OData 4.0 Services (CRUD) using Olingo(JSON supported): Part-1

[Former Member]

1) Import the following  jars for OLINGO

odata-commons-api-4.0.0.jar

odata-commons-core-4.0.0.jar

odata-server-core-4.0.0.jar

slf4j-api-1.7.11.jar

commons-codec-1.9.jar

slf4j-simple-1.7.7.jar

jackson-dataformat-xml-2.4.2.jar

jackson-databind-2.4.2.jar

odata-server-api-4.0.0.jar

jackson-annotations-2.4.2.jar

antlr4-runtime-4.5.jar

stax2-api-3.1.4.jar

org.abego.treelayout.core-1.0.1.jar

jackson-module-jaxb-annotations-2.4.2.jar

commons.lang3-3.3.2.jar

jackson-core-2.4.2.jar

aalto-xml-0.9.10.jar

2) Create Provider that extends CsdlAbstractEdmProvider

1. 1.Define Namespace, Container, EntityType names, EntitySet names.
2. a. DEFINING NAMESPACE :
3. 
   

public static final String NAMESPACE = "OData.Demo";

1. b. DEFINING CONTAINER :

public static final String CONTAINER_NAME = "Container";

public static final FullQualifiedName CONTAINER = new FullQualifiedName(NAMESPACE, CONTAINER_NAME);

1. c. DEFINING ENTITY TYPE NAMES :

public static final String ET_STUDENT_NAME = "Student";

public static final FullQualifiedName ET_STUDENT_FQN = new FullQualifiedName (NAMESPACE, ET_STUDENT_NAME);

public static final String ET_SCHOOL_NAME = "School";

public static final FullQualifiedName ET_SCHOOL_FQN =FullQualifiedName(NAMESPACE, ET_SCHOOL_NAME);

1. d. DEFINING ENTITY SETS :

public static final String ES_STUDENTS_NAME = "Students";

public static final String ES_SCHOOLS_NAME = "Schools";

1. e. DEFINING NAVIGATIONS:

public static final String NAV_TO_SCHOOL = "School";

public static final String NAV_TO_STUDENTS = "Students";

1. 2. Override getEntityType, getEntitySet, getEntityContainerInfo, getEntityContainer, getSchemas methods .
2. a. OVERRIDING getEntityType:

@Override

  public CsdlEntityType getEntityType(FullQualifiedName entityTypeName) {

    // this method is called for each EntityType that are configured in the Schema

    CsdlEntityType entityType = null;

    if (entityTypeName.equals(ET_STUDENT_FQN)) {

      // create EntityType properties

      CsdlProperty stu_id = new CsdlProperty().setName("stu_id")

          .setType(EdmPrimitiveTypeKind.Int32.getFullQualifiedName());

      CsdlProperty stu_name = new CsdlProperty().setName("stu_name")

          .setType(EdmPrimitiveTypeKind.String.getFullQualifiedName());

      // create PropertyRef for Key element

      CsdlPropertyRef propertyRef = new CsdlPropertyRef();

      propertyRef.setName("stu_id");

      // navigation property: many-to-one, null not allowed (student must have a school)

      CsdlNavigationProperty navProp = new CsdlNavigationProperty().setName(NAV_TO_SCHOOL)

          .setType(ET_SCHOOL_FQN).setNullable(false).setPartner("Students");

      //add all the navigation properties to a list

      List<CsdlNavigationProperty> navPropList = new ArrayList<CsdlNavigationProperty>();

      navPropList.add(navProp);

      // configure EntityType

      entityType = new CsdlEntityType();

      entityType.setName(ET_STUDENT_NAME);

      entityType.setProperties(Arrays.asList(stu_id, stu_name));

      entityType.setKey(Arrays.asList(propertyRef));

      entityType.setNavigationProperties(navPropList);

    } else if (entityTypeName.equals(ET_SCHOOL_FQN)) {

      // create EntityType properties

      CsdlProperty school_id = new CsdlProperty().setName("school_id")

          .setType(EdmPrimitiveTypeKind.Int32.getFullQualifiedName());

      CsdlProperty school_name = new CsdlProperty().setName("school_name")

          .setType(EdmPrimitiveTypeKind.String.getFullQualifiedName());

      // create PropertyRef for Key element

      CsdlPropertyRef propertyRef = new CsdlPropertyRef();

      propertyRef.setName("school_name");

      // navigation property: one-to-many(a school can have many students)

      CsdlNavigationProperty navProp = new CsdlNavigationProperty().setName(NAV_TO_STUDENTS)

          .setType(ET_STUDENT_FQN).setCollection(true).setPartner("School");

\

      //add all navigation properties to a list

      List<CsdlNavigationProperty> navPropList = new ArrayList<CsdlNavigationProperty>();

      navPropList.add(navProp);

      // configure EntityType

      entityType = new CsdlEntityType();

      entityType.setName(ET_SCHOOL_NAME);

      entityType.setProperties(Arrays.asList(school_id, school_name));

      entityType.setKey(Arrays.asList(propertyRef));

      entityType.setNavigationProperties(navPropList);

    }

    return entityType;

  }

1. b. OVERRIDING getEntitySets:

@Override

  public CsdlEntitySet getEntitySet(FullQualifiedName entityContainer, String entitySetName) {

    CsdlEntitySet entitySet = null;

    if (entityContainer.equals(CONTAINER)) {

      if (entitySetName.equals(ES_STUDENTS_NAME)) {

        entitySet = new CsdlEntitySet();

        entitySet.setName(ES_STUDENTS_NAME);

        entitySet.setType(ET_STUDENT_FQN);

        // navigation

        CsdlNavigationPropertyBinding navPropBinding = new CsdlNavigationPropertyBinding();

        navPropBinding.setTarget("Schools"); // the target entity set, where the navigation property points to

        navPropBinding.setPath("School"); // the path from entity type to navigation property

        //add all navigation property bindings to a list

List<CsdlNavigationPropertyBinding> navPropBindingList = new ArrayList<CsdlNavigationPropertyBinding>();

        navPropBindingList.add(navPropBinding);

        entitySet.setNavigationPropertyBindings(navPropBindingList);

      } else if (entitySetName.equals(ES_SCHOOLS_NAME)) {

        entitySet = new CsdlEntitySet();

        entitySet.setName(ES_SCHOOLS_NAME);

        entitySet.setType(ET_SCHOOL_FQN);

        // navigation

        CsdlNavigationPropertyBinding navPropBinding = new CsdlNavigationPropertyBinding();

        navPropBinding.setTarget("Students"); // the target entity set, where the navigation property points to

        navPropBinding.setPath("Students"); // the path from entity type to navigation property

      //add all navigation property bindings to a list

List<CsdlNavigationPropertyBinding> navPropBindingList = new ArrayList<CsdlNavigationPropertyBinding>();

        navPropBindingList.add(navPropBinding);

        entitySet.setNavigationPropertyBindings(navPropBindingList);

      }

    }

    return entitySet;

  }

1. c. OVERRIDING getEntityContainerInfo

@Override

  public CsdlEntityContainerInfo getEntityContainerInfo(FullQualifiedName entityContainerName) {

    // This method is invoked when displaying the service document at

    // eg: http://localhost:8088/school_stu_teachers/DemoService.svc/

    if (entityContainerName == null || entityContainerName.equals(CONTAINER)) {

      CsdlEntityContainerInfo entityContainerInfo = new CsdlEntityContainerInfo();

      entityContainerInfo.setContainerName(CONTAINER);

      return entityContainerInfo;

    }

    return null;

  }

1. d. OVERRIDING getSchemas

@Override

  public List<CsdlSchema> getSchemas() {

    // create Schema and set the namespace to schema

    CsdlSchema schema = new CsdlSchema();

    schema.setNamespace(NAMESPACE);

    // add EntityTypes

    List<CsdlEntityType> entityTypes = new ArrayList<CsdlEntityType>();

    entityTypes.add(getEntityType(ET_STUDENT_FQN));

    entityTypes.add(getEntityType(ET_SCHOOL_FQN));

    schema.setEntityTypes(entityTypes);

    // add EntityContainer

    schema.setEntityContainer(getEntityContainer());

    // finally add current schema to the list of schemas

    List<CsdlSchema> schemas = new ArrayList<CsdlSchema>();

    schemas.add(schema);

    return schemas;

  }

1. e. DEFINING getEntityContainer

@Override

  public CsdlEntityContainer getEntityContainer() {

    // create EntitySets

    List<CsdlEntitySet> entitySets = new ArrayList<CsdlEntitySet>();

    entitySets.add(getEntitySet(CONTAINER, ES_STUDENTS_NAME));

    entitySets.add(getEntitySet(CONTAINER, ES_SCHOOLS_NAME));

    // create EntityContainer

    CsdlEntityContainer entityContainer = new CsdlEntityContainer();

    entityContainer.setName(CONTAINER_NAME);

    entityContainer.setEntitySets(entitySets);

    return entityContainer;

  }

}

Metadata:

3)Create processor (for Entity) that implements Entityprocessor:

1. a. Create readEntity method that gets called on ‘GET’ request

/**

        * This method is invoked when a single entity has to be read. In our

        * example, this can be either a "normal" read operation, or a navigation:

        *

        * Example for "normal" read operation:

        * http://localhost:8080/school_stu_teachers/DemoService.svc/Students(1)

        *

        * Example for navigation

        * http://localhost:8080/school_stu_teachers/DemoService.svc/Students(1)/School

*/

public void readEntity(ODataRequest request, ODataResponse response,UriInfo uriInfo, ContentType responseFormat)throws ODataApplicationException, SerializerException {

       EdmEntityType responseEdmEntityType = null; // we'll need this to build

                                                                                          //the ContextURL

       Entity responseEntity = new Entity(); // required for serialization of the response body

       EdmEntitySet responseEdmEntitySet = null; // we need this for building

              // 1st step: retrieve the requested Entity: can be "normal" read

              // operation, or navigation (to-one)

       List<UriResource> resourceParts = uriInfo.getUriResourceParts();

       int segmentCount = resourceParts.size();

       UriResource uriResource = resourceParts.get(0); // in our example, the

                                                                                                // first segment is the

                                                                                                // EntitySet

       if (!(uriResource instanceof UriResourceEntitySet)) {

              throw new ODataApplicationException("Only EntitySet is supported",

                                  HttpStatusCode.NOT_IMPLEMENTED.getStatusCode(),

                                  Locale.ENGLISH);

              }

       UriResourceEntitySet uriResourceEntitySet = (UriResourceEntitySet) uriResource;

       EdmEntitySet startEdmEntitySet = uriResourceEntitySet.getEntitySet();

              // Analyze the URI segments

       if (segmentCount == 1) {

              // no navigation

       responseEdmEntityType = startEdmEntitySet.getEntityType();

       responseEdmEntitySet = startEdmEntitySet; // since we have only one

                                                                                                                     //http://localhost:8088/school_stu_teachers/DemoService.svc/Schools('psg')

                        if(responseEdmEntityType.getName().equals(DemoEdmProvider.ET_SCHOOL_NAME))

                        {

List<UriParameter> keyPredicates = uriResourceEntitySet.getKeyPredicates();

//get the school entity that has name psg

                                  responseEntity=storage.readEntityDataFromDatabase(responseEdmEntitySet,keyPredicates);

                        }

       } else if (segmentCount == 2) {

                     //eg..Students(1)/School

       System.out.println("segment count 2");

                     // navigation

       UriResource navSegment = resourceParts.get(1); //so gets school entity set

       if (navSegment instanceof UriResourceNavigation) {

       UriResourceNavigation uriResourceNavigation = (UriResourceNavigation) navSegment;

       EdmNavigationProperty edmNavigationProperty = uriResourceNavigation.getProperty();

       responseEdmEntityType = edmNavigationProperty.getType();

                           // contextURL displays the last segment

                           //System.out.println(""+startEdmEntitySet.getEntityType());

       responseEdmEntitySet = Util.getNavigationTargetEntitySet(

                                         startEdmEntitySet, edmNavigationProperty);

       List<UriParameter> keyPredicates = uriResourceEntitySet.getKeyPredicates();

                           // fetch the data from backend.

                           // e.g. for Students(1)/School we have to find first  Students(1)

                           Entity sourceEntity = storage.readEntityData(startEdmEntitySet,keyPredicates);

                           // now we have to check if the navigation is

                           // a) to-one: e.g. Students(1)/School

                           // b) to-many with key: e.g. Schools('psg')/Students(5)

                           // the key for nav is used in this case:

                           // Schools('psg')/Students(5)

List<UriParameter> navKeyPredicates = uriResourceNavigation.getKeyPredicates();

if (navKeyPredicates.isEmpty()) { // e.g. DemoService.svc/Students(1)/School

responseEntity = storage.getRelatedEntity(sourceEntity,

                                                responseEdmEntityType);

} else { // e.g. DemoService.svc/Schools(3)/Students(5)

                                                                     responseEntity = storage.getRelatedEntity(sourceEntity,

                                                responseEdmEntityType, navKeyPredicates);

                           }

                     }

              } else {

                     // this would be the case for e.g.

                     // Students(1)/School/Students(1)/School

                     throw new ODataApplicationException("Not supported",

                                  HttpStatusCode.NOT_IMPLEMENTED.getStatusCode(), Locale.ROOT);

              }

              if (responseEntity == null) {

                     // this is the case for e.g. DemoService.svc/Schools('psg') or

                     // DemoService.svc/Schools('psg')/Students(999) where student with id 999 not exists

                     throw new ODataApplicationException("Nothing found.",

                                  HttpStatusCode.NOT_FOUND.getStatusCode(), Locale.ROOT);

              }

              SelectOption selectOption = uriInfo.getSelectOption();

              ExpandOption expandOption = uriInfo.getExpandOption();

              // in our example: http://localhost:8080/school_stu_teachers/DemoService.svc/Schools('psg')/$expand=Students

              // or http://localhost:8080/school_stu_teachers/DemoService.svc/Students(1)?$expand=Schools

              if(expandOption != null) {

                     //since more than 1 expand option eg. students,teachers

                     for(int i=0;i<expandOption.getExpandItems().size();i++)

                     {

                     // retrieve the EdmNavigationProperty from the expand expression

                     // Note: in our example, we have only one NavigationProperty, so we can directly access it

                     EdmNavigationProperty edmNavigationProperty = null;

                     ExpandItem expandItem = expandOption.getExpandItems().get(i);

                     if(expandItem.isStar()) {

                           List<EdmNavigationPropertyBinding> bindings = responseEdmEntitySet.getNavigationPropertyBindings();

                           // we know that there are navigation bindings

                           // however normally in this case a check if navigation bindings exists is done

                           if(!bindings.isEmpty()) {

                                  //since we have more than 1 nav bindings

                                  EdmNavigationPropertyBinding binding = bindings.get(i);

                                  EdmElement property = responseEdmEntitySet.getEntityType().getProperty(binding.getPath());

                                  // we don't need to handle error cases, as it is done in the Olingo library

                                  if(property instanceof EdmNavigationProperty) {

                                         edmNavigationProperty = (EdmNavigationProperty) property;

                                  }

                           }

                     } else {

                           // can be 'School' or 'Students', no path supported

                           UriResource expandUriResource = expandItem.getResourcePath().getUriResourceParts().get(0);

                           // we don't need to handle error cases, as it is done in the Olingo library

                           if(expandUriResource instanceof UriResourceNavigation) {

                                  edmNavigationProperty = ((UriResourceNavigation) expandUriResource).getProperty();

                           }

                     }

                     // can be 'School' or 'Students', no path supported

                     // we don't need to handle error cases, as it is done in the Olingo library

                     if(edmNavigationProperty != null) {

                           EdmEntityType expandEdmEntityType = edmNavigationProperty.getType();

                           String navPropName = edmNavigationProperty.getName();

                           // build the inline data

                           Link link = new Link();

                           link.setTitle(navPropName);

                           link.setType(Constants.ENTITY_NAVIGATION_LINK_TYPE);

        link.setRel(Constants.NS_ASSOCIATION_LINK_REL + navPropName);

                           if(edmNavigationProperty.isCollection()) { // in case of Schools('psg')/$expand=Students

                                  // fetch the data for the $expand (to-many navigation) from backend

                                  // here we get the data for the expand

                                  System.out.println("iscollection");

                                  //get students of given school

                                  EntityCollection expandEntityCollection =

              storage.getRelatedEntityCollection(responseEntity, expandEdmEntityType);

                                  link.setInlineEntitySet(expandEntityCollection);

          link.setHref(expandEntityCollection.getId().toASCIIString());

                           } else {  // in case of Students(1)?$expand=School

                                  // fetch the data for the $expand (to-one navigation) from backend

                                  // here we get the data for the expand

                                  //get school of given student

                                  Entity expandEntity = storage.getRelatedEntity(responseEntity, expandEdmEntityType);

                                  link.setInlineEntity(expandEntity);

          link.setHref(expandEntity.getId().toASCIIString());

                           }

                           // set the link - containing the expanded data - to the current entity

                           responseEntity.getNavigationLinks().add(link);

                     }

              }

                           // 3. serialize

              EdmEntityType edmEntityType = responseEdmEntitySet.getEntityType();

              // we need the property names of the $select, in order to build the context URL

              String selectList = odata.createUriHelper().buildContextURLSelectList(edmEntityType, expandOption, selectOption);

              ContextURL contextUrl = ContextURL.with().entitySet(responseEdmEntitySet)

                                         .selectList(selectList)

                                         .suffix(Suffix.ENTITY).build();

              // make sure that $expand and $select are considered by the serializer

              // adding the selectOption to the serializerOpts will actually tell the lib to do the job

              EntitySerializerOptions opts = EntitySerializerOptions.with()

                                         .contextURL(contextUrl)

                                         .select(selectOption)

                                         .expand(expandOption)

                                         .build();

              ODataSerializer serializer = this.odata.createSerializer(responseFormat);

              SerializerResult serializerResult = serializer.entity(srvMetadata, edmEntityType, responseEntity, opts);

              // 5. configure the response object

              response.setContent(serializerResult.getContent());

              response.setStatusCode(HttpStatusCode.OK.getStatusCode());

              response.setHeader(HttpHeader.CONTENT_TYPE, responseFormat.toContentTypeString());

       }

       //if expand null

              else{

              ContextURL contextUrl =

                            ContextURL.with().entitySet(responseEdmEntitySet).suffix(Suffix.ENTITY).build();

                            EntitySerializerOptions opts =

                            EntitySerializerOptions.with().contextURL(contextUrl).build();

                            ODataSerializer serializer =

                            this.odata.createSerializer(responseFormat);

                            SerializerResult serializerResult =

                            serializer.entity(this.srvMetadata,

                            responseEdmEntityType, responseEntity, opts);

                            // 4. configure the response object

                            response.setContent(serializerResult.getContent());

                            response.setStatusCode(HttpStatusCode.OK.getStatusCode());

                            response.setHeader(HttpHeader.CONTENT_TYPE,

                            responseFormat.toContentTypeString());}

       }

1. b. Create createEntity method that gets called on ‘POST’ request:

public void createEntity(ODataRequest request, ODataResponse response,

                     UriInfo uriInfo, ContentType requestFormat,

                     ContentType responseFormat) throws ODataApplicationException,

                     DeserializerException, SerializerException {

              List<StudentDto> studList=new ArrayList<StudentDto>();

       EdmEntityType responseEdmEntityType = null; // we'll need this to build

                                                                                         // response body

       EdmEntitySet responseEdmEntitySet = null; // we need this for building

                                                                                         // the contextUrl

              // 1st step: retrieve the requested Entity: can be "normal" read

              // operation, or navigation (to-one)

       List<UriResource> resourceParts = uriInfo.getUriResourceParts();

       int segmentCount = resourceParts.size();

       UriResource uriResource = resourceParts.get(0); // in our example, the

first segment is the EntitySet

              if (!(uriResource instanceof UriResourceEntitySet)) {

                     throw new ODataApplicationException("Only EntitySet is supported",

                                  HttpStatusCode.NOT_IMPLEMENTED.getStatusCode(),

                                  Locale.ENGLISH);

              }

              UriResourceEntitySet uriResourceEntitySet = (UriResourceEntitySet) uriResource;

              EdmEntitySet startEdmEntitySet = uriResourceEntitySet.getEntitySet();

              // Analyze the URI segments

              if (segmentCount == 1) { // no navigation

                     responseEdmEntityType = startEdmEntitySet.getEntityType();

                     responseEdmEntitySet = startEdmEntitySet; // since we have only one

if (responseEdmEntityType.getName().equals(DemoEdmProvider.ET_STUDENT_NAME))

                      {

                            EntityCollection ec=new EntityCollection();

                                  //get data(body)  from post

                                  InputStream requestInputStream = request.getBody();

                                  InputStream is = null;

                                  try {

                                         ObjectMapper mapper = new ObjectMapper();

                                  //     convert inputstream to json

                                         List<Map<String, Object>> jsonmap = mapper.readValue(

                                                       requestInputStream,

                                                       new TypeReference<List<Map<String, Object>>>() {

                                                       });

for (Map<String, Object> a : jsonmap) {

       SchoolDto s=new SchoolDto();

       SchoolDo d=new SchoolDo();

       List<Map<String, Object>> stdo=new ArrayList<Map<String, Object>>();

       Map<String, Object> b=new HashMap<String, Object>();

                                  String school_name=(String) a.get("school_name");

                                  s=dao.readSchoolData(school_name);

                                  d=s.getEntity(s);

                                   System.out.println(a.get("studentsDto"));

              stdo= (List<Map<String, Object>>) a.get("studentsDto");

                                  System.out.println(stdo.size());

                                  for(Map<String, Object> i:stdo)

                                  {

                                          StudentDto stuDto=new StudentDto();

                                          ServiceDao dao = new ServiceDao();

                                          StudentDo stuDo=new StudentDo();

                           b.put("stu_name", i.get("stu_name"));   

                           String mapAsJson = new ObjectMapper().writeValueAsString(b);

                                  //Converting json string to java object

                                   StudentDto stud= (StudentDto) fromJson(mapAsJson);

                                   //get studentdo from dto

                                   stuDo=stuDto.getEntity(stud);

                                   stuDo.setSchoolIdRef(d);

                                   dao.create(stuDo);

                                  }

                                  }

                                  }

                                  catch(Exception e)

                                  {System.out.println(e.getMessage());}

                     // 4. configure the response object

              //     response.setContent(serializedResponse.getContent());

                     response.setStatusCode(HttpStatusCode.CREATED.getStatusCode());

                     response.setHeader(HttpHeader.CONTENT_TYPE,

                                  responseFormat.toContentTypeString());

                      }

                      else if(responseEdmEntityType.getName().equals(DemoEdmProvider.ET_SCHOOL_NAME))

                      {

                     InputStream requestInputStream = request.getBody();

                     try {

                           ObjectMapper mapper = new ObjectMapper();

                     //read data (body of post) and convert it to list of maps

                           List<Map<String, Object>> jsonmap = mapper.readValue(

                                         requestInputStream,

                     new TypeReference<List<Map<String, Object>>>() {

                                         });

Map<String, Object> b=new HashMap<String, Object>();

for (Map<String, Object> a : jsonmap) {

                                  // Set<String> b = a.keySet();

                                  for (String i : a.keySet()) {

                                         System.out.println("key " + i + " value " + a.get(i));

                                  }

                                  b.put("school_id", a.get("school_id"));

                                  b.put("schoolName", a.get("school_name"));

                                  b.put("studentsDto", a.get("studentsDto"));

                                  b.put("teachersDto", a.get("teachersDto"));

                                  String mapAsJson = new ObjectMapper().writeValueAsString(b);

                                  //Converting json string to java object

                                   SchoolDto scho= (SchoolDto) fromJson1(mapAsJson);

                                   //create an object in DB

                                   SchoolDto schoolDto=new SchoolDto();

                                   SchoolServiceDao dao = new SchoolServiceDao();

                                   SchoolDo schoolDo=new SchoolDo();

                                   List<SchoolDo> schoolDoList =new ArrayList<SchoolDo>();

                                   //get schooldo from dto

                                   schoolDo=schoolDto.getEntity(scho);

                                   schoolDoList.add(schoolDo);

                                  try {

                                         System.out.println(mapAsJson);

                                  } catch (Exception e) {

                                         System.out.println("Exception:"+e.getMessage());

                                  }

                                  System.out.println("hao");

                                  dao.create(schoolDoList);

                           }

                     } catch (Exception e1) {

                           System.out.println("Exception1:"+e1.getMessage());

                     }

                     // 4. configure the response object

              //     response.setContent(serializedResponse.getContent());

                     response.setStatusCode(HttpStatusCode.CREATED.getStatusCode());

                     response.setHeader(HttpHeader.CONTENT_TYPE,

                                  responseFormat.toContentTypeString());

                      }

              } else if (segmentCount == 2) {

                     throw new ODataApplicationException("Not implemented",

                                  HttpStatusCode.NOT_IMPLEMENTED.getStatusCode(), Locale.ROOT);

              } else {

                     // this would be the case for e.g.

                     // Students(1)/School/Students(1)/School

                     throw new ODataApplicationException("Not supported",

                                  HttpStatusCode.NOT_IMPLEMENTED.getStatusCode(), Locale.ROOT);

              }

       }