[BAEL-1219] Code for Olingo V4 sample

apache-olingo/olingo4/pom.xml

@@ -52,7 +52,7 @@
 			<groupId>org.springframework.boot</groupId>
 			<artifactId>spring-boot-starter-web</artifactId>
 		</dependency>
-
+		
 		<dependency>
 			<groupId>org.apache.olingo</groupId>
 			<artifactId>odata-server-api</artifactId>

apache-olingo/olingo4/src/main/java/org/baeldung/examples/olingo4/ODataServiceConfiguration.java

@@ -14,33 +14,22 @@ import org.springframework.context.annotation.Configuration;
 
 @Configuration
 public class ODataServiceConfiguration {
-    
-    
-    @Bean
-    public ServletRegistrationBean<HttpServlet> odataServletRegistration(ODataHttpHandlerFactory factory, EntityManagerFactory emf) {
-        
-        ServletRegistrationBean bean = new ServletRegistrationBean(
-            odataServlet(factory,emf), 
-            "/odata/*");
-          bean.setLoadOnStartup(1);
-          return bean;
-    }
-    
 
     @Bean
-    public HttpServlet odataServlet(ODataHttpHandlerFactory factory, EntityManagerFactory emf ) {
+    public ServletRegistrationBean<HttpServlet> odataServletRegistration(ODataHttpHandlerFactory factory) {
-        
+        ServletRegistrationBean<HttpServlet> srb = 
-        return new ODataServlet(factory,emf);
+          new ServletRegistrationBean<>(new ODataServlet(factory), "/odata/*");
+        srb.setLoadOnStartup(1);
+        return srb;
     }
-    
+
-    
     @Bean
     public ODataHttpHandlerFactory httpHandlerFactory(CsdlEdmProvider edmProvider, ODataFactory odataFactory, List<Processor> processors) {
         return new ODataHttpHandlerFactoryImplBuilder()
-            .edmProvider(edmProvider)
+          .edmProvider(edmProvider)
-            .odataFactory(odataFactory)
+          .odataFactory(odataFactory)
-            .processors(processors)
+          .processors(processors)
-            .build();
+          .build();
     }
 
 }

apache-olingo/olingo4/src/main/java/org/baeldung/examples/olingo4/ODataServlet.java

@@ -25,7 +25,7 @@ public class ODataServlet extends HttpServlet {
     private final ODataHttpHandlerFactory odataHttpHandlerFactory;
     
     
-    public ODataServlet(ODataHttpHandlerFactory factory, EntityManagerFactory emf) {
+    public ODataServlet(ODataHttpHandlerFactory factory) {
         this.odataHttpHandlerFactory = factory;
     }
 

apache-olingo/olingo4/src/main/java/org/baeldung/examples/olingo4/edm/JpaEdmProvider.java

@@ -62,8 +62,9 @@ public class JpaEdmProvider extends CsdlAbstractEdmProvider {
 
             if (e != null) {
                 CsdlEntitySet entitySet = new CsdlEntitySet();
-                entitySet.setName(entitySetName);
+                entitySet
-                entitySet.setType(new FullQualifiedName(NAMESPACE, e.getName()));
+                  .setName(entitySetName)
+                  .setType(new FullQualifiedName(NAMESPACE, e.getName()));
                 return entitySet;
             }
         }
@@ -135,7 +136,6 @@ public class JpaEdmProvider extends CsdlAbstractEdmProvider {
             .map((e) -> {
                 try {
                     // Here we use a simple mapping strategy to map entity types to entity set names:
-                    // 
                     return getEntitySet(CONTAINER, e.getName() + "s");
                 } catch (ODataException oe) {
                     throw new RuntimeException(oe);
@@ -197,12 +197,22 @@ public class JpaEdmProvider extends CsdlAbstractEdmProvider {
 
         result.setKey(ids);
 
-        // Process navs
+        // Process 1:N navs
         List<CsdlNavigationProperty> navs = et.getDeclaredPluralAttributes()
             .stream()
             .map(attr -> buildNavAttribute(et, attr))
             .collect(Collectors.toList());
         result.setNavigationProperties(navs);
+        
+        // Process N:1 navs
+        List<CsdlNavigationProperty> navs2 = et.getDeclaredSingularAttributes()
+            .stream()
+            .filter(attr -> attr.getPersistentAttributeType() == PersistentAttributeType.MANY_TO_ONE)
+            .map(attr -> buildNavAttribute(et, attr))
+            .collect(Collectors.toList());
+
+        result.getNavigationProperties().addAll(navs2);
+        
 
         return result;
     }
@@ -225,13 +235,26 @@ public class JpaEdmProvider extends CsdlAbstractEdmProvider {
         return p;
     }
 
+    // Build NavProperty for 1:N or M:N associations
     private CsdlNavigationProperty buildNavAttribute(EntityType<?> et, PluralAttribute<?, ?, ?> attr) {
 
         CsdlNavigationProperty p = new CsdlNavigationProperty().setName(attr.getName())
             .setType(new FullQualifiedName(NAMESPACE, attr.getBindableJavaType().getSimpleName()))
-            .setNullable(false); // for now
+            .setCollection(true)
+            .setNullable(false); 
 
         return p;
     }
 
+    // Build NavProperty for N:1 associations
+    private CsdlNavigationProperty buildNavAttribute(EntityType<?> et, SingularAttribute<?, ?> attr) {
+
+        CsdlNavigationProperty p = new CsdlNavigationProperty().setName(attr.getName())
+            .setType(new FullQualifiedName(NAMESPACE, attr.getBindableJavaType().getSimpleName()))
+            .setCollection(false)
+            .setNullable(attr.isOptional());
+
+        return p;
+    }
+    
 }

apache-olingo/olingo4/src/main/java/org/baeldung/examples/olingo4/processor/JpaEntityCollectionProcessor.java

@@ -48,10 +48,12 @@ public class JpaEntityCollectionProcessor implements CountEntityCollectionProces
     private ServiceMetadata serviceMetadata;
     private EntityManagerFactory emf;
     private RepositoryRegistry repositoryRegistry;
+    private JpaEntityMapper entityMapper;
 
-    public JpaEntityCollectionProcessor(EntityManagerFactory emf, RepositoryRegistry repositoryRegistry) {
+    public JpaEntityCollectionProcessor(EntityManagerFactory emf, RepositoryRegistry repositoryRegistry, JpaEntityMapper entityMapper) {
         this.emf = emf;
         this.repositoryRegistry = repositoryRegistry;
+        this.entityMapper = entityMapper;
     }
 
     @Override
@@ -115,71 +117,40 @@ public class JpaEntityCollectionProcessor implements CountEntityCollectionProces
 
     }
 
-    private EntityCollection getData(EdmEntitySet edmEntitySet, UriInfo uriInfo) {
+    /**
+     * Helper method to retrieve all entities of an entity set from an the backend database
+     * @param edmEntitySet
+     * @param uriInfo
+     * @return
+     */
+    protected EntityCollection getData(EdmEntitySet edmEntitySet, UriInfo uriInfo) {
 
         EdmEntityType type = edmEntitySet.getEntityType();
-        JpaRepository<?, ?> repo = repositoryRegistry.getRepositoryForEntity(type);
+        JpaRepository<?, ?> repo = (JpaRepository<?, ?>)repositoryRegistry.getRepositoryForEntity(type);
         EntityCollection result = new EntityCollection();
 
         repo.findAll()
             .stream()
             .forEach((it) -> result.getEntities()
-                .add(map2entity(edmEntitySet, it)));
+                .add(entityMapper.map2entity(edmEntitySet, it)));
 
         return result;
     }
 
-    private Entity map2entity(EdmEntitySet edmEntitySet, Object entry) {
-
-        EntityType<?> et = emf.getMetamodel()
-            .entity(entry.getClass());
-
-
-        Entity e = new Entity();
-        try {
-            // First, we set the entity's primary key
-            
-            // Now map all properties
-            et.getDeclaredSingularAttributes().stream()
-              .forEach( (attr) -> {
-                 if ( !attr.isAssociation()) {
-                     Object v = getPropertyValue(entry,attr.getName());
-                     Property p = new Property(null, attr.getName(),ValueType.PRIMITIVE,v);
-                     e.addProperty(p);
-
-                     if ( attr.isId()) {
-                         e.setId(createId(edmEntitySet.getName(),v));                     
-                     }                     
-                 }
-                 
-              });
-            
-        } catch (Exception ex) {
-            throw new ODataRuntimeException("[E141] Unable to create OData entity", ex);
-        }
-
-        return e;
-    }
-    
-    private Object getPropertyValue(Object entry, String name) {
-        try {
-            return PropertyUtils.getProperty(entry,name);
-        } catch (IllegalAccessException | InvocationTargetException | NoSuchMethodException e) {
-            throw new ODataRuntimeException("[E141] Unable to read property from entity, property=" + name, e);
-        }
-    }
-
-    private URI createId(String entitySetName, Object id)  {
-        try {
-            return new URI(entitySetName + "(" + String.valueOf(id) + ")");
-        } catch (URISyntaxException e) {
-            throw new ODataRuntimeException("[E177] Unable to create URI", e);
-        }
-    }
 
+    /**
+     * Helper method to get the total size of an entity set
+     * @param edmEntitySet
+     * @param uriInfo
+     * @return
+     */
     private Long getCount(EdmEntitySet edmEntitySet, UriInfo uriInfo) {
-        // TODO Auto-generated method stub
+        
-        return null;
+        EdmEntityType type = edmEntitySet.getEntityType();
+        JpaRepository<?, ?> repo = (JpaRepository<?, ?>)repositoryRegistry.getRepositoryForEntity(type);
+        EntityCollection result = new EntityCollection();
+
+        return repo.count();
     }
 
 }

apache-olingo/olingo4/src/main/java/org/baeldung/examples/olingo4/processor/JpaEntityMapper.java

@@ -0,0 +1,84 @@
+/**
+ * 
+ */
+package org.baeldung.examples.olingo4.processor;
+
+import java.lang.reflect.InvocationTargetException;
+import java.net.URI;
+import java.net.URISyntaxException;
+
+import javax.persistence.EntityManagerFactory;
+import javax.persistence.metamodel.EntityType;
+
+import org.apache.commons.beanutils.PropertyUtils;
+import org.apache.olingo.commons.api.data.Entity;
+import org.apache.olingo.commons.api.data.Property;
+import org.apache.olingo.commons.api.data.ValueType;
+import org.apache.olingo.commons.api.edm.EdmEntitySet;
+import org.apache.olingo.commons.api.ex.ODataRuntimeException;
+import org.springframework.stereotype.Component;
+
+/**
+ * <p>Helper class that converts a JPA entity into an OData entity using
+ * available metadata from the JPA's EntityManagerFactory.</p>
+ * 
+ * @author Philippe
+ *
+ */
+@Component
+public class JpaEntityMapper {
+    
+    private EntityManagerFactory emf;
+
+    public JpaEntityMapper(EntityManagerFactory emf) {
+        this.emf = emf;
+    }
+    
+    
+    public Entity map2entity(EdmEntitySet edmEntitySet, Object entry) {
+
+        EntityType<?> et = emf.getMetamodel()
+            .entity(entry.getClass());
+
+
+        Entity e = new Entity();
+        try {
+            et.getDeclaredSingularAttributes().stream()
+              .forEach( (attr) -> {
+                 if ( !attr.isAssociation()) {
+                     Object v = getPropertyValue(entry,attr.getName());
+                     Property p = new Property(null, attr.getName(),ValueType.PRIMITIVE,v);
+                     e.addProperty(p);
+
+                     if ( attr.isId()) {
+                         e.setId(createId(edmEntitySet.getName(),v));                     
+                     }                     
+                 }                 
+              });
+        } catch (Exception ex) {
+            throw new ODataRuntimeException("[E141] Unable to create OData entity", ex);
+        }
+
+        return e;
+    }
+    
+    
+    private Object getPropertyValue(Object entry, String name) {
+        try {
+            return PropertyUtils.getProperty(entry,name);
+        } catch (IllegalAccessException | InvocationTargetException | NoSuchMethodException e) {
+            throw new ODataRuntimeException("[E141] Unable to read property from entity, property=" + name, e);
+        }
+    }
+
+    private URI createId(String entitySetName, Object id)  {
+        try {
+            return new URI(entitySetName + "(" + String.valueOf(id) + ")");
+        } catch (URISyntaxException e) {
+            throw new ODataRuntimeException("[E177] Unable to create URI", e);
+        }
+    }
+    
+
+
+}

apache-olingo/olingo4/src/main/java/org/baeldung/examples/olingo4/processor/JpaEntityProcessor.java

@@ -0,0 +1,378 @@
+/**
+ * 
+ */
+package org.baeldung.examples.olingo4.processor;
+
+import java.io.InputStream;
+import java.lang.reflect.Member;
+import java.util.Collection;
+import java.util.List;
+import java.util.Locale;
+import java.util.stream.Collectors;
+
+import javax.persistence.EntityManagerFactory;
+import javax.persistence.criteria.CriteriaBuilder;
+import javax.persistence.criteria.CriteriaQuery;
+import javax.persistence.criteria.Predicate;
+import javax.persistence.criteria.Root;
+import javax.persistence.metamodel.SingularAttribute;
+
+import org.apache.commons.beanutils.PropertyUtils;
+import org.apache.olingo.commons.api.data.ContextURL;
+import org.apache.olingo.commons.api.data.Entity;
+import org.apache.olingo.commons.api.data.EntityCollection;
+import org.apache.olingo.commons.api.edm.EdmEntitySet;
+import org.apache.olingo.commons.api.edm.EdmEntityType;
+import org.apache.olingo.commons.api.edm.EdmNavigationProperty;
+import org.apache.olingo.commons.api.edm.EdmType;
+import org.apache.olingo.commons.api.ex.ODataRuntimeException;
+import org.apache.olingo.commons.api.format.ContentType;
+import org.apache.olingo.commons.api.http.HttpHeader;
+import org.apache.olingo.commons.api.http.HttpStatusCode;
+import org.apache.olingo.server.api.OData;
+import org.apache.olingo.server.api.ODataApplicationException;
+import org.apache.olingo.server.api.ODataLibraryException;
+import org.apache.olingo.server.api.ODataRequest;
+import org.apache.olingo.server.api.ODataResponse;
+import org.apache.olingo.server.api.ServiceMetadata;
+import org.apache.olingo.server.api.processor.EntityProcessor;
+import org.apache.olingo.server.api.serializer.EntityCollectionSerializerOptions;
+import org.apache.olingo.server.api.serializer.EntitySerializerOptions;
+import org.apache.olingo.server.api.serializer.ODataSerializer;
+import org.apache.olingo.server.api.serializer.SerializerException;
+import org.apache.olingo.server.api.serializer.SerializerResult;
+import org.apache.olingo.server.api.uri.UriInfo;
+import org.apache.olingo.server.api.uri.UriParameter;
+import org.apache.olingo.server.api.uri.UriResource;
+import org.apache.olingo.server.api.uri.UriResourceEntitySet;
+import org.apache.olingo.server.api.uri.UriResourceNavigation;
+import org.baeldung.examples.olingo4.repository.EdmEntityRepository;
+import org.baeldung.examples.olingo4.repository.RepositoryRegistry;
+import org.springframework.data.jpa.domain.Specification;
+import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.data.jpa.repository.JpaSpecificationExecutor;
+import org.springframework.stereotype.Component;
+
+/**
+ * JpaEntityProcessor adapter. 
+ * <p>This implementation is heavily based on the Tutorial available
+ * at Olingo's site. It is meant to be an starting point for an actual implementation.</p>
+ * <p>Please note that many features from a full-fledged are missing
+ * @author Philippe
+ *
+ */
+@Component
+public class JpaEntityProcessor implements EntityProcessor {
+    
+    private EntityManagerFactory emf;
+    private OData odata;
+    private ServiceMetadata serviceMetadata;
+    private RepositoryRegistry registry;
+    private JpaEntityMapper entityMapper;
+
+    public JpaEntityProcessor(EntityManagerFactory emf, RepositoryRegistry registry, JpaEntityMapper entityMapper) {
+        this.emf = emf;
+        this.registry = registry;
+        this.entityMapper = entityMapper;
+    }
+
+    /* (non-Javadoc)
+     * @see org.apache.olingo.server.api.processor.Processor#init(org.apache.olingo.server.api.OData, org.apache.olingo.server.api.ServiceMetadata)
+     */
+    @Override
+    public void init(OData odata, ServiceMetadata serviceMetadata) {
+        this.odata = odata;
+        this.serviceMetadata = serviceMetadata;
+        
+    }
+
+    /* (non-Javadoc)
+     * @see org.apache.olingo.server.api.processor.EntityProcessor#readEntity(org.apache.olingo.server.api.ODataRequest, org.apache.olingo.server.api.ODataResponse, org.apache.olingo.server.api.uri.UriInfo, org.apache.olingo.commons.api.format.ContentType)
+     */
+    @Override
+    public void readEntity(ODataRequest request, ODataResponse response, UriInfo uriInfo, ContentType responseFormat) throws ODataApplicationException, ODataLibraryException {
+
+        // First, we have to figure out which entity is requested
+        List<UriResource> resourceParts = uriInfo.getUriResourceParts();
+        InputStream entityStream;
+        
+        UriResourceEntitySet rootResourceEntitySet = (UriResourceEntitySet) resourceParts.get(0);
+        EdmEntitySet rootEntitySet = rootResourceEntitySet.getEntitySet();        
+        List<UriParameter> rootPredicates = rootResourceEntitySet.getKeyPredicates();
+        EdmEntityType rootEntityType = rootEntitySet.getEntityType();
+
+        
+        if ( resourceParts.size() == 1 ) {
+            entityStream = readEntity(rootEntitySet,rootPredicates,responseFormat);
+        }
+        else if ( resourceParts.size() == 2 ) {
+            UriResource part = resourceParts.get(1);
+            if ( !(part instanceof UriResourceNavigation)) {
+                throw new ODataRuntimeException("[E103] part type not supported: class=" + part.getClass().getName());
+            }
+
+            UriResourceNavigation navSegment = (UriResourceNavigation)part;
+            
+            // We have three scenarios we must handle:
+            // Entity(x)/Related, where Related is a 1:N or M:N relationship => result is a collection
+            // Entity(x)/Related, where Related is a N:1 or 1:1 relationship => result is a single entity
+            // Entity(x)/Related(z), where Related is a 1:N or M:N relationship => result is a single entity
+            if (navSegment.getKeyPredicates().isEmpty()) {
+                if ( isOne2ManyProperty(rootEntityType,navSegment.getProperty())) {
+                    entityStream = readRelatedEntities(rootEntitySet,rootPredicates,navSegment.getProperty(),responseFormat);
+                }
+                else {
+                    // The relation must point to another entity type, so casting should be safe here
+                    EdmEntityType resultType = (EdmEntityType)rootEntityType.getNavigationProperty(navSegment.getProperty().getName()).getType();
+                    EdmEntitySet resultEntitySet = entitySetFromType(resultType);
+                    
+                    entityStream = readEntity(resultEntitySet, navSegment.getKeyPredicates(), responseFormat);
+                }
+            }
+            else {
+                entityStream = readRelatedEntity(request, rootEntitySet,rootPredicates,navSegment.getProperty(),navSegment.getKeyPredicates(),responseFormat);
+            }
+            
+        }
+        else {
+            // For now, we'll only allow navigation just to directly linked navs
+            throw new ODataApplicationException("[E109] Multi-level navigation not supported", HttpStatusCode.NOT_IMPLEMENTED.getStatusCode(), Locale.ROOT);
+        }
+
+        //4. configure the response object
+        response.setContent(entityStream);
+        response.setStatusCode(HttpStatusCode.OK.getStatusCode());
+        response.setHeader(HttpHeader.CONTENT_TYPE, responseFormat.toContentTypeString());       
+        
+    }
+    
+
+    // Lookup the EntitySet associated with an EntityType
+    // In our example, we assume we have only one entityset for each entity type
+    private EdmEntitySet entitySetFromType(EdmEntityType type) {
+        return serviceMetadata
+          .getEdm()
+          .getEntityContainer()
+          .getEntitySets()
+          .stream()
+          .filter((s) -> s.getEntityType().getName().equals(type.getName()))
+          .findFirst()
+          .orElseThrow(() -> new ODataRuntimeException("[E144] No entity set found for type " + type.getFullQualifiedName()));
+    }
+
+    // 
+    private boolean isOne2ManyProperty(EdmEntityType entityType, EdmNavigationProperty property) {        
+        return entityType.getProperty(property.getName()) != null && property.isCollection();
+    }
+
+    private InputStream readEntity(EdmEntitySet entitySet, List<UriParameter> keyPredicates,ContentType responseFormat) throws ODataApplicationException, ODataLibraryException {
+        
+        Entity entity = readEntityData(entitySet,keyPredicates);
+        
+        ContextURL contextUrl = ContextURL.with().entitySet(entitySet).build();
+        // expand and select currently not supported
+        EntitySerializerOptions options = EntitySerializerOptions
+          .with()
+          .contextURL(contextUrl)
+          .build();
+
+        ODataSerializer serializer = odata.createSerializer(responseFormat);
+        
+        SerializerResult serializerResult = serializer.entity(serviceMetadata, entitySet.getEntityType(), entity, options);
+        return serializerResult.getContent();
+    }
+    
+    private InputStream readRelatedEntities(EdmEntitySet rootEntitySet, List<UriParameter> rootPredicates, EdmNavigationProperty property, ContentType responseFormat) throws ODataApplicationException {
+
+        Object jpaEntity = readJPAEntity(rootEntitySet, rootPredicates);
+        try {
+            Object set = PropertyUtils.getProperty(jpaEntity, property.getName());
+            EdmEntitySet entitySet = entitySetFromType(property.getType());
+            ContextURL contextUrl = ContextURL
+              .with()
+              .entitySet(entitySet)
+              .build();
+            
+            EntityCollectionSerializerOptions options = EntityCollectionSerializerOptions
+              .with()
+              .contextURL(contextUrl)
+              .build();
+            
+            EntityCollection result = new EntityCollection();
+            
+            ((Collection<Object>)set)
+              .stream()
+              .map((o) -> this.entityMapper.map2entity(entitySet, o))
+              .forEach((e) -> result.getEntities().add(e));
+
+            ODataSerializer serializer = odata.createSerializer(responseFormat);            
+            SerializerResult serializerResult = serializer.entityCollection(serviceMetadata, property.getType(), result, options);
+            return serializerResult.getContent();
+        }
+        catch(Exception ex) {
+            throw new ODataRuntimeException("[E181] Error accessing database", ex);
+        }
+    }
+    
+    @SuppressWarnings({ "rawtypes", "serial", "unchecked" })
+    private InputStream readRelatedEntity(ODataRequest request, EdmEntitySet rootEntitySet, List<UriParameter> rootPredicates, EdmNavigationProperty property, List<UriParameter> predicates, ContentType responseFormat) throws ODataApplicationException, SerializerException {
+
+
+        JpaSpecificationExecutor<Object> rootRepo =  (JpaSpecificationExecutor<Object>)registry.getRepositoryForEntity(rootEntitySet.getEntityType());
+        JpaSpecificationExecutor<Object> repo =  (JpaSpecificationExecutor<Object>)registry.getRepositoryForEntity(property.getType());
+
+        // We assume here that we have a bi-directional 1:N relationship, so we'll
+        // always have a property in the child entity that points to the parent
+        Class<?> rootClass = ((EdmEntityRepository)rootRepo).getEntityClass();
+        Class<?> childClass = ((EdmEntityRepository)repo).getEntityClass();
+        SingularAttribute fk = emf.getMetamodel()
+          .entity(childClass)
+          .getSingularAttributes()
+          .stream()
+          .filter((attr) -> attr.isAssociation() && attr.getJavaType().isAssignableFrom(rootClass))
+          .findFirst()
+          .orElse(null);
+        
+        SingularAttribute pk = emf.getMetamodel()
+            .entity(childClass)
+            .getId(Long.class);
+        
+        SingularAttribute rootPk = emf.getMetamodel()
+            .entity(rootClass)
+            .getId(Long.class);
+        
+        if ( fk == null ) {
+            throw new ODataRuntimeException("[E230] No singular attribute of child class '" + childClass.getName() + "' found" );
+        }
+        
+        
+        Specification spec = new Specification() {
+            @Override
+            public Predicate toPredicate(Root root, CriteriaQuery q, CriteriaBuilder cb) {
+                
+                try {
+                    Object rootInstance = rootClass.newInstance();
+                    PropertyUtils.setProperty(rootInstance, rootPk.getName(), getEntityKey(rootEntitySet.getEntityType(),rootPredicates));
+                    
+                    final Predicate p = cb.and(
+                        cb.equal(
+                          root.get(pk),
+                          getEntityKey(property.getType(),predicates)),
+                        cb.equal(
+                          root.get(fk),
+                          rootInstance));
+                    
+                    return p;
+                }
+                catch(Exception ex) {
+                    throw new ODataRuntimeException(ex);
+                }
+                
+            }
+         };
+            
+        // Read data from DB 
+        EdmEntitySet relatedEntitySet = entitySetFromType(property.getType());
+        EntityCollection data = new EntityCollection();
+        
+        repo.findAll(spec)
+           .stream()
+           .forEach((entry) -> data.getEntities().add(entityMapper.map2entity(relatedEntitySet, entry)));
+
+        // 
+        
+        ODataSerializer serializer = odata.createSerializer(responseFormat);
+
+        // 4th: Now serialize the content: transform from the EntitySet object to InputStream
+        EdmEntityType edmEntityType = relatedEntitySet.getEntityType();
+        ContextURL contextUrl = ContextURL.with()
+            .entitySet(relatedEntitySet)
+            .build();
+
+        final String id = request.getRawBaseUri() + "/" + relatedEntitySet.getName();
+        EntityCollectionSerializerOptions opts = EntityCollectionSerializerOptions.with()
+            .id(id)
+            .contextURL(contextUrl)
+            .build();
+        SerializerResult serializerResult = serializer.entityCollection(serviceMetadata, edmEntityType, data, opts);
+        InputStream serializedContent = serializerResult.getContent();
+
+        
+        return serializedContent;
+    }
+    
+
+    /**
+     * This method returns a speficic entity given its primary key
+     * @param edmEntitySet
+     * @param keyPredicates
+     * @return
+     */
+    protected Entity readEntityData(EdmEntitySet edmEntitySet, List<UriParameter> keyPredicates) throws ODataApplicationException {
+        
+        Object jpaEntry = readJPAEntity(edmEntitySet, keyPredicates); 
+        Entity e = entityMapper.map2entity(edmEntitySet, jpaEntry);        
+        return e;
+    }
+    
+    private Object readJPAEntity(EdmEntitySet edmEntitySet, List<UriParameter> keyPredicates) throws ODataApplicationException {
+        EdmEntityType type = edmEntitySet.getEntityType();        
+        JpaRepository<Object,Object> repo =  (JpaRepository<Object,Object>)registry.getRepositoryForEntity(type);
+        
+        // Get key value
+        Object keyValue =  getEntityKey(type,keyPredicates);
+        Object entry = repo
+          .findById(keyValue)
+          .orElseThrow(
+             () -> new ODataApplicationException("[E116] NO entity found for the given key",
+                                       HttpStatusCode.NOT_FOUND.getStatusCode(), Locale.ENGLISH));
+       
+        return entry;
+    }
+
+    private Object getEntityKey(EdmEntityType type, List<UriParameter> keyPredicates) {
+        
+        if ( keyPredicates.size() > 1 ) {
+            throw new ODataRuntimeException("[E131] Composite keys are not supported");
+        }
+        
+        // For now, we'll assume we only have numeric keys.
+        UriParameter keyParam = keyPredicates.get(0);
+        try {
+            return Long.parseLong(keyParam.getText());
+        }
+        catch(NumberFormatException nfe) {
+            throw new ODataRuntimeException("[E140] Invalid key value. Only numeric keys are supported by this service");
+        }
+        
+        
+    }
+
+    /* (non-Javadoc)
+     * @see org.apache.olingo.server.api.processor.EntityProcessor#createEntity(org.apache.olingo.server.api.ODataRequest, org.apache.olingo.server.api.ODataResponse, org.apache.olingo.server.api.uri.UriInfo, org.apache.olingo.commons.api.format.ContentType, org.apache.olingo.commons.api.format.ContentType)
+     */
+    @Override
+    public void createEntity(ODataRequest request, ODataResponse response, UriInfo uriInfo, ContentType requestFormat, ContentType responseFormat) throws ODataApplicationException, ODataLibraryException {
+        // TODO Auto-generated method stub
+
+    }
+
+    /* (non-Javadoc)
+     * @see org.apache.olingo.server.api.processor.EntityProcessor#updateEntity(org.apache.olingo.server.api.ODataRequest, org.apache.olingo.server.api.ODataResponse, org.apache.olingo.server.api.uri.UriInfo, org.apache.olingo.commons.api.format.ContentType, org.apache.olingo.commons.api.format.ContentType)
+     */
+    @Override
+    public void updateEntity(ODataRequest request, ODataResponse response, UriInfo uriInfo, ContentType requestFormat, ContentType responseFormat) throws ODataApplicationException, ODataLibraryException {
+        // TODO Auto-generated method stub
+
+    }
+
+    /* (non-Javadoc)
+     * @see org.apache.olingo.server.api.processor.EntityProcessor#deleteEntity(org.apache.olingo.server.api.ODataRequest, org.apache.olingo.server.api.ODataResponse, org.apache.olingo.server.api.uri.UriInfo)
+     */
+    @Override
+    public void deleteEntity(ODataRequest request, ODataResponse response, UriInfo uriInfo) throws ODataApplicationException, ODataLibraryException {
+        // TODO Auto-generated method stub
+
+    }
+
+}

apache-olingo/olingo4/src/main/java/org/baeldung/examples/olingo4/repository/CarMakerRepository.java

@@ -6,7 +6,11 @@ import org.springframework.data.jpa.repository.JpaSpecificationExecutor;
 import org.springframework.stereotype.Repository;
 
 @Repository
-public interface CarMakerRepository extends JpaRepository<CarMaker, Long>, JpaSpecificationExecutor<CarMaker>, EdmEntityRepository {
+public interface CarMakerRepository extends EdmEntityRepository<CarMaker>, JpaRepository<CarMaker, Long>, JpaSpecificationExecutor<CarMaker> {
 
     public default String getEdmEntityName() { return CarMaker.class.getSimpleName();}
+    @Override
+    default Class<CarMaker> getEntityClass() {
+        return CarMaker.class;
+    }
 }

apache-olingo/olingo4/src/main/java/org/baeldung/examples/olingo4/repository/CarModelRepository.java

@@ -1,13 +1,22 @@
 package org.baeldung.examples.olingo4.repository;
 
+import java.util.List;
+
 import org.baeldung.examples.olingo4.domain.CarModel;
 import org.springframework.data.jpa.repository.JpaRepository;
 import org.springframework.data.jpa.repository.JpaSpecificationExecutor;
 import org.springframework.stereotype.Repository;
 
 @Repository
-public interface CarModelRepository extends JpaRepository<CarModel, Long>, JpaSpecificationExecutor<CarModel>,EdmEntityRepository {
+public interface CarModelRepository extends EdmEntityRepository<CarModel>, JpaRepository<CarModel, Long>, JpaSpecificationExecutor<CarModel> {
 
+    public List<CarModel> findByMakerId(Long makerId);
+    
     public default String getEdmEntityName() { return CarModel.class.getSimpleName();}
+    
+    @Override
+    default Class<CarModel> getEntityClass() {
+        return CarModel.class;
+    }
 
 }

apache-olingo/olingo4/src/main/java/org/baeldung/examples/olingo4/repository/EdmEntityRepository.java

@@ -8,8 +8,10 @@ package org.baeldung.examples.olingo4.repository;
  * @author Philippe
  *
  */
-public interface EdmEntityRepository {
+public interface EdmEntityRepository<E>  {
     
     public String getEdmEntityName();
+    public Class<E> getEntityClass();
+
 
 }

apache-olingo/olingo4/src/main/java/org/baeldung/examples/olingo4/repository/RepositoryRegistry.java

@@ -5,24 +5,23 @@ import java.util.List;
 import java.util.Map;
 
 import org.apache.olingo.commons.api.edm.EdmEntityType;
-import org.springframework.data.jpa.repository.JpaRepository;
 import org.springframework.stereotype.Component;
 
 @Component
 public class RepositoryRegistry {
     
-    private Map<String,JpaRepository<?,?>> repositoriesByClassName = new HashMap<>();
+    private Map<String,EdmEntityRepository<?>> repositoriesByClassName = new HashMap<>();
 
-    public RepositoryRegistry(List<EdmEntityRepository> allRepositories) {
+    public RepositoryRegistry(List<EdmEntityRepository<?>> allRepositories) {
         
         allRepositories.stream().forEach((r) ->  
-        repositoriesByClassName.put(r.getEdmEntityName(),(JpaRepository<?,?>)r));
+        repositoriesByClassName.put(r.getEdmEntityName(),(EdmEntityRepository<?>)r));
         
     }
     
     
-    public JpaRepository<?, ?> getRepositoryForEntity(EdmEntityType entityType) {        
+    public EdmEntityRepository<?> getRepositoryForEntity(EdmEntityType entityType) {        
-        JpaRepository<?, ?> repo = repositoriesByClassName.get(entityType.getName());
+        EdmEntityRepository<?> repo = repositoriesByClassName.get(entityType.getName());
         return repo;
     }
 }

apache-olingo/olingo4/src/main/resources/application.properties

@@ -1,3 +1,6 @@
+server:
+	port: 8080
+	
 spring:    
   jpa:
     show-sql: true