Class ColumnCollection

lib/sqlalchemy/sql/base.py:1510–2021

Collection of :class:`_expression.ColumnElement` instances, typically for :class:`_sql.FromClause` objects. The :class:`_sql.ColumnCollection` object is most commonly available as the :attr:`_schema.Table.c` or :attr:`_schema.Table.columns` collection on the :class:`_schema.Tabl

class ColumnCollection(Generic[_COLKEY, _COL_co]):
    """Collection of :class:`_expression.ColumnElement` instances,
    typically for
    :class:`_sql.FromClause` objects.

    The :class:`_sql.ColumnCollection` object is most commonly available
    as the :attr:`_schema.Table.c` or :attr:`_schema.Table.columns` collection
    on the :class:`_schema.Table` object, introduced at
    :ref:`metadata_tables_and_columns`.

    The :class:`_expression.ColumnCollection` has both mapping- and sequence-
    like behaviors. A :class:`_expression.ColumnCollection` usually stores
    :class:`_schema.Column` objects, which are then accessible both via mapping
    style access as well as attribute access style.

    To access :class:`_schema.Column` objects using ordinary attribute-style
    access, specify the name like any other object attribute, such as below
    a column named ``employee_name`` is accessed::

        >>> employee_table.c.employee_name

    To access columns that have names with special characters or spaces,
    index-style access is used, such as below which illustrates a column named
    ``employee ' payment`` is accessed::

        >>> employee_table.c["employee ' payment"]

    As the :class:`_sql.ColumnCollection` object provides a Python dictionary
    interface, common dictionary method names like
    :meth:`_sql.ColumnCollection.keys`, :meth:`_sql.ColumnCollection.values`,
    and :meth:`_sql.ColumnCollection.items` are available, which means that
    database columns that are keyed under these names also need to use indexed
    access::

        >>> employee_table.c["values"]


    The name for which a :class:`_schema.Column` would be present is normally
    that of the :paramref:`_schema.Column.key` parameter.  In some contexts,
    such as a :class:`_sql.Select` object that uses a label style set
    using the :meth:`_sql.Select.set_label_style` method, a column of a certain
    key may instead be represented under a particular label name such
    as ``tablename_columnname``::

        >>> from sqlalchemy import select, column, table
        >>> from sqlalchemy import LABEL_STYLE_TABLENAME_PLUS_COL
        >>> t = table("t", column("c"))
        >>> stmt = select(t).set_label_style(LABEL_STYLE_TABLENAME_PLUS_COL)
        >>> subq = stmt.subquery()
        >>> subq.c.t_c
        <sqlalchemy.sql.elements.ColumnClause at 0x7f59dcf04fa0; t_c>

    :class:`.ColumnCollection` also indexes the columns in order and allows
    them to be accessible by their integer position::

        >>> cc[0]
        Column('x', Integer(), table=None)
        >>> cc[1]