved into WOLips at some point.
Validation
The original behaviour for validation forwards all messages from the ERXPartial object to all contained partials. The problem is that only one of this partials will correctly validate the specified key path, the other partials will throw exceptions for unbound keys.
Additionally when the ERXPartialInitializer merges the partial entities into the Root, the EOEntities for the partials are removed from the EOModel, so it is not possible to query the original partial entity to determine if the key path is valid for that partial object.
My solution is currently to generate a static array for the attributes and the relationships and have theERXPartialGenericRecordquery the partial to determine the validity of a given key path before forwarding the invocation.
Patches for this are included in the ERXPartial, ERXPartialGenericObject classes and support is also added to the_PartialWonderEntity.java template.
Getting Started
create the database. I used Frontbase so the data model would have persistence and Frontbase specifically because it's what I use the most often (so it was the easiest to get up and running).
- Change into the ERXPartialBaseModel directory
GVCDev:ERXPartialBaseModel daspinall$ ant fb.recreate
Buildfile: /Volumes/Data/Development/GitHub/ERXPartials/wonder/Tests/ERXPartials/ERXPartialBaseModel/build.xml
init.properties:
fb.recreate: [exec] connect to ERXPartials user _system;
[exec] Cannot connect to ERXPartials@localhost
[exec] Database is not running
[exec] stop database;
[exec] No current session.
[exec] delete database ERXPartials;
[exec] Cannot delete database ERXPartials@localhost;
[exec] Reason: Database is unknown
[exec] create database ERXPartials;
[exec] connect to ERXPartials user _system;
[exec] Auto committing is on: SET COMMIT TRUE;
[exec] create user erxpartial;
[exec] set password test user erxpartial;
[exec] create schema erxpartial authorization erxpartial;
[exec] disconnect all;
[exec]
BUILD SUCCESSFUL
Total time: 1 second
GVCDev:ERXPartialBaseModel daspinall$
compile and run. The main page is a login page, but there is no login logic, just click the button :)
David Aspinall
Senior IT Consultant
Global Village Consulting Inc.