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diff --git a/bundles/org.simantics.browsing.ui.graph.impl/src/org/simantics/browsing/ui/graph/impl/LazyParametrizedViewpoint.java b/bundles/org.simantics.browsing.ui.graph.impl/src/org/simantics/browsing/ui/graph/impl/LazyParametrizedViewpoint.java
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+/*******************************************************************************
+ * Copyright (c) 2007, 2010 Association for Decentralized Information Management
+ * in Industry THTH ry.
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/legal/epl-v10.html
+ *
+ * Contributors:
+ *     VTT Technical Research Centre of Finland - initial API and implementation
+ *******************************************************************************/
+package org.simantics.browsing.ui.graph.impl;
+
+import java.util.function.Consumer;
+
+import org.simantics.browsing.ui.BuiltinKeys;
+import org.simantics.browsing.ui.DataSource;
+import org.simantics.browsing.ui.NodeContext;
+import org.simantics.browsing.ui.PrimitiveQueryUpdater;
+import org.simantics.browsing.ui.common.viewpoints.ViewpointStub;
+import org.simantics.browsing.ui.content.Viewpoint;
+import org.simantics.browsing.ui.graph.impl.request.ParametrizedResourceQuery;
+import org.simantics.db.ReadGraph;
+import org.simantics.db.exception.DatabaseException;
+import org.simantics.db.procedure.Listener;
+import org.simantics.utils.datastructures.Pair;
+
+/**
+ * Implement {@link #children(ReadGraph)} and {@link #hasChildren(ReadGraph)}.
+ * 
+ * @author Tuukka Lehtonen
+ */
+public abstract class LazyParametrizedViewpoint extends ViewpointStub {
+
+	/**
+	 * Needed for separating childQuery and hasChildQuery from each other in the
+	 * equals sense.
+	 */
+	private static final Object                              CHILDREN     = new Object();
+	private static final Object                              HAS_CHILDREN = new Object();
+
+	private final ParametrizedResourceQuery<NodeContext[]> childQuery;
+	private final ParametrizedResourceQuery<Boolean>        hasChildQuery;
+
+    private final Listener<NodeContext[]>              childQueryProcedure;
+    private final Listener<Boolean>                     hasChildQueryProcedure;
+
+    private final PrimitiveQueryUpdater                      updater;
+    private final NodeContext                               context;
+    private final BuiltinKeys.ViewpointKey                   key;
+
+	/**
+	 * @return
+	 */
+	public abstract NodeContext[] children(ReadGraph graph) throws DatabaseException;
+
+	/**
+	 * @param graph
+	 * @return
+	 */
+	public abstract Boolean hasChildren(ReadGraph graph) throws DatabaseException;
+
+
+	public LazyParametrizedViewpoint(PrimitiveQueryUpdater updater, NodeContext context, BuiltinKeys.ViewpointKey key, Object... parameters) {
+		assert updater != null;
+		assert context != null;
+		assert key != null;
+
+		this.updater = updater;
+		this.context = context;
+		this.key = key;
+
+		this.childQuery = new ParametrizedResourceQuery<NodeContext[]>(Pair.make(getClass(), CHILDREN), context, parameters) {
+
+			@Override
+			public NodeContext[] perform(ReadGraph graph) throws DatabaseException {
+				return  children(graph);
+			}
+
+		};
+
+		this.childQueryProcedure = new Listener<NodeContext[]>() {
+
+			@Override
+			public void execute(NodeContext[] result) {
+				replaceChildrenResult(result);
+			}
+
+			@Override
+			public boolean isDisposed() {
+				return LazyParametrizedViewpoint.this.updater.isDisposed();
+			}
+
+			public void exception(Throwable t) {
+				System.out.print("LazyParametrizedViewpoint2.childQuery failed: ");
+				t.printStackTrace();
+			}
+
+		};
+
+		this.hasChildQuery = new ParametrizedResourceQuery<Boolean>(Pair.make(getClass(), HAS_CHILDREN), context, parameters) {
+
+			@Override
+			public Boolean perform(ReadGraph graph) throws DatabaseException {
+				return hasChildren(graph);
+			}
+
+		};
+
+		this.hasChildQueryProcedure = new Listener<Boolean>() {
+
+			@Override
+			public void execute(Boolean result) {
+				replaceHasChildrenResult(result);
+			}
+
+			@Override
+			public boolean isDisposed() {
+				return LazyParametrizedViewpoint.this.updater.isDisposed();
+			}
+
+			public void exception(Throwable t) {
+				System.out.print("LazyParametrizedViewpoint2.hasChildQuery failed: ");
+				t.printStackTrace();
+			}
+
+		};
+
+	}
+
+	public NodeContext getContext() {
+		return context;
+	}
+
+	@Override
+	public NodeContext[] getChildren() {
+		if (children == Viewpoint.PENDING_CHILDREN) {
+			DataSource<ReadGraph> source = updater.getDataSource(ReadGraph.class);
+			if (source != null) {
+				source.schedule(graph -> graph.asyncRequest(childQuery, childQueryProcedure));
+			}
+		}
+
+		return children;
+	}
+
+	@Override
+	public Boolean getHasChildren() {
+		if (hasChildren == Viewpoint.PENDING_HAS_CHILDREN) {
+			DataSource<ReadGraph> source = updater.getDataSource(ReadGraph.class);
+			if (source != null) {
+				source.schedule(new Consumer<ReadGraph>() {
+					@Override
+					public void accept(ReadGraph source) {
+						source.asyncRequest(hasChildQuery, hasChildQueryProcedure);
+					}
+				});
+			}
+		}
+
+		return hasChildren;
+	}
+
+	protected void replaceChildrenResult(NodeContext[] result) {
+		setChildren(updater, result);
+		updater.scheduleReplace(context, key, this);
+	}
+
+	protected void replaceHasChildrenResult(Boolean result) {
+		setHasChildren(result);
+		updater.scheduleReplace(context, key, this);
+	}
+
+	/**
+	 * @param <T>
+	 * @param clazz
+	 * @return input of the specified class
+	 * @throws ClassCastException if the input class does not match the
+	 *         specified class
+	 * @throws NullPointerException if the input is null
+	 */
+	 protected <T> T getInput(Class<T> clazz) throws ClassCastException {
+		 Object o = context.getConstant(BuiltinKeys.INPUT);
+		 if (o == null)
+			 throw new NullPointerException("null input");
+		 return clazz.cast(o);
+	 }
+
+	 /**
+	  * @param <T>
+	  * @param clazz
+	  * @return <code>null</code> if input is <code>null</code> or if the class does not match
+	  */
+	 protected <T> T tryGetInput(Class<T> clazz) {
+		 Object o = context.getConstant(BuiltinKeys.INPUT);
+		 if (o != null && clazz.isInstance(o))
+			 return clazz.cast(o);
+		 return null;
+	 }
+
+}