libtracker-data: Add support for BIND

The BIND form allows a value to be assigned to a variable from a graph
pattern:

  SELECT ?u ?hour
  { ?u a rdfs:Resource .
       nfo:fileLastModified ?modified
    BIND (HOUR (?modified) AS ?hour)
  }

It will be specially useful on places where we use the result of a
calculation on more than one places, eg. on SELECT and FILTER(). It will
also be useful combined with DELETE...INSERT...WHERE to perform complex
mass-updates in a single query.

http://www.w3.org/TR/sparql11-query/#bind

2 files changed, 34 insertions, 1 deletions

diff --git a/src/libtracker-data/tracker-sparql-pattern.vala b/src/libtracker-data/tracker-sparql-pattern.vala
index 7dfbcd44a..ec9d5471e 100644
--- a/src/libtracker-data/tracker-sparql-pattern.vala
+++ b/src/libtracker-data/tracker-sparql-pattern.vala
@@ -1102,6 +1102,28 @@ class Tracker.Sparql.Pattern : Object {
 
 				current_graph = old_graph;
 				current_graph_is_var = old_graph_is_var;
+			} else if (accept (SparqlTokenType.BIND)) {
+				var binding = new VariableBinding ();
+				var bind_sql = new StringBuilder ();
+
+				expect (SparqlTokenType.OPEN_PARENS);
+
+				expression.translate_expression (bind_sql);
+				binding.sql_expression = bind_sql.str;
+
+				expect (SparqlTokenType.AS);
+				expect (SparqlTokenType.VAR);
+
+				var as_var = context.get_variable (get_last_string ().substring (1));
+
+				if (as_var.binding != null) {
+					throw query.get_internal_error ("Expected undefined variable in BIND alias");
+				}
+
+				binding.variable = as_var;
+				add_variable_binding (sql, binding, VariableState.BOUND);
+
+				expect (SparqlTokenType.CLOSE_PARENS);
 			} else if (current () == SparqlTokenType.OPEN_BRACE) {
 				if (!in_triples_block && !in_group_graph_pattern) {
 					in_group_graph_pattern = true;
diff --git a/src/libtracker-data/tracker-sparql-scanner.vala b/src/libtracker-data/tracker-sparql-scanner.vala
index f23ba0ad2..e3705609b 100644
--- a/src/libtracker-data/tracker-sparql-scanner.vala
+++ b/src/libtracker-data/tracker-sparql-scanner.vala
@@ -159,7 +159,16 @@ public class Tracker.SparqlScanner : Object {
 			switch (begin[0]) {
 			case 'B':
 			case 'b':
-				if (matches (begin, "BASE")) return SparqlTokenType.BASE;
+				switch (begin[1]) {
+				case 'A':
+				case 'a':
+					if (matches (begin, "BASE")) return SparqlTokenType.BASE;
+					break;
+				case 'I':
+				case 'i':
+					if (matches (begin, "BIND")) return SparqlTokenType.BIND;
+					break;
+				}
 				break;
 			case 'C':
 			case 'c':
@@ -1021,6 +1030,7 @@ public enum Tracker.SparqlTokenType {
 	AVG,
 	BASE,
 	BLANK_NODE,
+	BIND,
 	BOUND,
 	BY,
 	CEIL,
@@ -1148,6 +1158,7 @@ public enum Tracker.SparqlTokenType {
 		case AVG: return "`AVG'";
 		case BASE: return "`BASE'";
 		case BLANK_NODE: return "blank node";
+		case BIND: return "`BIND'";
 		case BOUND: return "`BOUND'";
 		case BY: return "`BY'";
 		case CEIL: return "`CEIL'";