svn commit: r1606999 - /olingo/site/trunk/content/doc/tutorials/HandlingClobAndBlob.mdtext

[de...@apache.org]

Author: deepa
Date: Tue Jul  1 07:51:04 2014
New Revision: 1606999

URL: http://svn.apache.org/r1606999
Log:
CMS commit to olingo by deepa

Added:
    olingo/site/trunk/content/doc/tutorials/HandlingClobAndBlob.mdtext   (with props)

Added: olingo/site/trunk/content/doc/tutorials/HandlingClobAndBlob.mdtext
URL: http://svn.apache.org/viewvc/olingo/site/trunk/content/doc/tutorials/HandlingClobAndBlob.mdtext?rev=1606999&view=auto
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+Title:
+Notice:    Licensed to the Apache Software Foundation (ASF) under one
+           or more contributor license agreements.  See the NOTICE file
+           distributed with this work for additional information
+           regarding copyright ownership.  The ASF licenses this file
+           to you under the Apache License, Version 2.0 (the
+           "License"); you may not use this file except in compliance
+           with the License.  You may obtain a copy of the License at
+           .
+             http://www.apache.org/licenses/LICENSE-2.0
+           .
+           Unless required by applicable law or agreed to in writing,
+           software distributed under the License is distributed on an
+           "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+           KIND, either express or implied.  See the License for the
+           specific language governing permissions and limitations
+           under the License.
+
+## Handling BLOB and CLOB Data Types
+
+JPA entities can have properties that are of type java.sql.Blob or java.sql.Clob. Internally, JPA entities can instantiate a JPA provider (Eclipse Link or Hibernate or ...) specific implementation 
+
+of the above two interfaces and bind them to the properties. To enable write on such properties using OData JPA Processor Library, an additional access modifier is required to be added to the JPA 
+
+entities. Following is the proposal on how OData JPA Processor Library handles java.sql.Blob and java.sql.Clob during metadata generation and runtime processing. 
+
+### EDM Generation
+
+Based on the JPA entity property type, the pseudocode for generating the EDM is as below.
+
+For java.sql.Blob:
+
+1. Check if JPA entity property is of type byte[] or of type java.sql.Blob and annotated with @Lob annotation. 
+2. If Step 1 is true, then generate an EDM property with type as Edm.Binary
+
+For java.sql.Clob:
+
+1. Check if JPA entity property is of type java.sql.Clob and annotated with @Lob annotation. 
+2. If Step 1 is true, then generate an EDM property with type as Edm.String (with no max length unless a max length is specified). 
+
+### Runtime Processing
+
+**Prerequisite:**
+1. It is mandatory to implement the callback interface org.apache.olingo.odata2.jpa.processor.api.OnJPAWriteContent.
+2. The implemented interface needs to be registered with the service via the method 'setOnJPAWriteContent' part of 'ODataJPAServiceFactory'. 
+
+Following is the pseudocode for handling the java.sql.Blob and java.sql.Clob during runtime.
+
+		/* Callback Implementation */
+
+		public class OnDBWriteContent implements OnJPAWriteContent {
+
+		  @Override
+          public Blob getJPABlob(byte[] binaryData) throws ODataJPARuntimeException {
+            try {
+              return new JDBCBlob(binaryData);
+            } catch (SerialException e) {
+              ODataJPARuntimeException.throwException(ODataJPARuntimeException.INNER_EXCEPTION, e);
+            } catch (SQLException e) {
+              ODataJPARuntimeException.throwException(ODataJPARuntimeException.INNER_EXCEPTION, e);
+            }
+            return null;
+          }
+
+          @Override
+          public Clob getJPAClob(char[] characterData) throws ODataJPARuntimeException {
+            try {
+              return new JDBCClob(new String(characterData));
+            } catch (SQLException e) {
+              ODataJPARuntimeException.throwException(ODataJPARuntimeException.INNER_EXCEPTION, e);
+            }
+              return null;
+            }
+          }
+
+
+		/* Call Back registration in Service Factory */
+		public class JPAReferenceServiceFactory extends ODataJPAServiceFactory {
+
+		  public static final OnJPAWriteContent onDBWriteContent = new OnDBWriteContent();
+
+		  @Override
+          public ODataJPAContext initializeODataJPAContext()
+              throws ODataJPARuntimeException {
+
+			....
+			........
+			..............
+
+			setOnWriteJPAContent(onDBWriteContent); //Register Call Back
+
+			return oDataJPAContext;
+		   }
+		 }
+
+OData JPA Processor Library internally does the following:
+1. Checks if the JPA entity property is of type java.sql.Blob or java.sql.Clob.
+2. If Step 1 is true, then it invokes the registered callback method 'getJPABlob' or 'getJPAClob' respectively.
+3. If callback method is not defined, it throws an exception. 
+
+*Note*: Step 3 is needed because the OData JPA Processor Library is not bound to any specific implementation of Blob or Clob interface. 
+
+
+
+
+
+

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