Save reference to document in rocket

core/src/main/java/info/openrocket/core/document/OpenRocketDocument.java

@@ -110,6 +110,7 @@ public class OpenRocketDocument implements ComponentChangeListener, StateChangeL
 	 */
 	OpenRocketDocument(Rocket rocket) {
 		this.rocket = rocket;
+		rocket.setDocument(this);
 		this.objOptions = prefs.loadOBJExportOptions(rocket);
 		rocket.enableEvents();
 		init();

core/src/main/java/info/openrocket/core/rocketcomponent/Rocket.java

@@ -3,6 +3,7 @@ package info.openrocket.core.rocketcomponent;
 import java.util.*;
 import java.util.concurrent.ConcurrentHashMap;
 
+import info.openrocket.core.document.OpenRocketDocument;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -51,6 +52,7 @@ public class Rocket extends ComponentAssembly {
 
 	private boolean eventsEnabled = false;
 
+	private OpenRocketDocument document;
 	private ReferenceType refType = ReferenceType.MAXIMUM; // Set in constructor
 	private double customReferenceLength = DEFAULT_REFERENCE_LENGTH;
 	
@@ -191,7 +193,23 @@ public class Rocket extends ComponentAssembly {
 	public int getFunctionalModID() {
 		return functionalModID;
 	}
-	
+
+	/**
+	 * Return the OpenRocketDocument that this rocket is part of, or null if it is not part of any document.
+	 * @return the document, or null
+	 */
+	public OpenRocketDocument getDocument() {
+		return document;
+	}
+
+	/**
+	 * Set the OpenRocketDocument that this rocket is part of.
+	 * @param document the document
+	 */
+	public void setDocument(OpenRocketDocument document) {
+		this.document = document;
+	}
+
 	public Collection<AxialStage> getStageList() {
 		return this.stageMap.values();
 	}