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3.6 Batch Requests

In the last tutorial we want to have a look at batch request and want to learn more about method validateChanges, which we have neglected up to now.

Again a set of additional AdministrativeDivisions shall be created, but instead of using a Deep Insert, as in the last tutorial, we want to us the following batch request:

URL: .../Tutorial/Tutorial.svc/$batch Header:

  • Content-Type: multipart/mixed;boundary=abc
  • Prefer: return=minimal

Body:

--abc
Content-Type: multipart/mixed; boundary=xyz


--xyz
Content-Type: application/http
Content-Transfer-Encoding: binary
Content-Id: 1
Prefer: return=minimal

POST AdministrativeDivisions HTTP/1.1
Accept: application/json
Content-Type: application/json

{
	"DivisionCode": "DE600",
	"CodeID": "NUTS3",
	"CodePublisher": "Eurostat",
	"CountryCode": "DEU",
	"Parent@odata.bind": "AdministrativeDivisions(DivisionCode='DE60',CodeID='NUTS2',CodePublisher='Eurostat')"
}

--xyz
Content-Type: application/http
Content-Transfer-Encoding: binary
Content-Id: 2
Prefer: return=minimal

POST AdministrativeDivisions HTTP/1.1
Accept: application/json
Content-Type: application/json

{
	"DivisionCode": "DE60",
	"CodeID": "NUTS2",
	"CodePublisher": "Eurostat",
	"CountryCode": "DEU",
	"Parent@odata.bind": "AdministrativeDivisions(DivisionCode='DE6',CodeID='NUTS1',CodePublisher='Eurostat')"
}

--xyz
Content-Type: application/http
Content-Transfer-Encoding: binary
Content-Id: 3
Prefer: return=minimal

POST AdministrativeDivisions HTTP/1.1
Accept: application/json
Content-Type: application/json

{
	"DivisionCode": "DE6",
	"CodeID": "NUTS1",
	"CodePublisher": "Eurostat",
	"CountryCode": "DEU"
}

--xyz--
--abc--

By purpose the order of the AdministrativeDivisions is from bottom to top, so the links point to entities that do not exist when a AdministrativeDivision is created. As a consequence we would get an error if we now execute the request. A response may look like this:

--batch_7b9f8232-e51d-46b3-8b3d-74d06b02477b
Content-Type: application/http
Content-Transfer-Encoding: binary

HTTP/1.1 500 Internal Server Error
OData-Version: 4.0
Content-Type: application/json;odata.metadata=minimal
Content-Length: 158

{"error":{"code":null,"message":"while trying to invoke the method java.lang.Object.getClass() of a null object loaded from local variable 'targetInstance'"}}
--batch_7b9f8232-e51d-46b3-8b3d-74d06b02477b--

The processing of the request aborts, as the link can not be created. To solve the problem we need to implement, as mentioned, validateChanges and create the links there. To be able to do so, we have to buffer the entities to process. The buffer shall be called entityBuffer and will be created within the constructor:

private final Map<Object, JPARequestEntity> entityBuffer;

public CUDRequestHandler() {
  entityBuffer = new HashMap<Object, JPARequestEntity>();
}

When ever an entity was changed we need to put it into the buffer. As an example this is done at createOneEntity:

private Object createOneEntity(final JPARequestEntity requestEntity, final EntityManager em)
    throws ODataJPAProcessorException {
  final Object instance = createInstance(getConstructor(requestEntity.getEntityType()));
  requestEntity.getModifyUtil().setAttributesDeep(requestEntity.getData(), instance);
  em.persist(instance);
  entityBuffer.put(instance, requestEntity);
  return instance;
}

Having done that we can implement validateChanges:

@Override
public void validateChanges(EntityManager em) throws ODataJPAProcessException {
  for (Entry<Object, JPARequestEntity> entity : entityBuffer.entrySet()) {
    processBindingLinks(entity.getValue().getRelationLinks(), entity.getKey(), entity.getValue().getModifyUtil(), em);
  }
}

And remove the call of processBindingLinks from createEntity:

@Override
public Object createEntity(final JPARequestEntity requestEntity, final EntityManager em)
    throws ODataJPAProcessException {

  final Object instance = createOneEntity(requestEntity, em);
  processRelatedEntities(requestEntity.getRelatedEntities(), requestEntity, instance, requestEntity.getModifyUtil(),
      em);
  return instance;
}

If now the request is rerun, we get a success response:

--batch_cdfc9535-29e1-4b91-9bb0-f851cf4248a4
Content-Type: multipart/mixed; boundary=changeset_7831e243-f658-48e1-bbdd-efbc4209d5ec

--changeset_7831e243-f658-48e1-bbdd-efbc4209d5ec
Content-Type: application/http
Content-Transfer-Encoding: binary
Content-ID: 1

HTTP/1.1 201 Created
OData-Version: 4.0
Content-Type: application/json;odata.metadata=minimal
Location: <Host:Port>/Tutorial/Tutorial.svc/AdministrativeDivisions(DivisionCode='DE600',CodeID='NUTS3',CodePublisher='Eurostat')
Content-Length: 240
...

Beside the linkage of entities the purpose of validateChanges is to give the opportunity to check the state of an entity in the context of other changed entities. E.g. you want to ensure that the certain value does not exceeds a limit or range given by another entity, but your should be able to change both with the same request.

Since OData version 3 an insert request has to contain a Content-Id. Up to now we had not utilized it. The following example should give a hint how to use it:

--abc
Content-Type: multipart/mixed; boundary=xyz


--xyz
Content-Type: application/http
Content-Transfer-Encoding: binary
Content-Id: 1
Prefer: return=minimal

POST AdministrativeDivisions HTTP/1.1
Accept: application/json
Content-Type: application/json

{
	"DivisionCode": "DEF",
	"CodeID": "NUTS1",
	"CodePublisher": "Eurostat",
	"CountryCode": "DEU"
}

--xyz
Content-Type: application/http
Content-Transfer-Encoding: binary
Content-Id: 2
Prefer: return=minimal

POST $1/Children HTTP/1.1
Accept: application/json
Content-Type: application/json

{
	"DivisionCode": "DEF0",
	"CodeID": "NUTS2",
	"CodePublisher": "Eurostat",
	"CountryCode": "DEU"
}

--xyz
Content-Type: application/http
Content-Transfer-Encoding: binary
Content-Id: 3
Prefer: return=minimal

POST $2/Children HTTP/1.1
Accept: application/json
Content-Type: application/json

{
	"DivisionCode": "DEF0B",
	"CodeID": "NUTS3",
	"CodePublisher": "Eurostat",
	"CountryCode": "DEU"
}
--xyz--
--abc--

In this example we start with top down, so the first entity that is created is the parent of the next. The later on is created via a link. Nevertheless the POST is executed on AdministrativeDivisions(DivisionCode='DEF',CodeID='NUTS1',CodePublisher='Eurostat'), but it does not contain any properties of it. As a consequence when method createEntity is called requestEntity.jpaAttributes is empty, whereas requestEntity.jpaKeys is filled. To be able to handle such requests we have to touch createEntity again. In case the key of an entity is provided we won't create it, but read it from the database or from the buffer:

@Override
public Object createEntity(final JPARequestEntity requestEntity, final EntityManager em)
		throws ODataJPAProcessException {

	Object instance = null;

	if (requestEntity.getKeys().isEmpty()) {
		// POST an Entity
		instance = createOneEntity(requestEntity, em);
	} else {
		// POST on Link only
		instance = findEntity(requestEntity, em);
	}
	processRelatedEntities(requestEntity.getRelatedEntities(), instance, requestEntity.getModifyUtil(), em);
	return instance;
}

A small helper method shall return an existing entity:

private Object findEntity(final JPARequestEntity requestEntity, EntityManager em) throws ODataJPAProcessorException,
		ODataJPAInvocationTargetException {

	final Object key = requestEntity.getModifyUtil().createPrimaryKey(requestEntity.getEntityType(), requestEntity
			.getKeys(), requestEntity.getEntityType());
	return em.find(requestEntity.getEntityType().getTypeClass(), key);
}

Please note that error handling has been skipped and that the interface of method processRelatedEntities has refactored.

After we have executed the batch POST request, we can check if everthing went well with the following GET request: .../Tutorial/Tutorial.svc/AdministrativeDivisions?$filter=contains(DivisionCode, 'DEF')&$expand=Parent