From 701fffa16a9aec0e0565da12bd5da5d372f6e612 Mon Sep 17 00:00:00 2001
From: Antti Villberg <antti.villberg@semantum.fi>
Date: Thu, 9 Jan 2020 14:54:45 +0200
Subject: [PATCH] Make StandardVariableBuilder singleton

gitlab #441

Change-Id: I28bb5ccb8f5164e3bbe4f0e0c68d4b221cb35d24
---
 bundles/org.simantics.db.layer0/adapters.xml  |  3 +-
 .../variable/StandardVariableBuilder.java     | 29 +++++++++++++------
 2 files changed, 22 insertions(+), 10 deletions(-)

diff --git a/bundles/org.simantics.db.layer0/adapters.xml b/bundles/org.simantics.db.layer0/adapters.xml
index 11a3ff235..bdf1f1435 100644
--- a/bundles/org.simantics.db.layer0/adapters.xml
+++ b/bundles/org.simantics.db.layer0/adapters.xml
@@ -35,7 +35,8 @@
 
 	<target interface="org.simantics.db.layer0.variable.VariableBuilder">
 		<type uri="http://www.simantics.org/Layer0-0.0/Entity"
-			class="org.simantics.db.layer0.variable.StandardVariableBuilder" >
+			class="org.simantics.db.layer0.variable.StandardVariableBuilder"
+			constructor="get" >
 		</type>
 	</target>
 
diff --git a/bundles/org.simantics.db.layer0/src/org/simantics/db/layer0/variable/StandardVariableBuilder.java b/bundles/org.simantics.db.layer0/src/org/simantics/db/layer0/variable/StandardVariableBuilder.java
index b1af87f98..992e3e699 100644
--- a/bundles/org.simantics.db.layer0/src/org/simantics/db/layer0/variable/StandardVariableBuilder.java
+++ b/bundles/org.simantics.db.layer0/src/org/simantics/db/layer0/variable/StandardVariableBuilder.java
@@ -6,14 +6,25 @@ import org.simantics.db.exception.DatabaseException;
 
 public class StandardVariableBuilder<Node> implements VariableBuilder<Node> {
 
-	@Override
-	public Variable buildChild(ReadGraph graph, Variable parent, VariableNode<Node> node, Resource child) {
-		return new StandardGraphChildVariable(parent, node, child);
-	}
-
-	@Override
-	public Variable buildProperty(ReadGraph graph, Variable parent, VariableNode<Node> node, Resource subject, Resource predicate) throws DatabaseException {
-		return new StandardGraphPropertyVariable(graph, parent, node, subject, predicate);
-	}
+    private static StandardVariableBuilder<?> INSTANCE = null;
+
+    private StandardVariableBuilder() {}
+
+    public static synchronized StandardVariableBuilder<?> get() {
+        if(INSTANCE == null) {
+            INSTANCE = new StandardVariableBuilder<>();
+        }
+        return INSTANCE;
+    }
+
+    @Override
+    public Variable buildChild(ReadGraph graph, Variable parent, VariableNode<Node> node, Resource child) {
+        return new StandardGraphChildVariable(parent, node, child);
+    }
+
+    @Override
+    public Variable buildProperty(ReadGraph graph, Variable parent, VariableNode<Node> node, Resource subject, Resource predicate) throws DatabaseException {
+        return new StandardGraphPropertyVariable(graph, parent, node, subject, predicate);
+    }
 
 }
-- 
2.47.1