[Sqlalchemy-tickets] Issue #4372: deferred Column attribute in CheckConstraint (zzzeek/sqlalchemy)

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New issue 4372: deferred Column attribute in CheckConstraint
https://bitbucket.org/zzzeek/sqlalchemy/issues/4372/deferred-column-attribute-in

Dmytro Starosud:

This is using SQLAlchemy==1.2.14.

```
#!python

from sqlalchemy import CheckConstraint, Column, DateTime, Integer, create_engine, func
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import deferred
from sqlalchemy.pool import NullPool

engine = create_engine('postgresql://***', poolclass=NullPool)
connection = engine.connect()
connection.begin_nested()

Base = declarative_base()

class MyEntity(Base):
    __tablename__ = 'my_entity'

    id = Column(Integer, primary_key=True)

    _internal_modified_at = deferred(Column(
        DateTime(timezone=True), nullable=False, index=True,
        server_default=func.now(), onupdate=func.now()))

    __table_args__ = (
        CheckConstraint(
            _internal_modified_at == func.now(),
            'my_entity_is_modified_now'),
    )

Base.metadata.create_all(connection)
```

Last line produces exception:

```
root@0d982765aeb0:/service# python main.py
/usr/local/lib/python3.5/site-packages/psycopg2/__init__.py:144: UserWarning: The psycopg2 wheel package will be renamed from release 2.8; in order to keep installing from binary please use "pip install psycopg2-binary" instead. For details see: <http://initd.org/psycopg/docs/install.html#binary-install-from-pypi>.
  """)
Traceback (most recent call last):
  File "main.py", line 29, in <module>
    Base.metadata.create_all(connection)
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/sql/schema.py", line 4005, in create_all
    tables=tables)
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/engine/base.py", line 1549, in _run_visitor
    **kwargs).traverse_single(element)
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/sql/visitors.py", line 121, in traverse_single
    return meth(obj, **kw)
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/sql/ddl.py", line 757, in visit_metadata
    _is_metadata_operation=True)
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/sql/visitors.py", line 121, in traverse_single
    return meth(obj, **kw)
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/sql/ddl.py", line 791, in visit_table
    include_foreign_key_constraints=include_foreign_key_constraints
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/engine/base.py", line 948, in execute
    return meth(self, multiparams, params)
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/sql/ddl.py", line 68, in _execute_on_connection
    return connection._execute_ddl(self, multiparams, params)
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/engine/base.py", line 1003, in _execute_ddl
    if not self.schema_for_object.is_default else None)
  File "<string>", line 1, in <lambda>
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/sql/elements.py", line 442, in compile
    return self._compiler(dialect, bind=bind, **kw)
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/sql/ddl.py", line 26, in _compiler
    return dialect.ddl_compiler(dialect, self, **kw)
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/sql/compiler.py", line 219, in __init__
    self.string = self.process(self.statement, **compile_kwargs)
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/sql/compiler.py", line 245, in process
    return obj._compiler_dispatch(self, **kwargs)
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/sql/visitors.py", line 81, in _compiler_dispatch
    return meth(self, **kw)
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/sql/compiler.py", line 2502, in visit_create_table
    create.include_foreign_key_constraints)
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/sql/compiler.py", line 2549, in create_table_constraints
    for constraint in constraints
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/sql/compiler.py", line 2547, in <genexpr>
    p for p in
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/sql/compiler.py", line 2555, in <genexpr>
    not getattr(constraint, 'use_alter', False)
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/sql/compiler.py", line 245, in process
    return obj._compiler_dispatch(self, **kwargs)
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/sql/visitors.py", line 93, in _compiler_dispatch
    return meth(self, **kw)
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/sql/compiler.py", line 2732, in visit_check_constraint
    literal_binds=True)
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/sql/compiler.py", line 245, in process
    return obj._compiler_dispatch(self, **kwargs)
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/sql/visitors.py", line 81, in _compiler_dispatch
    return meth(self, **kw)
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/sql/compiler.py", line 1078, in visit_binary
    return self._generate_generic_binary(binary, opstring, **kw)
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/sql/compiler.py", line 1111, in _generate_generic_binary
    self, eager_grouping=eager_grouping, **kw)
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/sql/visitors.py", line 81, in _compiler_dispatch
    return meth(self, **kw)
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/sql/compiler.py", line 1242, in visit_bindparam
    bindparam, within_columns_clause=True, **kwargs)
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/sql/compiler.py", line 1275, in render_literal_bindparam
    return self.render_literal_value(value, bindparam.type)
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/dialects/postgresql/base.py", line 1490, in render_literal_value
    value = super(PGCompiler, self).render_literal_value(value, type_)
  File "/usr/local/lib/python3.5/site-packages/sqlalchemy/sql/compiler.py", line 1293, in render_literal_value
    "Don't know how to literal-quote value %r" % value)
NotImplementedError: Don't know how to literal-quote value <ColumnProperty at 0x7f12c9ff8dd8; _internal_modified_at>
```