Enum + Clickhouse 1.4 = crash

[anatoly-scherbakov]

Describe the bug

In certain circumstances, when querying a table with an Enum column an error is thrown:

File "/usr/local/lib/python3.8/site-packages/sqlalchemy/engine/result.py", line 393, in _raw_all_rows
return [make_row(row) for row in rows]
File "/usr/local/lib/python3.8/site-packages/sqlalchemy/engine/result.py", line 393, in
return [make_row(row) for row in rows]
File "/usr/local/lib/python3.8/site-packages/sqlalchemy/sql/sqltypes.py", line 1768, in process
value = parent_processor(value)
TypeError: expected bytes, str found

To Reproduce

• Create a table with a clickhouse_sqlalchemy.types.Enum field
• Fill it with data
• SELECT some data from it via SQLAlchemy

Expected behavior

The same code worked correctly on SQLAlchemy 1.3 and it was expected for it to continue that way.

How to fix

Method 1:

    engine = create_engine(...)
    engine.dialect.returns_unicode_strings = String.RETURNS_UNICODE

After this change, String.result_processor method will invoke processors.to_conditional_unicode_processor_factory() instead of processors.to_unicode_processor_factory() to obtain the result converting function.

Method 2: in addition to the above, assign:

    engine.dialect.convert_unicode = False

This will mean that no conversion at all will happen because SQLAlchemy will expect to receive proper Unicode strings from the driver. This should provide a bit higher performance.

Versions

Python: 3.8.12.
Libraries:

SQLAlchemy = "^1.4"
clickhouse-sqlalchemy = "^0.2.1"