find in MongoCollection

Question

I have a MongoCollection<Document> in which I assign a collection. I'm trying to find a user by his id.

user = (Document) usersCollection.find(new Document("_id", username));

with that I'm getting an error

java.lang.ClassCastException: com.mongodb.FindIterableImpl cannot be cast to org.bson.Document

When I try

    BasicDBObject query = new BasicDBObject(); 
    BasicDBObject fields = new BasicDBObject("_id", username);
    usersCollection.find(query, fields);

I'm getting an error

The method find(Bson, Class) in the type MongoCollection is not applicable for the arguments (BasicDBObject, BasicDBObject)

score 18 · Accepted Answer · edited Apr 28 '20 at 21:52

18

Try to create a filter to pass to the find() method to get a subset of the documents in your collection. For example, to find the document for which the value of the _id field is test, you would do the following:

import static com.mongodb.client.model.Filters.*;

MongoClient client = new MongoClient();
MongoDatabase database = client.getDatabase("mydb");
MongoCollection<Document> collection = database.getCollection("mycoll");
Document myDoc = collection.find(eq("_id", "test")).first();
System.out.println(myDoc.toJson());

edited Apr 28 '20 at 21:52

user_1330

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answered Jun 03 '15 at 16:23

chridam

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Where can I find eq() operator? – Darshan Puranik Nov 02 '17 at 06:50
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@DarshanPuranik `import static com.mongodb.client.model.Filters.eq;` – Woland Nov 02 '17 at 17:58
@DarshanPuranik `eq()` is a static method and on hover of static methods, Eclipse does not give an import suggestion. In this case you need to explicitly add the import statement and also for all the other similar methods. – Nisarg Patil Dec 03 '17 at 06:41
here what is the type of myDoc? – Srikanth Apr 28 '20 at 08:46
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@Srikanth `Document` – user_1330 Apr 28 '20 at 16:47

score 1 · Answer 2 · answered Jan 03 '17 at 09:54

Your issue is that you assume that the find() method returns a single Document. It doesn't. It returns a list of them.

In MongoDB 2 Java driver there was a method on the DBCollection class named findOne(). In the MongoDB 3 Java driver API, the findOne() method isn't there. So your new code for finding exactly one document becomes similar too this one:

collection.find(eq("_id", 3)).first()

where eq("_id", 3) is called a filter on your collection.

score 0 · Answer 3 · edited Jul 03 '19 at 16:35

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MongoCollection<Document> filterCriteriaDoc = mongoDatabase.getCollection("documentName");

Document filterDoc = new Document();

filterDoc.put("col1", "value");

filterDoc.append("col2", "value");

filterDoc.append("col2", "value");

Iterator<Document> iter = filterCriteriaDoc.find(filterDoc).iterator();

iter.next() can give you document .

edited Jul 03 '19 at 16:35

heilerich

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answered Jul 03 '19 at 16:24

Minal

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Please put code blocks between fences to make it more readable and enable syntax highlighting. – heilerich Jul 03 '19 at 16:29
yeah sure will do that – Minal Jul 03 '19 at 16:31

Vladi · Answer 4 · 2020-11-11T15:40:27.953

If you using IP to connect to MongoDb here how you do it change HEREYOURIP

import static com.mongodb.client.model.Filters.eq;

public static Document GetDocumentFromDataBase(String dataBase,String DBcollection,String field, String value) {
MongoClient mongoClient = new MongoClient(  " HEREYOURIP ",27017 );
MongoDatabase database =  mongoClient.getDatabase(dataBase);
MongoCollection<Document> collection = database.getCollection(DBcollection);
Document myDoc = collection.find(eq(field, value)).first();
    mongoClient.close();
    return myDoc;}

edited found other way do it

public static String GetFromDB(String DATABASE_NAME,String collectionName, String field, String value) {
        String valueBack;
        BasicDBObject whereQuery = new BasicDBObject();
        whereQuery.put("_id", new ObjectId(value));
        
        MongoClient mongoClient = new MongoClient(System.getenv("HERE_YOUR_DB_IP"), 27017);
        MongoDatabase database = mongoClient.getDatabase(DATABASE_NAME);
        MongoCollection<Document> collection = database.getCollection(collectionName);
        Document myDoc = collection.find(whereQuery).first();
        if (myDoc != null) {

            valueBack = myDoc.toString();
            mongoClient.close();
            return valueBack;
        }
        mongoClient.close();
        return null;

    }

score -2 · Answer 5 · answered Jun 03 '15 at 16:42

Do this -

 MongoClient client = new MongoClient();
    DBObject resultObject  = new BasicDBObject("_id", username);
    MongoDatabase database = client.getDatabase("DBNAME");
    MongoCollection<Document> collection =  database.getCollection("COLLECTION_NAME");
    DBObject dbObject  = new BasicDBObject("_id", username);
    resultObject   = collection.find(dbObject).next();
    String result =  resultObject.get(YOUR_COLOUM_NAME);

find in MongoCollection

5 Answers5

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