Fixed issue #2309 wit new functions to get traversed elements

We'd need 3 new functions:

traversedVertex, to return the traversed vertex
traversedEdge, to return the traversed edge
traversedElement, to return any of the traversed element
All functions should get 2 params:

index, as starting index. negative numbers means from the end, positive
from the beginning of the stack. Example 0 = absolute first traversed
vertex, -1 = relative last one
items, as optional, by default is 1, but specifying >1 collects the
elements in a collection.
Example:

select $path, traversedVertex(-1) from ( traverse out() from #9:1 while
$depth < 10 )

core/src/main/java/com/orientechnologies/orient/core/sql/functions/ODefaultSQLFunctionFactory.java

@@ -15,6 +15,10 @@
  */
 package com.orientechnologies.orient.core.sql.functions;
 
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Set;
+
 import com.orientechnologies.orient.core.exception.OCommandExecutionException;
 import com.orientechnologies.orient.core.sql.functions.coll.*;
 import com.orientechnologies.orient.core.sql.functions.geo.OSQLFunctionDistance;
@@ -33,10 +37,6 @@
 import com.orientechnologies.orient.core.sql.functions.misc.OSQLFunctionSysdate;
 import com.orientechnologies.orient.core.sql.functions.text.OSQLFunctionFormat;
 
-import java.util.HashMap;
-import java.util.Map;
-import java.util.Set;
-
 /**
  * Default set of SQL function.
  * 
@@ -60,6 +60,9 @@ public final class ODefaultSQLFunctionFactory implements OSQLFunctionFactory {
     register(OSQLFunctionEval.NAME, OSQLFunctionEval.class);
     register(OSQLFunctionFirst.NAME, OSQLFunctionFirst.class);
     register(OSQLFunctionFormat.NAME, new OSQLFunctionFormat());
+    register(OSQLFunctionTraversedEdge.NAME, OSQLFunctionTraversedEdge.class);
+    register(OSQLFunctionTraversedElement.NAME, OSQLFunctionTraversedElement.class);
+    register(OSQLFunctionTraversedVertex.NAME, OSQLFunctionTraversedVertex.class);
     register(OSQLFunctionIf.NAME, new OSQLFunctionIf());
     register(OSQLFunctionIfNull.NAME, new OSQLFunctionIfNull());
     register(OSQLFunctionIntersect.NAME, OSQLFunctionIntersect.class);

core/src/main/java/com/orientechnologies/orient/core/sql/functions/coll/OSQLFunctionLast.java

@@ -51,7 +51,7 @@ public Object execute(Object iThis, final OIdentifiable iCurrentRecord, Object i
   }
 
   public boolean aggregateResults() {
-    return configuredParameters.length == 1;
+    return false;
   }
 
   @Override

core/src/main/java/com/orientechnologies/orient/core/sql/functions/coll/OSQLFunctionTraversedEdge.java

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2010-2012 Luca Garulli (l.garulli--at--orientechnologies.com)
+ *
+ * Licensed 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.
+ */
+package com.orientechnologies.orient.core.sql.functions.coll;
+
+import com.orientechnologies.orient.core.command.OCommandContext;
+import com.orientechnologies.orient.core.db.record.OIdentifiable;
+
+/**
+ * Returns a traversed element from the stack. Use it with SQL traverse only.
+ * 
+ * @author Luca Garulli (l.garulli--at--orientechnologies.com)
+ * 
+ */
+public class OSQLFunctionTraversedEdge extends OSQLFunctionTraversedElement {
+  public static final String NAME = "traversedEdge";
+
+  public OSQLFunctionTraversedEdge() {
+    super(NAME);
+  }
+
+  public Object execute(Object iThis, final OIdentifiable iCurrentRecord, Object iCurrentResult, final Object[] iParams,
+      final OCommandContext iContext) {
+    return evaluate( iParams, iContext, "E" );
+  }
+}

core/src/main/java/com/orientechnologies/orient/core/sql/functions/coll/OSQLFunctionTraversedElement.java

@@ -0,0 +1,124 @@
+/*
+ * Copyright 2010-2012 Luca Garulli (l.garulli--at--orientechnologies.com)
+ *
+ * Licensed 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.
+ */
+package com.orientechnologies.orient.core.sql.functions.coll;
+
+import com.orientechnologies.orient.core.command.OCommandContext;
+import com.orientechnologies.orient.core.command.traverse.OTraverseRecordProcess;
+import com.orientechnologies.orient.core.db.record.OIdentifiable;
+import com.orientechnologies.orient.core.exception.OCommandExecutionException;
+import com.orientechnologies.orient.core.record.impl.ODocument;
+import com.orientechnologies.orient.core.sql.functions.OSQLFunctionConfigurableAbstract;
+
+import java.util.ArrayDeque;
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.List;
+
+/**
+ * Returns a traversed element from the stack. Use it with SQL traverse only.
+ * 
+ * @author Luca Garulli (l.garulli--at--orientechnologies.com)
+ * 
+ */
+public class OSQLFunctionTraversedElement extends OSQLFunctionConfigurableAbstract {
+  public static final String NAME = "traversedElement";
+
+  public OSQLFunctionTraversedElement(final String name) {
+    super(name, 1, 2);
+  }
+
+  public boolean aggregateResults() {
+    return false;
+  }
+
+  @Override
+  public Object getResult() {
+    return null;
+  }
+
+  @Override
+  public boolean filterResult() {
+    return true;
+  }
+
+  public String getSyntax() {
+    return getName() + "(<beginIndex> [,<items>])";
+  }
+
+  public Object execute(Object iThis, final OIdentifiable iCurrentRecord, Object iCurrentResult, final Object[] iParams,
+      final OCommandContext iContext) {
+    return evaluate(iParams, iContext, null);
+  }
+
+  protected Object evaluate(final Object[] iParams, final OCommandContext iContext, final String iClassName) {
+    final int beginIndex = (Integer) iParams[0];
+    final int items = iParams.length > 1 ? (Integer) iParams[1] : 1;
+
+    final ArrayDeque stack = (ArrayDeque) iContext.getVariable("stack");
+    if (stack == null)
+      throw new OCommandExecutionException("Cannot invoke " + getName() + "() against non traverse command");
+
+    final List<OIdentifiable> result = items > 1 ? new ArrayList<OIdentifiable>(items) : null;
+
+    if (beginIndex < 0) {
+      int i = -1;
+      for (Iterator it = stack.iterator(); it.hasNext();) {
+        final Object o = it.next();
+        if (o instanceof OTraverseRecordProcess) {
+          final ODocument record = ((OTraverseRecordProcess) o).getTarget();
+
+          if (iClassName == null || record.getSchemaClass().isSubClassOf(iClassName)) {
+            if (i <= beginIndex) {
+              if (items == 1)
+                return record;
+              else {
+                result.add(record);
+                if (result.size() >= items)
+                  break;
+              }
+            }
+            i--;
+          }
+        }
+      }
+    } else {
+      int i = 0;
+      for (Iterator it = stack.descendingIterator(); it.hasNext();) {
+        final Object o = it.next();
+        if (o instanceof OTraverseRecordProcess) {
+          final ODocument record = ((OTraverseRecordProcess) o).getTarget();
+
+          if (iClassName == null || record.getSchemaClass().isSubClassOf(iClassName)) {
+            if (i >= beginIndex) {
+              if (items == 1)
+                return record;
+              else {
+                result.add(record);
+                if (result.size() >= items)
+                  break;
+              }
+            }
+            i++;
+          }
+        }
+      }
+    }
+
+    if (items > 0 && result != null && !result.isEmpty())
+      return result;
+    return null;
+  }
+}

core/src/main/java/com/orientechnologies/orient/core/sql/functions/coll/OSQLFunctionTraversedVertex.java

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2010-2012 Luca Garulli (l.garulli--at--orientechnologies.com)
+ *
+ * Licensed 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.
+ */
+package com.orientechnologies.orient.core.sql.functions.coll;
+
+import com.orientechnologies.orient.core.command.OCommandContext;
+import com.orientechnologies.orient.core.db.record.OIdentifiable;
+
+/**
+ * Returns a traversed element from the stack. Use it with SQL traverse only.
+ * 
+ * @author Luca Garulli (l.garulli--at--orientechnologies.com)
+ * 
+ */
+public class OSQLFunctionTraversedVertex extends OSQLFunctionTraversedElement {
+  public static final String NAME = "traversedVertex";
+
+  public OSQLFunctionTraversedVertex() {
+    super(NAME);
+  }
+
+  public Object execute(Object iThis, final OIdentifiable iCurrentRecord, Object iCurrentResult, final Object[] iParams,
+      final OCommandContext iContext) {
+    return evaluate( iParams, iContext, "V" );
+  }
+}