Fix: MSSQL add N char

[ansutung]

Summary by CodeRabbit

• New Features

  • Added connectors for Redshift, Postgres, SQL Server, and Canner.
  • DuckDB can attach additional databases and list/attach files from S3 or local storage.
  • Query results now return as Apache Arrow tables for improved performance and compatibility.
  • Automatic handling of Decimal and UUID types for consistent outputs.

• Bug Fixes

  • Unified, clearer error messages across connectors; safer dry-run behavior.
  • More robust connection closing to prevent crashes or double-closing.
  • MSSQL correctly handles Unicode string literals.
  • Preserved timeout semantics while improving invalid SQL detection.

[coderabbitai[bot]]

Walkthrough

Adds multiple connectors (Redshift, Postgres, MSSQL, Canner), changes query return type to PyArrow tables, introduces unified error handling, implements close semantics, enhances DuckDB behaviors, and adds utilities for UUID/Decimal post-processing and PostgreSQL type-name retrieval in ibis-server/app/model/connector.py.

Changes

Cohort / File(s)	Summary of Changes
Connector additions ibis-server/app/model/connector.py	Introduces RedshiftConnector, PostgresConnector, MSSqlConnector, and CannerConnector with query/dry_run implementations and close methods.
API return type updates ibis-server/app/model/connector.py	Updates Connector.query and SimpleConnector.query to return pa.Table instead of pandas DataFrame.
Unified error handling ibis-server/app/model/connector.py	Wraps backend exceptions into WrenError with ErrorCode/ErrorPhase; adjusts mappings (e.g., timeouts vs INVALID_SQL) across query and dry_run.
PyArrow post-processing ibis-server/app/model/connector.py	Adds _handle_pyarrow_unsupported_type, _cast_uuid_columns, _round_decimal_columns in SimpleConnector to cast UUIDs to string and round Decimals to a fixed scale.
Close semantics and safety ibis-server/app/model/connector.py	Adds close() methods to multiple connectors with safeguards to avoid double-closing and segfaults.
DuckDB enhancements ibis-server/app/model/connector.py	Enables attaching additional DuckDB databases, listing/attaching files via S3/Local FS interfaces, and improves dry_run/close safety.
PostgreSQL type helper ibis-server/app/model/connector.py	Adds _get_pg_type_names(connection) to retrieve PostgreSQL OID-to-type-name mappings.

Sequence Diagram(s)

sequenceDiagram
  autonumber
  actor Client
  participant Connector as SimpleConnector
  participant Ibis as Ibis Backend
  participant Arrow as PyArrow
  Note over Connector,Ibis: Query execution with PyArrow result
  Client->>Connector: query(sql, limit)
  Connector->>Ibis: compile/execute(sql, limit)
  Ibis-->>Connector: result (backend table)
  rect rgb(245,245,255)
    Note right of Connector: Post-process unsupported types
    Connector->>Connector: _handle_pyarrow_unsupported_type()
    Connector->>Connector: _cast_uuid_columns()
    Connector->>Connector: _round_decimal_columns(scale=9)
  end
  Connector->>Arrow: to_arrow()
  Arrow-->>Connector: pa.Table
  Connector-->>Client: pa.Table

sequenceDiagram
  autonumber
  actor Client
  participant Conn as AnyConnector
  participant Backend as Driver/DB
  participant Err as WrenError
  Note over Conn,Backend: Unified error handling for query/dry_run
  Client->>Conn: dry_run(sql) / query(sql)
  Conn->>Backend: execute / explain
  alt Success
    Backend-->>Conn: OK / result
    Conn-->>Client: Response
  else Backend raises (Trino/ClickHouse/psycopg/...)
    Backend-->>Conn: Exception
    rect rgb(255,245,245)
      Note right of Conn: Map to ErrorCode + ErrorPhase
      Conn->>Err: wrap(exception)
    end
    Err-->>Client: WrenError
  end

sequenceDiagram
  autonumber
  actor Client
  participant RS as RedshiftConnector
  participant Psy as psycopg Cursor
  participant Arrow as PyArrow
  Note over RS,Psy: Redshift autocommit + Python-level cursor
  Client->>RS: query(sql, limit)
  RS->>Psy: execute(sql)
  Psy-->>RS: rows / cursor data
  RS->>Arrow: to_arrow()
  Arrow-->>RS: pa.Table
  RS-->>Client: pa.Table
  Client->>RS: close()
  RS-->>Client: closed

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~60 minutes

Possibly related PRs

• Canner/wren-engine#1247 — Both touch DuckDBConnector: attach/list helpers and query return/signature changes align with this PR.
• Canner/wren-engine#1207 — Shares _get_pg_type_names helper introduction and cursor/close handling in the same module.

Suggested labels

ibis, python

Suggested reviewers

• douenergy
• goldmedal

Poem

(\/) ( ••)✧ hop! New bridges built to data streams, UUIDs tamed, and Decimal gleams. Errors corralled, one burrowed voice— Arrow feathers our swift choice. Close the tunnel—quiet, poised.

Pre-merge checks and finishing touches

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 17.50% which is insufficient. The required threshold is 80.00%.	You can run `@coderabbitai generate docstrings` to improve docstring coverage.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit's high-level summary is enabled.
Title Check	✅ Passed	The title mentions adding an N prefix for MSSQL Unicode literals, which corresponds to a valid subset of the changes. However, it does not reflect the primary objective of this pull request, which is the broad expansion of multi-backend support—including new Redshift, Postgres, MSSQL, and Canner connectors—along with enhanced PyArrow handling, unified error wrapping, and robust closing logic.

✨ Finishing touches

• [ ] 📝 Generate Docstrings

🧪 Generate unit tests

• [ ] Create PR with unit tests
• [ ] Post copyable unit tests in a comment

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[goldmedal]

@ansutung, could you rebase on the latest main and add the description for what you want to propose?

[goldmedal]

It may be a duplicate of https://github.com/Canner/wren-engine/pull/1338