Fix Rails 7.2 JSONB pluck type casting

[rajaravivarma-r]

Rails 7.2 started reading AR::Result column types by index during pluck, but PostgreSQLResult only stored types by column name. As a result, JSONB expressions like payload -> 'fields' exposed a named type while column_types[0] stayed nil, and pluck returned raw strings instead of cast JSON values.

Store PostgreSQL result types under both the column name and zero-based column index, and add regression coverage for JSONB array/object/scalar extraction across multiple rows in types_test.

Behaviour examples

This change restores the behaviour we had in earlier Rails / ActiveRecord-JDBC versions, where pluck on JSONB SQL fragments returned type-cast Ruby values instead of raw JSON strings.

Example 1: JSONB array extraction

PostgresqlJsonb.pluck(Arel.sql("payload -> 'fields'"))

Expected behaviour in previous Rails / AR-JDBC versions, and with this change:

[
  [{ "id" => "fld1", "name" => "Name", "type" => "singleLineText" }],
  [{ "id" => "fld2", "name" => "Title", "type" => "number" }]
]

Type-wise, that is:

PostgresqlJsonb.pluck(Arel.sql("payload -> 'fields'")).map(&:class)
# => [Array, Array]

Behaviour seen on Rails 7.2 before this fix:

PostgresqlJsonb.pluck(Arel.sql("payload -> 'fields'")).map(&:class)
# => [String, String]

Example 2: JSONB scalar extraction

PostgresqlJsonb.pluck(Arel.sql("payload -> 'profile' -> 'age'"))

Expected behaviour in previous Rails / AR-JDBC versions, and with this change:

[25, 40]

Type-wise, that is:

PostgresqlJsonb.pluck(Arel.sql("payload -> 'profile' -> 'age'")).map(&:class)
# => [Integer, Integer]

Behaviour seen on Rails 7.2 before this fix:

PostgresqlJsonb.pluck(Arel.sql("payload -> 'profile' -> 'age'"))
# => ["25", "40"]

Internally, the issue was that AR-JDBC exposed the JSONB type under the column name, but Rails 7.2 started reading AR::Result#column_types by column index during pluck. This change stores the type under both the column name and the zero-based column index, so JSONB fragments are cast correctly again.

[rajaravivarma-r]

After upgrading from Rails 7.0 to 7.2 our code started to break because of an incompatibility between Rails 7.2 and activerecord-jdbc-adapter. I investigated the problem with the help of an AI tool and made this PR with its help.

It would be nice if I could get this fixed in a activerecord-jdbc-adapter 72.x version.

Happy to modify this PR as required by the maintainer. TIA.