kotlinlang #announcements

📣 📣 📣 We are gathering some use cases and feedback in #javascript for Kotlin to JavaScript compiler. If you have plans or live project using it, please share in that channel. Thanks!

pawel_byszewski

01/12/2017, 1:34 PM

first experiment with Kotlin on Android Things:) https://github.com/Polidea/at_candle

🤖 2

jatin

01/12/2017, 2:40 PM

I have some Java code that I am trying to write in Kotlin.

jatin

01/12/2017, 2:41 PM

Java code:

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jdbc.query(sql, params, (rs, rowNum) -> {
      Set<String> labels = new LinkedHashSet<>();
      System.out.println("Row Number: " + rowNum);
      while (rs.next()) {
        String label = rs.getString("label");
        labels.add(label);
      }

      return labels;
    });

jatin

01/12/2017, 2:42 PM

However, in Kotlin, I get the same behviour from this piece of code:

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jdbc.query(sql, params) { rs, rowNum ->
            println("Row number: $rowNum")
            rs.getString("label")
        }.toSet()

jatin

01/12/2017, 2:42 PM

Does Kotlin implicitly iterate over the
rs
iterable? Because I don't need a while loop in the Kotlin version of code

orangy

01/12/2017, 2:44 PM

rs

is not an iterable, it’s a database cursor

rocketraman

01/12/2017, 2:44 PM

What is the signature of the

query

method? It probably calls the lambda with the

rs

cursor set to each row in turn.

rocketraman

01/12/2017, 2:45 PM

If that's true, then your java code is wrong

jatin

01/12/2017, 2:46 PM

Signature of

query

method:

<T> List<T> query(String sql, Map<String, ?> paramMap, RowMapper<T> rowMapper)

jatin

01/12/2017, 2:46 PM

and as Ilya mentioned,

rs

is a cursor

jatin

01/12/2017, 2:47 PM

also I am pretty sure the Java code is correct, and in the Kotlin version I do see the print statements multiple times, so it does iterate over

rs

rocketraman

01/12/2017, 2:48 PM

And what is the signature of

RowMapper

jatin

01/12/2017, 2:49 PM

@orangy Does kotlin have some specific behaviour for db cursor?

rocketraman

01/12/2017, 2:49 PM

No it doesn't

rocketraman

01/12/2017, 2:50 PM

Is it a Spring

RowMapper

? If so, the

rs

is already initialized to the current row by Spring, and the lambda should return the mapping to your object for that row only.

jatin

01/12/2017, 2:51 PM

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public interface RowMapper<T> {

	/**
	 * Implementations must implement this method to map each row of data
	 * in the ResultSet. This method should not call {@code next()} on
	 * the ResultSet; it is only supposed to map values of the current row.
	 * @param rs the ResultSet to map (pre-initialized for the current row)
	 * @param rowNum the number of the current row
	 * @return the result object for the current row
	 * @throws SQLException if a SQLException is encountered getting
	 * column values (that is, there's no need to catch SQLException)
	 */
	T mapRow(ResultSet rs, int rowNum) throws SQLException;
}

jatin

01/12/2017, 2:51 PM

It is a spring rowMapper

jatin

01/12/2017, 2:51 PM

and the docs say "This method should not call {@code next()}"