[Mulgara-svn] r927 - trunk/src/jar/resolver/java/org/mulgara/resolver

[pag at mulgara.org]

Author: pag
Date: 2008-05-13 20:51:33 -0700 (Tue, 13 May 2008)
New Revision: 927

Added:
   trunk/src/jar/resolver/java/org/mulgara/resolver/CreateDefaultGraphOperation.java
Log:
New operation to create a Default Graph for a resolver. This is a different mechanism to standard graph creation, as it is a bootstrap operation.

Added: trunk/src/jar/resolver/java/org/mulgara/resolver/CreateDefaultGraphOperation.java
===================================================================
--- trunk/src/jar/resolver/java/org/mulgara/resolver/CreateDefaultGraphOperation.java	                        (rev 0)
+++ trunk/src/jar/resolver/java/org/mulgara/resolver/CreateDefaultGraphOperation.java	2008-05-14 03:51:33 UTC (rev 927)
@@ -0,0 +1,129 @@
+/*
+ * The contents of this file are subject to the Open Software License
+ * Version 3.0 (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.opensource.org/licenses/osl-3.0.txt
+ *
+ * Software distributed under the License is distributed on an "AS IS"
+ * basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
+ * the License for the specific language governing rights and limitations
+ * under the License.
+ */
+
+package org.mulgara.resolver;
+
+// Java 2 standard packages
+import java.net.URI;
+
+// Third party packages
+import org.apache.log4j.Logger;
+import org.jrdf.graph.*;
+
+// Local packages
+import org.mulgara.query.*;
+import org.mulgara.query.rdf.*;
+import org.mulgara.resolver.spi.*;
+import org.mulgara.server.Session;
+import org.mulgara.store.nodepool.NodePool;
+
+/**
+ * An {@link Operation} that implements the {@link Session#createDefaultGraph} method.
+ *
+ * @created May 8, 2008
+ * @author Paul Gearon
+ * @copyright &copy; 2008 <a href="http://www.topazproject.org/">The Topaz Project</a>
+ * @licence <a href="{@docRoot}/../../LICENCE.txt">Open Software License v3.0</a>
+ */
+class CreateDefaultGraphOperation implements Operation {
+  /** Logger. This is named after the class. */
+  @SuppressWarnings("unused")
+  private static final Logger logger = Logger.getLogger(CreateDefaultGraphOperation.class.getName());
+
+  /** The URI of the model to be created. */
+  private final URI graphURI;
+
+  /** The URI of the type of the model to be created. */
+  private URI graphTypeURI;
+
+  /** A flag to indicate that a graph was created by this operation. */
+  private boolean created = false;
+
+  /**
+   * Sole constructor.
+   * @param graphURI  the {@link URI} of the graph to be created, never <code>null</code>
+   * @param graphTypeURI  thie {@link URI} of the type of graph to create, or
+   *       <code>null</code> for the same type as the system graph (<code>#</code>)
+   * @throws IllegalArgumentException if <var>graphURI</var> or <var>graphTypeURI</var> is <code>null</code>
+   */
+  CreateDefaultGraphOperation(URI graphURI, URI graphTypeURI) throws QueryException {
+    // Validate parameters
+    if (graphURI == null) throw new IllegalArgumentException("Null \"graphURI\" parameter");
+    if (graphTypeURI == null) throw new IllegalArgumentException("Null \"graphTypeURI\" parameter");
+    // Initialize fields
+    this.graphURI     = graphURI;
+    this.graphTypeURI = graphTypeURI;
+  }
+
+  /**
+   * @see org.mulgara.resolver.Operation#execute(org.mulgara.resolver.OperationContext, org.mulgara.resolver.spi.SystemResolver, org.mulgara.resolver.spi.DatabaseMetadata)
+   */
+  public void execute(OperationContext operationContext, SystemResolver systemResolver,
+                      DatabaseMetadata metadata) throws Exception {
+    // Find the local node identifying the model
+    long graph = systemResolver.localizePersistent(new URIReferenceImpl(graphURI));
+    long graphType = systemResolver.localizePersistent(new URIReferenceImpl(graphTypeURI));
+    assert graph != NodePool.NONE;
+    assert graphType != NodePool.NONE;
+
+    // Check graph does not already exist with a different model type.
+    Resolution resolution = systemResolver.resolve(new ConstraintImpl(
+        new LocalNode(graph),
+        new LocalNode(metadata.getRdfTypeNode()),
+        new Variable("x"),
+        new LocalNode(metadata.getSystemModelNode())));
+
+    try {
+      resolution.beforeFirst();
+      if (resolution.next()) {
+        Node eNode = systemResolver.globalize(resolution.getColumnValue(0));
+        try {
+          URIReferenceImpl existing = (URIReferenceImpl)eNode;
+          if (!existing.equals(new URIReferenceImpl(graphTypeURI))) {
+            throw new QueryException(graphURI + " already exists with model type " + existing +
+                " in attempt to create it with type " + graphTypeURI);
+          }
+          // graph exists and is correct. created stays false
+          return;
+        } catch (ClassCastException ec) {
+          throw new QueryException("Invalid model type entry in system model: " + graphURI + " <rdf:type> " + eNode);
+        }
+      }
+    } finally {
+      resolution.close();
+    }
+
+    // Find the local node identifying the system graph and rdf:type
+    long sysGraph = metadata.getSystemModelNode();
+    long rdfType = metadata.getRdfTypeNode();
+
+    // Use the session to create the model
+    systemResolver.modifyModel(sysGraph, new SingletonStatements(graph, rdfType, graphType), true);
+
+    created = true;
+  }
+
+  /**
+   * @return <code>true</code>
+   */
+  public boolean isWriteOperation() {
+    return true;
+  }
+
+  /**
+   * @return the created flag
+   */
+  public boolean getResult() {
+    return created;
+  }
+
+}