[rygel] tracker: More reliable duplicate subjects detection

[Zeeshan Ali Khattak <zeeshanak src gnome org>]

commit 5c2d94e5f9b8839b4f0f463d3cf9e7cabb23d3cb
Author: Zeeshan Ali (Khattak) <zeeshanak gnome org>
Date:   Tue Jul 6 20:15:51 2010 +0300

    tracker: More reliable duplicate subjects detection
    
    Instead of depending on the query/triplet builder to set the subjects to
    'null', simply compare the subjects of triplets.

 .../tracker/rygel-tracker-metadata-values.vala     |    2 +-
 .../tracker/rygel-tracker-query-triplet.vala       |   12 ++++++------
 src/plugins/tracker/rygel-tracker-query.vala       |   10 ++++++----
 3 files changed, 13 insertions(+), 11 deletions(-)
---
diff --git a/src/plugins/tracker/rygel-tracker-metadata-values.vala b/src/plugins/tracker/rygel-tracker-metadata-values.vala
index 7b30875..e5457b8 100644
--- a/src/plugins/tracker/rygel-tracker-metadata-values.vala
+++ b/src/plugins/tracker/rygel-tracker-metadata-values.vala
@@ -97,7 +97,7 @@ public class Rygel.TrackerMetadataValues : Rygel.SimpleContainer {
 
             string subject;
             if (i == 0) {
-                subject = null;
+                subject = ITEM_VARIABLE;
             } else {
                 subject = variables[i - 1];
             }
diff --git a/src/plugins/tracker/rygel-tracker-query-triplet.vala b/src/plugins/tracker/rygel-tracker-query-triplet.vala
index 5186478..e644892 100644
--- a/src/plugins/tracker/rygel-tracker-query-triplet.vala
+++ b/src/plugins/tracker/rygel-tracker-query-triplet.vala
@@ -32,15 +32,15 @@ public class Rygel.TrackerQueryTriplet {
 
     public TrackerQueryTriplet next;
 
-    public TrackerQueryTriplet (string? subject,
-                                string  predicate,
-                                string  obj) {
+    public TrackerQueryTriplet (string subject,
+                                string predicate,
+                                string obj) {
         this.subject = subject;
         this.predicate = predicate;
         this.obj = obj;
     }
 
-    public TrackerQueryTriplet.chain (string?             subject,
+    public TrackerQueryTriplet.chain (string              subject,
                                       string              predicate,
                                       TrackerQueryTriplet next) {
         this.subject = subject;
@@ -75,10 +75,10 @@ public class Rygel.TrackerQueryTriplet {
                chain_equal;
     }
 
-    public string to_string () {
+    public string to_string (bool include_subject = true) {
         string str = "";
 
-        if (this.subject != null) {
+        if (include_subject) {
             str += " " + subject;
         }
 
diff --git a/src/plugins/tracker/rygel-tracker-query.vala b/src/plugins/tracker/rygel-tracker-query.vala
index 1b3edfd..7d0a155 100644
--- a/src/plugins/tracker/rygel-tracker-query.vala
+++ b/src/plugins/tracker/rygel-tracker-query.vala
@@ -43,16 +43,18 @@ public abstract class Rygel.TrackerQuery {
 
     private string serialize_triplets (TrackerQueryTriplets triplets) {
         string str = "";
+        var include_subject = true;
 
         for (int i = 0; i < triplets.size; i++) {
-            str += triplets[i].to_string ();
+            str += triplets[i].to_string (include_subject);
 
             if (i < triplets.size - 1) {
-                if (triplets[i + 1].subject != null) {
+                include_subject = triplets[i].subject !=
+                                  triplets[i + 1].subject;
+
+                if (include_subject) {
                     str += " . ";
                 } else {
-                    // This implies that next triplet shares the subject with
-                    // this one so we need to end this one with a semi-colon.
                     str += " ; ";
                 }
             }