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Mike Bayer
3b4bbbb2a3
Improved the :func:`_sql.tuple_` construct such that it behaves predictably when used in a columns-clause context. The SQL tuple is not supported as a "SELECT" columns clause element on most backends; on those that do (PostgreSQL, not surprisingly), the Python DBAPI does not have a "nested type" concept so there are still challenges in fetching rows for such an object. Use of :func:`_sql.tuple_` in a :func:`_sql.select` or :class:`_orm.Query` will now raise a :class:`_exc.CompileError` at the point at which the :func:`_sql.tuple_` object is seen as presenting itself for fetching rows (i.e., if the tuple is in the columns clause of a subquery, no error is raised). For ORM use,the :class:`_orm.Bundle` object is an explicit directive that a series of columns should be returned as a sub-tuple per row and is suggested by the error message. Additionally ,the tuple will now render with parenthesis in all contexts. Previously, the parenthesization would not render in a columns context leading to non-defined behavior. As part of this change, Tuple receives a dedicated datatype which appears to allow us the very desirable change of removing the bindparam._expanding_in_types attribute as well as ClauseList._tuple_values (which might already have not been needed due to #4645). Fixes: #5127 Change-Id: Iecafa0e0aac2f1f37ec8d0e1631d562611c90200