Finding distinct from collections in mongodb

Question

Our previous implementation for finding distinct elements from a collection used to be :

List<String> names = mongoClient.getDB(dbName).getCollection(collectionName).distinct(NAME_KEY);

Trying to upgrade this into the current implementation with mongo 3.3.0+ as tried is :

List<String> names = mongoClient.getDatabase(dbName)
                        .getCollection(collectionName, TDocType.class)
                        .distinct(NAME_KEY, String.class); // compile error - required Class<TResult>

Have also given a try to

.distinct(NAME_KEY, TDocType.class)  // doesn't work

What shall be the target type of the iterable in this case?

Edit - The question is not a duplicate of Get distinct records values since the implementation has changed over the upgrade of mongodb-java-driver.

score 8 · Accepted Answer · edited Jul 19 '23 at 08:04

8

Improved answer from @jyemin

List<String> list = mongoClient.getDatabase(dbName)
                .getCollection(collectionName, TDocType.class)
                .distinct(NAME_KEY, String.class)
                .into(new ArrayList<>());

Original answer

You can try something like this.

DistinctIterable<String> iterable = mongoClient.getDatabase(dbName).
            .getCollection(collectionName, TDocType.class).distinct(NAME_KEY, String.class);
MongoCursor<String> cursor = iterable.iterator();
List<String> list = new ArrayList<>();
while (cursor.hasNext()) {
    list.add(cursor.next());
 }

edited Jul 19 '23 at 08:04

takanuva15

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answered Oct 25 '16 at 17:55

s7vr

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Thanks. Also this can be further improved as `for(String str : iterable) { list.add(str); }` instead of using Cursor above. The way I am using it is `List list = Lists.newArrayList(mongoClient.getDatabase(dbName).getCollection(collectionName, TDocType.class).distinct(NAME_KEY, String.class));` where the `Lists` is from google collection. – Naman Oct 27 '16 at 17:43
7

Or more simply: List list = mongoClient.getDatabase(dbName).getCollection(collectionName, TDocType.class).distinct(NAME_KEY, String.class).into(new ArrayList<>()); – jyemin Nov 11 '16 at 20:18

score 0 · Answer 2 · answered May 25 '23 at 16:15

for those who already have org.codehaus.groovy:groovy in their deps :

// import static org.codehaus.groovy.runtime.DefaultGroovyMethods.toSet;.
toSet(distinctIterable);

Example

DistinctIterable<String> distinctIterable = getCollection()
            .distinct(FIELD_ID, query.getQueryObject(), String.class);
return toSet(distinctIterable);

Finding distinct from collections in mongodb

2 Answers2

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