[mongodb] Permission optimization of single database is specified (#1240)

flink-connector-mongodb-cdc/src/main/java/com/ververica/cdc/connectors/mongodb/internal/MongoDBConnectorSourceTask.java

@@ -303,12 +303,16 @@ public class MongoDBConnectorSourceTask extends SourceTask {
 
                 Bson nsFilter = regex(ADD_NS_FIELD_NAME, namespacesRegex);
                 if (databaseList != null) {
-                    String databaseRegex =
-                            includeListAsPatterns(databaseList).stream()
-                                    .map(Pattern::pattern)
-                                    .collect(Collectors.joining("|"));
-                    Bson dbFilter = regex("ns.db", databaseRegex);
-                    nsFilter = and(dbFilter, nsFilter);
+                    if (isIncludeListExplicitlySpecified(databaseList, discoveredDatabases)) {
+                        props.put(MongoSourceConfig.DATABASE_CONFIG, discoveredDatabases.get(0));
+                    } else {
+                        String databaseRegex =
+                                includeListAsPatterns(databaseList).stream()
+                                        .map(Pattern::pattern)
+                                        .collect(Collectors.joining("|"));
+                        Bson dbFilter = regex("ns.db", databaseRegex);
+                        nsFilter = and(dbFilter, nsFilter);
+                    }
                 }
                 pipeline.add(match(nsFilter));