java.lang.ClassCastException: com.mongodb.client.internal.AggregateIterableImpl cannot be cast to java.util.ArrayList

Question

I have got below document . I need to match with the requestParam System Bob with the below collection and need to get the result value if requestParam matches with the Email Systems.Bob.System.

Here RequestParam is system

{ 
    "_id" : ObjectId("5f0890e870e631865877e"), 
    "user" : "testuser", 
    "Email" : "[email protected]", 
    "Batch Systems" : [
        "STAR", 
        "STORY", 
        "ITEMS",    
    ], 
    "Email Systems" : [
        {
            "Bob" : {
                "System" : "Bob", 
                **"result"** : true
            }
        }, 
        {
            "Wild" : {
                "System" : "Wild", 
                "result" : true
            }
        },
        {
            "CRaft" : {
                "System" : "Craft", 
                "result" : false
            }
        }
    ]
}

I have tried with the below syntax , getting the java.lang.ClassCastException: com.mongodb.client.internal.AggregateIterableImpl cannot be cast to java.util.ArrayList . Can anyone tell me what is wrong with the below code and help me with the synatx .

MongoDatabase database = this.mongoClient.getDatabase(this.database);
    MongoCollection<Document> user = database.getCollection(COLLECTION);
    Document userQuery = new Document();
    String searchString = new String(system);
    AggregateIterable<Document> user1 =users.aggregate((List<? extends Bson>) new Document("$project",
                new Document("Email Systems",
                        new Document("$match",
                                new Document("Email  Systems.BobSystem",searchString)))));

Milgo · Accepted Answer · 2020-09-01 08:17:21Z

1

The object returned by users.aggregate() is an AggregateIterable. ArrayList does not implement this interface so your cast fails. Try to cast and work with it as an AggregateIterable or AggregateIterableImpl.

answered Sep 1, 2020 at 8:17

Milgo

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4 Comments

Rose Over a year ago

I have tried AggregateIterable also it is giving java.lang.ClassCastException: org.bson.Document cannot be cast to java.util.List AggregateIterable<Document> user1 =users.aggregate((List<? extends Bson>) new Document("$project", new Document("Claim Systems", new Document("$match", new Document("Claim Systems.AtlasSystem",searchString)))));

Rose Over a year ago

Is there anything wrong with Java synatx , anyother way to get the result value

Milgo Over a year ago

You added an other false cast, try to avoid any, e.g.: AggregateIterable doc = users.aggregate(Collections.singletonList(...));

Rose Over a year ago

I tried below syntax AggregateIterable<Document> user1 =users.aggregate((List<? extends Bson>) new Document("$project", new Document("Claim Systems", new Document("$match", new Document("Claim Systems.AtlasSystem",searchString))))); .It is aslo giving same exception

Issam El-atif · Accepted Answer · 2020-09-03 12:52:14Z

1

users.aggregate() return an AggregateIterable and not an ArrayList hence the error. You can create an Iterator from AggregateIterable and then add documents to an ArrayList.

MongoDatabase database = this.mongoClient.getDatabase(this.database);
MongoCollection<Document> user = database.getCollection(COLLECTION);
Document userQuery = new Document();
String searchString = new String(system);
AggregateIterable aggregateIterable = users.aggregate(Collections.singletonList(new Document("$project", new Document("Email Systems", new Document("$match", new Document("Email Systems.Bob.System", searchString))))));
// Create an iterator from the iterable
Iterator iterator = aggregateIterable.iterator();
ArrayList<Document> documents = new ArrayList();
// Then iterate over the iterator
while (iterator.hasNext()) {
    documents.add((Document) iterator.next());
}

See MongoDB aggregation with Java driver for detailled answer per driver version

edited Sep 3, 2020 at 12:52

answered Sep 1, 2020 at 8:49

Issam El-atif

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8 Comments

Rose Over a year ago

Thanks for your suggestion @Issam ,I have tried as suggested but getting below exception .' Unrecognized expression '$match

Issam El-atif Over a year ago

Welcome. I see that you have edited your question after i posted my answer. Is it working for you now?

Rose Over a year ago

Still facing an issue.Getting an exception casting exception java.lang.ClassCastException: org.bson.Document cannot be cast to java.util.List .One more Query I have ,Do we need to add Documents if we want to get the 'N' of Systems value

Issam El-atif Over a year ago

You are trying to cast a Document to List with this (List<? extends Bson>) hence the error. Have a look here stackoverflow.com/questions/31643109/… it might help.

Rose Over a year ago

Thanks a lot for sharing the link .It helped a lot .And I changed the synatx as below AggregateIterable<Document> aggregateIterable = users.aggregate(Arrays.asList(new Document("$project", new Document("Claim Systems", new Document("$match", new Document("Claim Systems.Atlas", searchString)))))); Iterator iterator = aggregateIterable.iterator(); ArrayList<Document> documents = new ArrayList(); // Then iterate over the iterator while (iterator.hasNext()) { documents.add((Document) iterator.next()); }/

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