Postgresql array_agg of multiple columns with JDBC

Question

I'm trying to join a table that might have multiple entries for the given id and aggregate the rows corresponding to this id in an array. This looks as follows in the SQL query:

SELECT * from data
LEFT JOIN (select id, array_agg(row(foo, bar)) AS foo_bar_data from foo_bar_table group by id) AS temp using(id)

This works as intended, but I'm having trouble reading out the result in JDBC.

ResultSet rs = st.executeQuery(...)
Array a = rs.getArray("foo_bar_data")
// Now I want to iterate over the array, reading the values foo and bar of each item.

My efforts so far always ended in a Method org.postgresql.jdbc4.Jdbc4Array.getArrayImpl(long,int,Map) is not yet implemented. exception. How can I iterate over a, retrieving the values foo and bar?

Edit: I should possibly also mention, that foo and bar don't have the same type.

Answer 1

Postgres JDBC driver does not support anything except basic types (numbers, date/timestamp, string) as JDBC array. You can call array_agg twice and get two arrays on each row:

    try (Connection db = DriverManager.getConnection("jdbc:postgresql://localhost:5432/postgres", "postgres", "postgres");
                 ResultSet rs = db.createStatement().executeQuery("select array_agg(i), array_agg(s) from (select 1 i, 'a' s union select 2 i, 'b' s) t")) {
        rs.next();
        System.out.println(Arrays.toString((Object[]) rs.getArray(1).getArray()));
        System.out.println(Arrays.toString((Object[]) rs.getArray(2).getArray()));
    }