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Talk:EclipseLink/UserGuide/JPA/Basic JPA Development/Mapping/Additional Criteria

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Revision as of 13:07, 21 April 2011 by Ben.gelernter.oracle.com (Talk | contribs)

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  • Documentation should be from JPA perspective, not native API, do not talk about descriptors, expressions etc., talk about Entities, Queries. [fixed - bg]
  • Merging and overriding applies to all annotations/xml, should not document it in here or in every page, but have a single page that documents the overriding behavior. [fixed - bg]
  • Examples are not use "source lang="java"/"xml"" tags. [fixed - bg]
  • The example formatting is off, two lines appended to one. The example should be relevant to something that a user would want to do, i.e. ."this.isDeleted = false", or effective dates, or tenants. [fixed - bg]
  • Should state the purpose of this feature, why would someone want to use it? Soft deletes, history, multi-tenancy, shared table [added -bg. But I need more information about how/why this feature is useful for those items]
  • Should include link to API (annotation, maybe native API (DescriptorQueryManager, Expression))[fixed - bg]
James.sutherland.oracle.com 19:33, 28 February 2011 (UTC)
  • AdditionalCriteria is more part of mapping, than querying, should probably be in the mapping section.
James.sutherland.oracle.com 16:52, 1 March 2011 (UTC)[fixed - bg]

Questions 4/4/11 BG Why is this useful for multi-tenancy, soft deletes, history, shared tables, and temporal filtering? Can someone provide examples, if you think that would be helpful?

The reason for AdditionalCriteria is to support parametrized views on the user's data.
Multi-tenancy is when you have the data for several applications/users/tenants in the same table. Each tenant only wants to see their own data.
To do this with AdditionalCriteria, you would define @AdditionalCriteria("TENANT = 'Billing'") if you were building an application just for billing that used shared data. Or, @AdditionalCriteria("this.tenant = :tenant") if you application could be used by multiple different tenants (at the same time). When the tenant acquired its EntityManagerFactory or EntityManager it would set the persistence/entity manager property "tenant" to their name.

i.e.

Map properties = new HashMap();
properties.put("tenant", "ACME");
EntityManagerFactory emf = Persistence.createEntityManagerFactory(properties);

or,

Map properties = new HashMap();
properties.put("tenant", "ACME");
EntityManager em = factory.createEntityManager(properties);
You might want to add a section on multi-tenancy and explain it in detail, then just reference if from here. We will have more multi-tenancy support in the 2.3 release.
A soft delete is when user do not ever delete any data, but just mark it as deleted, so the keep a record of it.
@AdditionalCriteria("this.isDeleted = false"), this will filter any delete data from any query.
Again you may wish to have a section on soft deletes and reference it (can also explain how to override the deleteSQL to update the flag)
History is when data is never removed or updated, on an update a new row is inserted with a new start/end time instead.
We have specific history support, but if the user just wants something simpler or more generic they can use criteria.
@AdditionalCriteria("this.endDate is null"), this will return the current data from any query
Or you could create an EntityManager on a specific date, @AdditionalCriteria("this.startDate <= :viewDate and this.endDate >= :viewDate")
For a shared table, you could have inheritance in the table, but not in the object model.
i.e. you have an SavingsAccount class and an ACCOUNT table but the ACCOUNT table also has checking account data that you want filtered.
James.sutherland.oracle.com 13:07, 5 April 2011 (UTC)