[Sqlalchemy-tickets] Issue #3832: _set_table not called in 1.1 on custom type based on TypeDecorator & SchemaType (zzzeek/sqlalchemy)

[Adrian <iss...@bi...>]

New issue 3832: _set_table not called in 1.1 on custom type based on TypeDecorator & SchemaType
https://bitbucket.org/zzzeek/sqlalchemy/issues/3832/_set_table-not-called-in-11-on-custom-type

Adrian:

We are using a custom class handling int-based enums (since 1.0 didn't have python-native enum support) with an autogenerated CHECK constraint. In 1.1 this constraint is not added anymore.

In the [changelog entry](http://docs.sqlalchemy.org/en/rel_1_1/changelog/migration_11.html#typedecorator-now-works-with-enum-boolean-schema-types-automatically) regarding TypeDecorator I couldn't see any reason why _set_table would not be called anymore.

```python
from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.sql.sqltypes import SchemaType
from enum import Enum


Base = declarative_base()


class PyIntEnum(TypeDecorator, SchemaType):
    impl = SmallInteger

    def __init__(self, enum=None, exclude_values=None):
        self.enum = enum
        self.exclude_values = set(exclude_values or ())
        TypeDecorator.__init__(self)
        SchemaType.__init__(self)

    def process_bind_param(self, value, dialect):
        return int(value) if value is not None else None

    def process_result_value(self, value, dialect):
        pass  # not relevant for DDL

    def _set_table(self, column, table):
        e = CheckConstraint(type_coerce(column, self).in_(x.value for x in self.enum if x not in self.exclude_values),
                            'valid_enum_{}'.format(column.name))
        e.info['alembic_dont_render'] = True
        assert e.table is table


class MyEnum(int, Enum):
    a = 1
    b = 2
    c = 3


class Foo(Base):
    __tablename__ = 'foo'
    id = Column(Integer, primary_key=True)
    enum = Column(PyIntEnum(MyEnum))


e = create_engine('postgresql:///test', echo=True)
Base.metadata.drop_all(e)
Base.metadata.create_all(e)
```

SQL emitted in 1.1:

```sql
CREATE TABLE foo (
        id SERIAL NOT NULL,
        enum SMALLINT,
        PRIMARY KEY (id)
)
```

SQL emitted in 1.0
```sql
CREATE TABLE foo (
        id SERIAL NOT NULL,
        enum SMALLINT,
        PRIMARY KEY (id),
        CONSTRAINT valid_enum_enum CHECK (enum IN (1, 2, 3))
)
```