Convenience methods to serialize attributes to JSON string and other cleanup

[aarsilv]

Eppo Internal:
🎟️ Ticket 1: FF-1648 - Add more isXXX checks for EppoValue (and ideally a JSON serialize)
🎟️ Ticket 2: FF-1764 - Log "Bandit Key" in the bandit logger instead of "Variation"

For a user implementing our loggers, they will most likely need to serialize attributes to a JSON string when storing subject attributes for the assignment and subject and action numeric and categorical attributes for the bandit assignment.

This PR adds two new static utility functions to EppoAttributes:

• serializeAttributesToJSONString()
• serializeNonNullAttributesToJSONString()
  There is also a convenience instance method added to EppoAttributes:
• serializeAttributesToJSONString()

For better logger clarity, we've also renamed variation to banditKey.

Example usage by the Bandit Proxy:

private static EppoClient initClient() {
    String apiKey = dotenv.get("EPPO_SDK_KEY");
    EppoClientConfig config = EppoClientConfig.builder()
      .apiKey(apiKey)
      .assignmentLogger(assignmentLogData -> {
        String sql = "INSERT INTO bandit_test_assignments " +
          "(timestamp, flag_name, experiment_name, variation_value, subject_key, subject_attributes) " +
          "SELECT ?, ?, ?, ?, ?, parse_json(?)";

        try (PreparedStatement statement = snowflakeConnection.prepareStatement(sql)) {
          statement.setTimestamp(1, new Timestamp(assignmentLogData.timestamp.getTime()));
          statement.setString(2, assignmentLogData.featureFlag);
          statement.setNull(3, Types.NULL); // Experiment hard coded to null for now
          statement.setString(4, assignmentLogData.variation);
          statement.setString(5, assignmentLogData.subject);
          if (assignmentLogData.subjectAttributes == null) {
            statement.setNull(6, Types.NULL);
          } else {
             // 👇 USED HERE
            statement.setString(6, EppoAttributes.serializeNonNullAttributesToJSONString(assignmentLogData.subjectAttributes));
          }

          statement.executeUpdate();
          System.out.println("Logged assignment to bandit_test_assignments");
        } catch (SQLException e) {
          throw new RuntimeException("Unable to log assignment "+e.getMessage(), e);
        }
      })
      .banditLogger(banditLogData -> {
        String sql = "INSERT INTO bandit_test_bandit_assignments " +
          "(timestamp, experiment_name, variation_value, subject_key," +
          " action_name, action_probability, model_version," +
          " subject_numeric_attributes, subject_categorical_attributes," +
          " action_numeric_attributes, action_categorical_attributes) " +
          "SELECT ?, ?, ?, ?," +
          " ?, ?, ?," +
          " parse_json(?), parse_json(?)," +
          " parse_json(?), parse_json(?)";

        try (PreparedStatement statement = snowflakeConnection.prepareStatement(sql)) {
          statement.setTimestamp(1, new Timestamp(banditLogData.timestamp.getTime()));
          statement.setString(2, banditLogData.experiment);
          statement.setString(3, banditLogData.banditKey);
          statement.setString(4, banditLogData.subject);
          statement.setString(5, banditLogData.action);
          statement.setDouble(6, banditLogData.actionProbability);
          statement.setString(7, banditLogData.modelVersion);
          if (banditLogData.subjectNumericAttributes == null) {
            statement.setNull(8, Types.NULL);
          } else {
            // 👇 USED HERE
            statement.setString(8, EppoAttributes.serializeNonNullAttributesToJSONString(banditLogData.subjectNumericAttributes));
          }
          if (banditLogData.subjectCategoricalAttributes == null) {
            statement.setNull(9, Types.NULL);
          } else {
            // 👇 USED HERE
            statement.setString(9, EppoAttributes.serializeNonNullAttributesToJSONString(banditLogData.subjectCategoricalAttributes));
          }
          if (banditLogData.actionNumericAttributes == null) {
            statement.setNull(10, Types.NULL);
          } else {
            // 👇 USED HERE
            statement.setString(10, EppoAttributes.serializeNonNullAttributesToJSONString(banditLogData.actionNumericAttributes));
          }
          if (banditLogData.actionNumericAttributes == null) {
            statement.setNull(11, Types.NULL);
          } else {
            // 👇 USED HERE
            statement.setString(11, EppoAttributes.serializeNonNullAttributesToJSONString(banditLogData.actionCategoricalAttributes));
          }

          statement.executeUpdate();
          System.out.println("Logged bandit assignment to bandit_test_bandit_assignments");
        } catch (SQLException e) {
          throw new RuntimeException("Unable to log bandit assignment "+e.getMessage(), e);
        }
      })
      .build();
    return EppoClient.init(config);
  }

As part of this, knowing if an EppoValue is a boolean is useful for serializing, so we've added back in the EppoValue isXXX() methods.

[aarsilv]

Unsure yet if users will want to include or omit attributes with null values, so providing both options. (Our proxy omits them)

[aarsilv]

JSONAssert() (link to library) is pretty slick. Tests for JSON equality so you don't have to worry about things like order.

[aarsilv]

Test library for asserting JSON string equality (link)

[giorgiomartini0]

One tiny doubt; everything else looks great

[giorgiomartini0]

Maybe this was intentional and I'm missing something. I would have expected 43 here, not 43.0, to check that Java ints are serialized correctly.

[aarsilv]

The way `Maps work, I have to provide it a double 😞

[giorgiomartini0]

Ah, true. Never mind!