3-3-UpdatingEntities.md

3.3 Updating Entities

We had a look at Creating Entities in the last tutorial, know we want to have a look at update. As update we want to consider all operations that changes a property value. This is broader than the definition in OData, as it not only considers updates of entities, complex types, primitive types or the raw values , but also setting values to null via a delete requests.

To implement updates we have to override updateEntity. Again we do not look at validateChange. updateEntity has three parameter:

1. requestEntity is a container that provides access to data and information about a request. Form interest are:
   1. getEntityType, which provides an instance of JPAEntityType, which provides a bunch of information about the entity to be created. This starts with internal name of the JPA POJO and external name (name of OData entity) and ends with a list of attributes and keys.
   2. getData, which provides a map of attributes that are provided by the request. Keys of the map are the attribute names of the POJO. In case of complex/embedded attributes map is deep meaning the attribute is a map.
   3. getModifyUtil, which provides an instance of JPAModifyUtil, which contains of some helper methods.
   4. getKeys, which provides a map with the keys from the request.
2. em is an instance of EntityManager. A transaction has already been started, which is done to ensure the transactional integrity required for change sets within batch requests.
3. method contains the http method that was used.

For the tutorial we do not accept a PUT, which makes our live a little bit easier. To perform a PATCH or a DELETE setting values to null, the first step is to get the existing version of the entity. To do so we want to use the find method of the EntityManager, this requires to create an instance of the primary key. JPAModifyUtil provides with createPrimaryKey a helper method to support this. The method supports Id Classes having the corresponding setter as well as single keys. Next step is to insert the new values into the found instance. After that we can return an instance of JPAUpdateResult. JPAUpdateResult has two fields:

1. wasCreate, which indicates if a new instance was created if upsert is supported.
2. modifyedEntity, the changed (or in case of upsert the created) entity or a map of manipulated attributes.

Putting that together updateEntity can look as follows:

  @Override
  public JPAUpdateResult updateEntity(final JPARequestEntity requestEntity, final EntityManager em,
		final HttpMethod method) throws ODataJPAProcessException {
		
    if (method == HttpMethod.PATCH || method == HttpMethod.DELETE) {
      final Object instance = em.find(requestEntity.getEntityType().getTypeClass(), requestEntity.getModifyUtil()
          .createPrimaryKey(requestEntity.getEntityType(), requestEntity.getKeys(), requestEntity.getEntityType()));
      requestEntity.getModifyUtil().setAttributesDeep(requestEntity.getData(), instance, requestEntity.getEntityType());
      updateLinks(requestEntity, em, instance);
      return new JPAUpdateResult(false, instance);
    }
    return super.updateEntity(requestEntity, em, method);
  }

  private void updateLinks(final JPARequestEntity requestEntity, final EntityManager em, final Object instance)
      throws ODataJPAProcessorException, ODataJPAInvocationTargetException {
    if (requestEntity.getRelationLinks() != null) {
      for (Entry<JPAAssociationPath, List<JPARequestLink>> links : requestEntity.getRelationLinks().entrySet()) {
        for (JPARequestLink link : links.getValue()) {
          final Object related = em.find(link.getEntityType().getTypeClass(), requestEntity.getModifyUtil()
              .createPrimaryKey(link.getEntityType(), link.getRelatedKeys(), link.getEntityType()));
          requestEntity.getModifyUtil().linkEntities(instance, related, links.getKey());
        }
      }
    }
  }

To test the PATCH we can start with changing the instance we created during the last tutorial using the following request:

...Tutorial/Tutorial.svc/AdministrativeDivisions(DivisionCode='DE1',CodeID='NUTS1',CodePublisher='Eurostat')
{
        "AlternativeCode": "Test"
}

Now we have an AlternativeCode, which does not really make sense, so lets get ride of it again by the following DELETE request: .../Tutorial/Tutorial.svc/AdministrativeDivisions(DivisionCode='DE1',CodeID='NUTS1',CodePublisher='Eurostat')/AlternativeCode

We are also able to update relations between to entities. As a first step we create a new AdministrativeDivision:

...Tutorial/Tutorial.svc/AdministrativeDivisions
{
	"DivisionCode": "DE60",
	"CodeID": "NUTS2",
	"CodePublisher": "Eurostat",
	"CountryCode": "DEU"
}

Now we can link DE06 to its parent, make sure that the Parent association is update enabled, using a PATCH:

...Tutorial/Tutorial.svc/AdministrativeDivisions(DivisionCode='DE60',CodeID='NUTS2',CodePublisher='Eurostat')
{
  "@odata.type":"#Tutorial.AdministrativeDivision",
  "Parent@odata.bind": 
    "/AdministrativeDivisions(DivisionCode='DE6',CodeID='NUTS1',CodePublisher='Eurostat')"
}

Next we want to be bale to delete an entity: Tutorial 3.4 Deleting Entities