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cursor.description's type_code is always None, even though col_types is already available internally

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Bewertung

Schwierigkeit
3/5
Geschätzter Aufwand
1-2 Tage
Anfängerfreundlichkeit
72/100
Issue-Typ
Bug
Klarheit
Klar beschrieben
Aktivitätsstatus
Aktiv
Tech-Stack
python
Bereich
database, databases

Rechercherichtung

Read src/crate/client/cursor.py's Cursor.description property and the type definitions and _resolve() helper in src/crate/client/converter.py. Check how col_types is populated and how existing cursor tests cover description; add coverage for the type_code value when column types are available. Done means the public description exposes each column's type code without requiring a configured Converter.

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Beschreibung

Summary

`Cursor.description` (PEP 249) always returns `None` for every field after the column name, including `type_code`:

https://github.com/crate/crate-python/blob/main/src/crate/client/cursor.py

```python
@property
def description(self):
if self._closed:
return None

description = []
for col in self._result["cols"]:
    description.append((col, None, None, None, None, None, None))
return tuple(description)

```

This isn't because the driver doesn't have the type information. `self._result["col_types"]` is already populated from the same HTTP response (CrateDB's HTTP SQL interface column types) and is already used internally, e.g. in `Cursor._convert_rows()`:

```python
def _convert_rows(self):
if not ("col_types" in self._result and self._result["col_types"]):
raise ValueError(...)
types = self.result["col_types"]
converters = [self.converter.get(type) for type in types]
...
```

and `converter.py` already has a complete, documented mapping from these wire type codes to a `DataType` enum (`TIMESTAMP_WITH_TZ = 11`, `TIMESTAMP_WITHOUT_TZ = 15`, etc.) — so the information isn't missing, it's just not propagated into the public `description` property.

Why this matters

`type_code` is part of the standard DB-API 2.0 `description` contract (PEP 249). A consumer that only has a `Cursor` object (e.g. a driver-agnostic tool built against SQLAlchemy's cursor/dialect layer, or any generic DB-API client) has no supported way to find out a column's CrateDB type without either enabling a `Converter` (which changes value representation, not just exposing the type) or reaching into the private `cursor._result["col_types"]` attribute directly, which isn't part of the public API and could change without notice.

We actually hit this downstream in Apache Superset: `CrateEngineSpec.fetch_data()` has to read `cursor._result.get("col_types", [])` directly to tell timestamp columns apart from plain numeric ones, specifically because `cursor.description`'s `type_code` is always `None`:
https://github.com/apache/superset/blob/master/superset/db_engine_specs/crate.py#L98-L123

Suggested fix

In `Cursor.description`, populate the `type_code` slot (index 1 of the 7-tuple) from `self._result["col_types"]` (resolved through the existing `DataType` enum / `_resolve()` helper in `converter.py`) instead of hardcoding `None`, when `col_types` is available. This would bring `description` in line with the PEP 249 contract without needing a `Converter` to be configured, and let consumers stop reaching into `cursor._result` directly.

Environment
  • crate-python: current `main` (same code present going back through recent tags)
  • Verified by reading `src/crate/client/cursor.py` and `src/crate/client/converter.py` directly, cross-checked against the CrateDB HTTP SQL docs' column-types table.
Vorherrschende Sprache
Python
Sterne
85
Forks
35
Ø Merge
2 T. 13 Std.
Gemergte PRs (30 T.)
2

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