mcp-hydrolix

Instructions

Implementation Reference

• mcp_hydrolix/mcp_server.py:147-177 (handler)

  The primary handler for the 'list_tables' tool. Decorated with @mcp.tool() for registration in FastMCP. Executes queries against system.tables and system.columns to fetch comprehensive table information including metadata and column details.

  @mcp.tool()
  def list_tables(database: str, like: Optional[str] = None, not_like: Optional[str] = None):
      """List available Hydrolix tables in a database, including schema, comment,
      row count, and column count."""
      logger.info(f"Listing tables in database '{database}'")
      client = create_hydrolix_client(get_request_credential())
      query = f"SELECT database, name, engine, create_table_query, dependencies_database, dependencies_table, engine_full, sorting_key, primary_key, total_rows, total_bytes, total_bytes_uncompressed, parts, active_parts, total_marks, comment FROM system.tables WHERE database = {format_query_value(database)}"
      if like:
          query += f" AND name LIKE {format_query_value(like)}"
  
      if not_like:
          query += f" AND name NOT LIKE {format_query_value(not_like)}"
  
      result = client.query(query)
  
      # Deserialize result as Table dataclass instances
      tables = result_to_table(result.column_names, result.result_rows)
  
      for table in tables:
          column_data_query = f"SELECT database, table, name, type AS column_type, default_kind, default_expression, comment FROM system.columns WHERE database = {format_query_value(database)} AND table = {format_query_value(table.name)}"
          column_data_query_result = client.query(column_data_query)
          table.columns = [
              c
              for c in result_to_column(
                  column_data_query_result.column_names,
                  column_data_query_result.result_rows,
              )
          ]
  
      logger.info(f"Found {len(tables)} tables")
      return [asdict(table) for table in tables]

• mcp_hydrolix/mcp_server.py:41-58 (schema)

  Dataclass defining the structure for table metadata returned by list_tables, used for output schema.

  class Table:
      database: str
      name: str
      engine: str
      create_table_query: str
      dependencies_database: str
      dependencies_table: str
      engine_full: str
      sorting_key: str
      primary_key: str
      total_rows: int
      total_bytes: int
      total_bytes_uncompressed: int
      parts: int
      active_parts: int
      total_marks: int
      comment: Optional[str] = None
      columns: List[Column] = field(default_factory=list)

• mcp_hydrolix/mcp_server.py:29-37 (schema)

  Dataclass defining the structure for column metadata nested within Table objects.

  @dataclass
  class Column:
      database: str
      table: str
      name: str
      column_type: str
      default_kind: Optional[str]
      default_expression: Optional[str]
      comment: Optional[str]

• mcp_hydrolix/mcp_server.py:108-110 (helper)

  Helper function to convert query results into List[Table] instances.

  def result_to_table(query_columns, result) -> List[Table]:
      return [Table(**dict(zip(query_columns, row))) for row in result]

• mcp_hydrolix/mcp_server.py:112-114 (helper)

  Helper function to convert query results into List[Column] instances.

  def result_to_column(query_columns, result) -> List[Column]:
      return [Column(**dict(zip(query_columns, row))) for row in result]