[CALCITE-4556] CalciteMetaImpl#createEmptyResultSet override of (Avatica) MetaImpl#createEmptyResultSet should not pass a class instance to CursorFactory#deduce

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.26.0
• Fix Version/s: 1.27.0
• Component/s: jdbc-driver
• Labels: pull-request-available
• Assignee: Alessandro Solimando
• Reporter: Alessandro Solimando
• Created: 28/Mar/21 10:26
• Updated: 03/Jun/21 22:31
• Resolved: 29/Mar/21 07:12

Description

In Avatica 1.18.0, `CursorFactory#deduce(List<ColumnMetaData> columns, Class resultClazz)` introduces a validation step requiring the names appearing in the column metadata to match fields of `resultClazz`, whenever the class is not null.

`CalciteMetaImpl#createEmptyResultSet` overrides `MetaImpl#createEmptyResultSet` (class from Avatica), only to pass a value non null value to the `resultClazz` argument.

Column metadata column names for Calcite internal metadata classes (e.g., `MetaColumn`, `MetaCatalog`, `MetaSchema`, etc.) are built using `MetaImpl#fieldMetadata` (transforming the name from camel case into upper-snake case), violating the new contract of `deduce`.

This is not problematic, because `deduce` is only used to create an empty result set, we are only interested in preserving the sought column names, which is already the case for `MetaImpl#createEmptyResultSet`.

`CalciteMetaImpl#createEmptyResultSet`, if adapted to match the changes coming from Avatica 1.18.0 would become identical to the `MetaImpl#createEmptyResultSet` it overrides, and it should therefore be removed.

Issue Links

• relates to: CALCITE-4503 Order of fields in records should follow that of the SQL types
• links to: GitHub Pull Request #2384