[Sqlalchemy-tickets] Issue #4226: SQLite and JSON: AttributeError (zzzeek/sqlalchemy)

[Sebastian R. <iss...@bi...>]

New issue 4226: SQLite and JSON: AttributeError
https://bitbucket.org/zzzeek/sqlalchemy/issues/4226/sqlite-and-json-attributeerror

Sebastian Rittau:

Please consider the following code:

```
#!python

from sqlalchemy import create_engine, Column
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker
from sqlalchemy.types import Integer, JSON


DeclarativeBase = declarative_base()


class Foo(DeclarativeBase):

    __tablename__ = "foo"

    id = Column(Integer, primary_key=True)
    json = Column(JSON)


engine = create_engine("sqlite:///")
engine.execute("CREATE TABLE foo(id INTEGER PRIMARY KEY, json JSON)")
engine.execute("INSERT INTO foo(id, json) VALUES(123, '\"bar\"')")
session = sessionmaker(bind=engine)()
session.query(Foo).first()
```

Running this with SQLAlchemy 1.2.5 and Python 3.6.5rc1, I get the following traceback:

```
Traceback (most recent call last):
  File "/home/srittau/.virtualenvs/zc-api-3.6/lib/python3.6/site-packages/sqlalchemy/sql/type_api.py", line 471, in _cached_result_processor
    return dialect._type_memos[self][coltype]
  File "/usr/lib/python3.6/weakref.py", line 394, in __getitem__
    return self.data[ref(key)]
KeyError: <weakref at 0x7f7466d6f688; to 'JSON' at 0x7f746a797588>

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/srittau/.PyCharm2017.3/config/scratches/scratch_13.py", line 22, in <module>
    session.query(Foo).first()
  File "/home/srittau/.virtualenvs/zc-api-3.6/lib/python3.6/site-packages/sqlalchemy/orm/query.py", line 2789, in first
    ret = list(self[0:1])
  File "/home/srittau/.virtualenvs/zc-api-3.6/lib/python3.6/site-packages/sqlalchemy/orm/query.py", line 2581, in __getitem__
    return list(res)
  File "/home/srittau/.virtualenvs/zc-api-3.6/lib/python3.6/site-packages/sqlalchemy/orm/query.py", line 2889, in __iter__
    return self._execute_and_instances(context)
  File "/home/srittau/.virtualenvs/zc-api-3.6/lib/python3.6/site-packages/sqlalchemy/orm/query.py", line 2912, in _execute_and_instances
    result = conn.execute(querycontext.statement, self._params)
  File "/home/srittau/.virtualenvs/zc-api-3.6/lib/python3.6/site-packages/sqlalchemy/engine/base.py", line 948, in execute
    return meth(self, multiparams, params)
  File "/home/srittau/.virtualenvs/zc-api-3.6/lib/python3.6/site-packages/sqlalchemy/sql/elements.py", line 269, in _execute_on_connection
    return connection._execute_clauseelement(self, multiparams, params)
  File "/home/srittau/.virtualenvs/zc-api-3.6/lib/python3.6/site-packages/sqlalchemy/engine/base.py", line 1060, in _execute_clauseelement
    compiled_sql, distilled_params
  File "/home/srittau/.virtualenvs/zc-api-3.6/lib/python3.6/site-packages/sqlalchemy/engine/base.py", line 1215, in _execute_context
    result = context.get_result_proxy()
  File "/home/srittau/.virtualenvs/zc-api-3.6/lib/python3.6/site-packages/sqlalchemy/engine/default.py", line 1008, in get_result_proxy
    return result.ResultProxy(self)
  File "/home/srittau/.virtualenvs/zc-api-3.6/lib/python3.6/site-packages/sqlalchemy/engine/result.py", line 649, in __init__
    self._init_metadata()
  File "/home/srittau/.virtualenvs/zc-api-3.6/lib/python3.6/site-packages/sqlalchemy/engine/result.py", line 678, in _init_metadata
    self._metadata = ResultMetaData(self, cursor_description)
  File "/home/srittau/.virtualenvs/zc-api-3.6/lib/python3.6/site-packages/sqlalchemy/engine/result.py", line 215, in __init__
    num_ctx_cols, cols_are_ordered, textual_ordered)
  File "/home/srittau/.virtualenvs/zc-api-3.6/lib/python3.6/site-packages/sqlalchemy/engine/result.py", line 379, in _merge_cursor_description
    in enumerate(result_columns)
  File "/home/srittau/.virtualenvs/zc-api-3.6/lib/python3.6/site-packages/sqlalchemy/engine/result.py", line 378, in <listcomp>
    ) for idx, (key, name, obj, type_)
  File "/home/srittau/.virtualenvs/zc-api-3.6/lib/python3.6/site-packages/sqlalchemy/engine/default.py", line 971, in get_result_processor
    return type_._cached_result_processor(self.dialect, coltype)
  File "/home/srittau/.virtualenvs/zc-api-3.6/lib/python3.6/site-packages/sqlalchemy/sql/type_api.py", line 477, in _cached_result_processor
    d[coltype] = rp = d['impl'].result_processor(dialect, coltype)
  File "/home/srittau/.virtualenvs/zc-api-3.6/lib/python3.6/site-packages/sqlalchemy/sql/sqltypes.py", line 2148, in result_processor
    json_deserializer = dialect._json_deserializer or json.loads
AttributeError: 'SQLiteDialect_pysqlite' object has no attribute '_json_deserializer'
```

Line 2148 of `sqlalchemy/sql/sqltypes.py` reads:

```
        json_deserializer = dialect._json_deserializer or json.loads
```

I suspect this is supposed to read

```
        json_deserializer = dialect._json_deserializer if hasattr(dialect, "_json_deserializer") else json.loads
```

to support dialects without native JSON support.