[tracker/parser: 12/12] SPARQL: Improve group graph pattern handling

[Jürg Billeter <juergbi src gnome org>]

commit df202a528d1a166d877904434b77e912c16b3968
Author: Jürg Billeter <j bitron ch>
Date:   Fri Aug 7 15:47:20 2009 +0200

    SPARQL: Improve group graph pattern handling

 src/libtracker-data/tracker-sparql-query.vala |   80 +++++++++++--------------
 1 files changed, 34 insertions(+), 46 deletions(-)
---
diff --git a/src/libtracker-data/tracker-sparql-query.vala b/src/libtracker-data/tracker-sparql-query.vala
index d66d140..8150c77 100644
--- a/src/libtracker-data/tracker-sparql-query.vala
+++ b/src/libtracker-data/tracker-sparql-query.vala
@@ -1453,11 +1453,7 @@ public class Tracker.SparqlQuery : Object {
 		}
 	}
 
-	void visit_group_graph_pattern () throws SparqlError {
-		SourceLocation[] filters = { };
-
-		bool first_where = true;
-
+	void process_triples_block (ref bool first_where) throws SparqlError {
 		tables = new List<DataTable> ();
 		table_map = new HashTable<string,DataTable>.full (str_hash, str_equal, g_free, g_object_unref);
 
@@ -1466,25 +1462,9 @@ public class Tracker.SparqlQuery : Object {
 
 		pattern_bindings = new List<LiteralBinding> ();
 
-		int group_graph_pattern_start = (int) pattern_sql.len;
-
 		pattern_sql.append ("SELECT ");
 
-		expect (SparqlTokenType.OPEN_BRACE);
-
-		// optional TriplesBlock
-		if (current () == SparqlTokenType.VAR ||
-		    current () == SparqlTokenType.IRI_REF ||
-		    current () == SparqlTokenType.PN_PREFIX ||
-		    current () == SparqlTokenType.COLON ||
-		    current () == SparqlTokenType.OPEN_BRACKET) {
-			parse_triples_block ();
-		}
-		/* possibly
-		else {
-			pattern_sql.append ("1");
-		}
-		*/
+		parse_triples_block ();
 
 		pattern_sql.append (" FROM ");
 		bool first = true;
@@ -1567,12 +1547,35 @@ public class Tracker.SparqlQuery : Object {
 		pattern_variables = null;
 		pattern_var_map = null;
 		pattern_bindings = null;
+	}
+
+	void visit_group_graph_pattern () throws SparqlError {
+		expect (SparqlTokenType.OPEN_BRACE);
+
+		SourceLocation[] filters = { };
+
+		bool first_where = true;
+		int group_graph_pattern_start = (int) pattern_sql.len;
+
+		// optional TriplesBlock
+		if (current () == SparqlTokenType.VAR ||
+		    current () == SparqlTokenType.IRI_REF ||
+		    current () == SparqlTokenType.PN_PREFIX ||
+		    current () == SparqlTokenType.COLON ||
+		    current () == SparqlTokenType.OPEN_BRACKET) {
+			process_triples_block (ref first_where);
+		}
 
 		while (true) {
 			// check whether we have GraphPatternNotTriples | Filter
-			if (current () == SparqlTokenType.OPTIONAL ||
-			    current () == SparqlTokenType.OPEN_BRACE ||
-			    current () == SparqlTokenType.GRAPH) {
+			if (current () == SparqlTokenType.OPTIONAL) {
+				if (group_graph_pattern_start == (int) pattern_sql.len) {
+					// empty graph pattern => return one result without bound variables
+					pattern_sql.append ("SELECT 1");
+				}
+				parse_graph_pattern_not_triples (group_graph_pattern_start);
+			} else if (current () == SparqlTokenType.OPEN_BRACE ||
+			           current () == SparqlTokenType.GRAPH) {
 				parse_graph_pattern_not_triples (group_graph_pattern_start);
 			} else if (current () == SparqlTokenType.FILTER) {
 				filters += get_location ();
@@ -1587,12 +1590,17 @@ public class Tracker.SparqlQuery : Object {
 			if (current () == SparqlTokenType.VAR ||
 			    current () == SparqlTokenType.IRI_REF ||
 			    current () == SparqlTokenType.OPEN_BRACKET) {
-				parse_triples_block ();
+				process_triples_block (ref first_where);
 			}
 		}
 
 		expect (SparqlTokenType.CLOSE_BRACE);
 
+		if (group_graph_pattern_start == (int) pattern_sql.len) {
+			// empty graph pattern => return one result without bound variables
+			pattern_sql.append ("SELECT 1");
+		}
+
 		// handle filters last, they apply to the pattern as a whole
 		if (filters.length > 0) {
 			var end = get_location ();
@@ -1999,26 +2007,6 @@ public class Tracker.SparqlQuery : Object {
 				bindings.append (binding);
 			}
 			break;
-		case Rasqal.Op.BOUND:
-			pattern_sql.append ("(");
-			visit_filter (expr.arg1);
-			pattern_sql.append (") IS NOT NULL");
-			break;
-		case Rasqal.Op.REGEX:
-			pattern_sql.append ("SparqlRegex(");
-			visit_filter (expr.arg1);
-			pattern_sql.append (", ");
-			visit_filter (expr.arg2);
-			pattern_sql.append (", ");
-			if (expr.arg3 != null) {
-				visit_filter (expr.arg3);
-			} else {
-				pattern_sql.append ("''");
-			}
-			pattern_sql.append (")");
-			break;
-		default:
-			throw new SparqlError.UNSUPPORTED ("Unsupported operation");
 		}
 	}
 #endif