:released: November 11, 2019

 .. change::
     :tags: bug, mssql
     :tickets: 4973

     Fixed issue in MSSQL dialect where an expression-based OFFSET value in a
     SELECT would be rejected, even though the dialect can render this
     expression inside of a ROW NUMBER-oriented LIMIT/OFFSET construct.


 .. change::
     :tags: orm, usecase
     :tickets: 4934

     Added accessor :meth:`.Query.is_single_entity` to :class:`.Query`, which
     will indicate if the results returned by this :class:`.Query` will be a
     list of ORM entities, or a tuple of entities or column expressions.
     SQLAlchemy hopes to improve upon the behavior of single entity / tuples in
     future releases such that the behavior would be explicit up front, however
     this attribute should be helpful with the current behavior.  Pull request
     courtesy Patrick Hayes.

 .. change::
     :tags: bug, mysql
     :tickets: 4945

     Added "Connection was killed" message interpreted from the base
     pymysql.Error class in order to detect closed connection, based on reports
     that this message is arriving via a pymysql.InternalError() object which
     indicates pymysql is not handling it correctly.

 .. change::
     :tags: bug, orm
     :tickets: 4954

     The :paramref:`.relationship.omit_join` flag was not intended to be
     manually set to True, and will now emit a warning when this occurs.  The
     omit_join optimization is detected automatically, and the ``omit_join``
     flag was only intended to disable the optimization in the hypothetical case
     that the optimization may have interfered with correct results, which has
     not been observed with the modern version of this feature.   Setting the
     flag to True when it is not automatically detected may cause the selectin
     load feature to not work correctly when a non-default primary join
     condition is in use.


 .. change::
     :tags: bug, orm
     :tickets: 4915

     A warning is emitted if a primary key value is passed to :meth:`.Query.get`
     that consists of None for all primary key column positions.   Previously,
     passing a single None outside of a tuple would raise a ``TypeError`` and
     passing a composite None (tuple of None values) would silently pass
     through.   The fix now coerces the single None into a tuple where it is
     handled consistently with the other None conditions.  Thanks to Lev
     Izraelit for the help with this.


 .. change::
     :tags: bug, orm
     :tickets: 4947

     The :class:`.BakedQuery` will not cache a query that was modified by a
     :meth:`.QueryEvents.before_compile` event, so that compilation hooks that
     may be applying ad-hoc modifications to queries will take effect on each
     run.  In particular this is helpful for events that modify queries used in
     lazy loading as well as eager loading such as "select in" loading.  In
     order to re-enable caching for a query modified by this event, a new
     flag ``bake_ok`` is added; see :ref:`baked_with_before_compile` for
     details.

     A longer term plan to provide a new form of SQL caching should solve this
     kind of issue more comprehensively.

 .. change::
     :tags: bug, tests
     :tickets: 4920

     Fixed test failures which would occur with newer SQLite as of version 3.30
     or greater, due to their addition of nulls ordering syntax as well as new
     restrictions on aggregate functions.  Pull request courtesy Nils Philippsen.



 .. change::
     :tags: bug, installation, windows
     :tickets: 4967

     Added a workaround for a setuptools-related failure that has been observed
     as occurring on Windows installations, where setuptools is not correctly
     reporting a build error when the MSVC build dependencies are not installed
     and therefore not allowing graceful degradation into non C extensions
     builds.

 .. change::
     :tags: bug, sql, py3k
     :tickets: 4931

     Changed the ``repr()`` of the :class:`.quoted_name` construct to use
     regular string repr() under Python 3, rather than running it through
     "backslashreplace" escaping, which can be misleading.

 .. change::
     :tags: bug, oracle, firebird
     :tickets: 4931

     Modified the approach of "name normalization" for the Oracle and Firebird
     dialects, which converts from the UPPERCASE-as-case-insensitive convention
     of these dialects into lowercase-as-case-insensitive for SQLAlchemy, to not
     automatically apply the :class:`.quoted_name` construct to a name that
     matches itself under upper or lower case conversion, as is the case for
     many non-european characters.   All names used within metadata structures
     are converted to :class:`.quoted_name` objects in any case; the change
     here would only affect the output of some inspection functions.

 .. change::
     :tags: bug, schema
     :tickets: 4911

     Fixed bug where a table that would have a column label overlap with a plain
     column name, such as "foo.id AS foo_id" vs. "foo.foo_id", would prematurely
     generate the ``._label`` attribute for a column before this overlap could
     be detected due to the use of the ``index=True`` or ``unique=True`` flag on
     the column in conjunction with the default naming convention of
     ``"column_0_label"``.  This would then lead to failures when ``._label``
     were used later to generate a bound parameter name, in particular those
     used by the ORM when generating the WHERE clause for an UPDATE statement.
     The issue has been fixed by using an alternate ``._label`` accessor for DDL
     generation that does not affect the state of the :class:`.Column`.   The
     accessor also bypasses the key-deduplication step as it is not necessary
     for DDL, the naming is now consistently ``"<tablename>_<columnname>"``
     without any subsequent numeric symbols when used in DDL.



 .. change::
     :tags: bug, engine
     :tickets: 4902

     Fixed bug where parameter repr as used in logging and error reporting needs
     additional context in order to distinguish between a list of parameters for
     a single statement and a list of parameter lists, as the "list of lists"
     structure could also indicate a single parameter list where the first
     parameter itself is a list, such as for an array parameter.   The
     engine/connection now passes in an additional boolean indicating how the
     parameters should be considered.  The only SQLAlchemy backend that expects
     arrays as parameters is that of  psycopg2 which uses pyformat parameters,
     so this issue has not been too apparent, however as other drivers that use
     positional gain more features it is important that this be supported. It
     also eliminates the need for the parameter repr function to guess based on
     the parameter structure passed.

 .. change::
     :tags: usecase, schema
     :tickets: 4894

     Added DDL support for "computed columns"; these are DDL column
     specifications for columns that have a server-computed value, either upon
     SELECT (known as "virtual") or at the point of which they are INSERTed or
     UPDATEd (known as "stored").  Support is established for Postgresql, MySQL,
     Oracle SQL Server and Firebird. Thanks to Federico Caselli for lots of work
     on this one.

     .. seealso::

         :ref:`computed_ddl`


 .. change::
     :tags: bug, engine, postgresql
     :tickets: 4955

     Fixed bug in :class:`.Inspector` where the cache key generation did not
     take into account arguments passed in the form of tuples, such as the tuple
     of view name styles to return for the PostgreSQL dialect. This would lead
     the inspector to cache too generally for a more specific set of criteria.
     The logic has been adjusted to include every keyword element in the cache,
     as every argument is expected to be appropriate for a cache else the
     caching decorator should be bypassed by the dialect.


 .. change::
     :tags: bug, mssql
     :tickets: 4923

     Fixed an issue in the :meth:`.Engine.table_names` method where it would
     feed the dialect's default schema name back into the dialect level table
     function, which in the case of SQL Server would interpret it as a
     dot-tokenized schema name as viewed by the mssql dialect, which would
     cause the method to fail in the case where the database username actually
     had a dot inside of it.  In 1.3, this method is still used by the
     :meth:`.MetaData.reflect` function so is a prominent codepath. In 1.4,
     which is the current master development branch, this issue doesn't exist,
     both because :meth:`.MetaData.reflect` isn't using this method nor does the
     method pass the default schema name explicitly.  The fix nonetheless
     guards against the default server name value returned by the dialect from
     being interpreted as dot-tokenized name under any circumstances by
     wrapping it in quoted_name().

 .. change::
     :tags: bug, orm
     :tickets: 4974

     Fixed ORM bug where a "secondary" table that referred to a selectable which
     in some way would refer to the local primary table would apply aliasing to
     both sides of the join condition when a relationship-related join, either
     via :meth:`.Query.join` or by :func:`.joinedload`, were generated.  The
     "local" side is now excluded.

 .. change::
     :tags: usecase, sql
     :tickets: 4276

     Added new accessors to expressions of type :class:`.JSON` to allow for
     specific datatype access and comparison, covering strings, integers,
     numeric, boolean elements.   This revises the documented approach of
     CASTing to string when comparing values, instead adding specific
     functionality into the PostgreSQL, SQlite, MySQL dialects to reliably
     deliver these basic types in all cases.

     .. seealso::

         :class:`.JSON`

         :meth:`.JSON.Comparator.as_string`

         :meth:`.JSON.Comparator.as_boolean`

         :meth:`.JSON.Comparator.as_float`

         :meth:`.JSON.Comparator.as_integer`

 .. change::
     :tags: usecase, oracle
     :tickets: 4799

     Added dialect-level flag ``encoding_errors`` to the cx_Oracle dialect,
     which can be specified as part of :func:`.create_engine`.   This is passed
     to SQLAlchemy's unicode decoding converter under Python 2, and to
     cx_Oracle's ``cursor.var()`` object as the ``encodingErrors`` parameter
     under Python 3, for the very unusual case that broken encodings are present
     in the target database which cannot be fetched unless error handling is
     relaxed.  The value is ultimately one of the Python "encoding errors"
     parameters passed to ``decode()``.

 .. change::
     :tags: usecase, sql
     :tickets: 4933

     The :func:`.text` construct now supports "unique" bound parameters, which
     will dynamically uniquify themselves on compilation thus allowing multiple
     :func:`.text` constructs with the same bound parameter names to be combined
     together.


 .. change::
     :tags: bug, oracle
     :tickets: 4913

     The :class:`.sqltypes.NCHAR` datatype will now bind to the
     ``cx_Oracle.FIXED_NCHAR`` DBAPI data bindings when used in a bound
     parameter, which supplies proper comparison behavior against a
     variable-length string.  Previously, the :class:`.sqltypes.NCHAR` datatype
     would bind to ``cx_oracle.NCHAR`` which is not fixed length; the
     :class:`.sqltypes.CHAR` datatype already binds to ``cx_Oracle.FIXED_CHAR``
     so it is now consistent that :class:`.sqltypes.NCHAR` binds to
     ``cx_Oracle.FIXED_NCHAR``.



 .. change::
     :tags: bug, firebird
     :tickets: 4903

     Added additional "disconnect" message "Error writing data to the
     connection" to Firebird disconnection detection.  Pull request courtesy
     lukens.

.. changelog::