Improve exception message when replace would modify the _id

Author: bwaldvogel

core/src/main/java/de/bwaldvogel/mongo/backend/AbstractMongoCollection.java

@@ -457,7 +457,7 @@ public Document findAndModify(Document query) {
         return result;
     }
 
-    private static class FindAndModifyPlanExecutorError extends MongoServerError {
+    public static class FindAndModifyPlanExecutorError extends MongoServerError {
 
         private static final long serialVersionUID = 1L;
 
@@ -466,6 +466,11 @@ private static class FindAndModifyPlanExecutorError extends MongoServerError {
         private FindAndModifyPlanExecutorError(MongoServerError cause) {
             super(cause.getCode(), cause.getCodeName(), PREFIX + cause.getMessageWithoutErrorCode(), cause);
         }
+
+        @Override
+        public synchronized MongoServerError getCause() {
+            return (MongoServerError) super.getCause();
+        }
     }
 
     @Override

core/src/main/java/de/bwaldvogel/mongo/backend/aggregation/stage/MergeStage.java

@@ -13,6 +13,8 @@
 
 import de.bwaldvogel.mongo.MongoCollection;
 import de.bwaldvogel.mongo.MongoDatabase;
+import de.bwaldvogel.mongo.backend.AbstractMongoCollection.FindAndModifyPlanExecutorError;
+import de.bwaldvogel.mongo.backend.Assert;
 import de.bwaldvogel.mongo.backend.DatabaseResolver;
 import de.bwaldvogel.mongo.backend.Index;
 import de.bwaldvogel.mongo.backend.IndexKey;
@@ -220,12 +222,18 @@ private Document getJoinQuery(Document document) {
 
     private void replaceDocument(MongoCollection<?> collection, Document existingDocument, Document document) {
         Document documentSelector = new Document("_id", existingDocument.get("_id"));
-        Document result = collection.findAndModify(new Document("query", documentSelector)
-            .append("new", false)
-            .append("upsert", false)
-            .append("update", document));
-        if (!result.get("ok").equals(1.0)) {
-            throw new RuntimeException("Unexpected result: " + result);
+        try {
+            Document result = collection.findAndModify(new Document("query", documentSelector)
+                .append("new", false)
+                .append("upsert", false)
+                .append("update", document));
+            Assert.equals(result.get("ok"), 1.0);
+        } catch (FindAndModifyPlanExecutorError e) {
+            MongoServerError cause = e.getCause();
+            throw new MongoServerError(cause.getCode(), cause.getCodeName(),
+                "$merge failed to update the matching document,"
+                    + " did you attempt to modify the _id or the shard key? :: caused by :: "
+                    + cause.getMessageWithoutErrorCode(), cause);
         }
     }
 

test-common/src/main/java/de/bwaldvogel/mongo/backend/AbstractAggregationTest.java

@@ -2384,7 +2384,7 @@ void testAggregateWithMerge_stringParameter() throws Exception {
     }
 
     @Test
-    void testAggregateWithMerge_idMustNotBeModified() throws Exception {
+    void testAggregateWithMerge_idMustNotBeModified_merge() throws Exception {
         collection.insertMany(jsonList(
             "_id: 1, name: 'Ant'",
             "_id: 2, name: 'Bee'",
@@ -2409,6 +2409,32 @@ void testAggregateWithMerge_idMustNotBeModified() throws Exception {
                 "Performing an update on the path '_id' would modify the immutable field '_id''");
     }
 
+    @Test
+    void testAggregateWithMerge_idMustNotBeModified_replace() throws Exception {
+        collection.insertMany(jsonList(
+            "_id: 1, name: 'Ant'",
+            "_id: 2, name: 'Bee'",
+            "_id: 3, name: 'Cat'"
+        ));
+
+        MongoCollection<Document> otherCollection = db.getCollection("other");
+
+        otherCollection.insertMany(jsonList(
+            "_id: 10, name: 'Ant'",
+            "_id: 11, name: 'Bee'",
+            "_id: 12, name: 'Cat'"
+        ));
+
+        otherCollection.createIndex(json("name: 1"), new IndexOptions().unique(true));
+
+        assertThatExceptionOfType(MongoCommandException.class)
+            .isThrownBy(() -> collection.aggregate(jsonList("$merge : { into: 'other', on: 'name', whenMatched: 'replace' }")).first())
+            .withMessageStartingWith("Command failed with error 66 (ImmutableField): " +
+                "'PlanExecutor error during aggregation :: caused by :: " +
+                "$merge failed to update the matching document, did you attempt to modify the _id or the shard key? :: caused by :: " +
+                "After applying the update, the (immutable) field '_id' was found to have been altered to _id: 1'");
+    }
+
     @Test
     void testAggregateWithMerge_onWithoutUniqueIndex() throws Exception {
         collection.insertOne(json("_id: 1"));