MongoDao.java 文件源码

/**
 * 统计频数
 *
 * @param collectionName
 * @param match
 * @param distinctField
 * @return
 */
public int distinctCount(String collectionName, Document match, String distinctField) {
    AggregateIterable<Document> aggregate = getDB().getCollection(collectionName).aggregate(
            Arrays.asList(
                    match(match)
                    , group(null, addToSet("_array", "$" + distinctField))
                    , project(new Document("_num", new Document("$size", "$_array")))
            )
    );
    Document first = aggregate.first();
    if (first != null) {
        return first.getInteger("_num");
    }
    return 0;
}