Fixed #7 - Keep WeakReference to parent ParseObject in ParseRelation

As suggested in the issue, keeping reference to parent objectId, className and recreating parent pointer when the parent is GC'ed. All tests passed locally.

Author: sowrabh

Parse/src/main/java/com/parse/ParseRelation.java

@@ -8,6 +8,7 @@
  */
 package com.parse;
 
+import java.lang.ref.WeakReference;
 import java.util.Collections;
 import java.util.HashSet;
 import java.util.Set;
@@ -24,7 +25,13 @@ public class ParseRelation<T extends ParseObject> {
   private final Object mutex = new Object();
 
   // The owning object of this ParseRelation.
-  private ParseObject parent;
+  private WeakReference<ParseObject> parent;
+
+  // The object Id of the parent.
+  private String parentObjectId;
+
+  // The classname of the parent to retrieve the parent ParseObject in case the parent is GC'ed.
+  private String parentClassName;
 
   // The key of the relation in the parent object.
   private String key;
@@ -36,13 +43,17 @@ public class ParseRelation<T extends ParseObject> {
   private Set<ParseObject> knownObjects = new HashSet<>();
 
   /* package */ ParseRelation(ParseObject parent, String key) {
-    this.parent = parent;
+    this.parent = new WeakReference<>(parent);
+    this.parentObjectId = parent.getObjectId();
+    this.parentClassName = parent.getClassName();
     this.key = key;
     this.targetClass = null;
   }
 
   /* package */ ParseRelation(String targetClass) {
     this.parent = null;
+    this.parentObjectId = null;
+    this.parentClassName = null;
     this.key = null;
     this.targetClass = targetClass;
   }
@@ -52,6 +63,8 @@ public class ParseRelation<T extends ParseObject> {
    */
   /* package */ ParseRelation(JSONObject jsonObject, ParseDecoder decoder) {
     this.parent = null;
+    this.parentObjectId = null;
+    this.parentClassName = null;
     this.key = null;
     this.targetClass = jsonObject.optString("className", null);
     JSONArray objectsArray = jsonObject.optJSONArray("objects");
@@ -65,12 +78,14 @@ public class ParseRelation<T extends ParseObject> {
   /* package */ void ensureParentAndKey(ParseObject someParent, String someKey) {
     synchronized (mutex) {
       if (parent == null) {
-        parent = someParent;
+        parent = new WeakReference<>(someParent);
+        parentObjectId = someParent.getObjectId();
+        parentClassName = someParent.getClassName();
       }
       if (key == null) {
         key = someKey;
       }
-      if (parent != someParent) {
+      if (parent.get() != someParent) {
         throw new IllegalStateException(
             "Internal error. One ParseRelation retrieved from two different ParseObjects.");
       }
@@ -92,7 +107,7 @@ public void add(T object) {
       ParseRelationOperation<T> operation =
           new ParseRelationOperation<>(Collections.singleton(object), null);
       targetClass = operation.getTargetClass();
-      parent.performOperation(key, operation);
+      getParent().performOperation(key, operation);
 
       knownObjects.add(object);
     }
@@ -109,7 +124,7 @@ public void remove(T object) {
       ParseRelationOperation<T> operation =
           new ParseRelationOperation<>(null, Collections.singleton(object));
       targetClass = operation.getTargetClass();
-      parent.performOperation(key, operation);
+      getParent().performOperation(key, operation);
 
       knownObjects.remove(object);
     }
@@ -124,12 +139,12 @@ public ParseQuery<T> getQuery() {
     synchronized (mutex) {
       ParseQuery.State.Builder<T> builder;
       if (targetClass == null) {
-        builder = new ParseQuery.State.Builder<T>(parent.getClassName())
+        builder = new ParseQuery.State.Builder<T>(parentClassName)
             .redirectClassNameForKey(key);
       } else {
         builder = new ParseQuery.State.Builder<>(targetClass);
       }
-      builder.whereRelatedTo(parent, key);
+      builder.whereRelatedTo(getParent(), key);
       return new ParseQuery<>(builder);
     }
   }
@@ -193,7 +208,13 @@ public ParseQuery<T> getQuery() {
   }
 
   /* package for tests */ ParseObject getParent() {
-    return parent;
+    if(parent == null){
+      return null;
+    }
+    if(parent.get() == null){
+      return ParseDecoder.get().decodePointer(parentClassName, parentObjectId);
+    }
+    return parent.get();
   }
 
   /* package for tests */ String getKey() {