sqlalchemy.schema CheckConstraint Example Code

CheckConstraint is a class within the sqlalchemy.schema module of the SQLAlchemy project.

Column, CreateIndex, CreateTable, DDLElement, ForeignKey, ForeignKeyConstraint, Index, PrimaryKeyConstraint, and Table are several other callables with code examples from the same sqlalchemy.schema package.

Example 1 from alembic

Alembic (project documentation and PyPI page) is a data migrations tool used with SQLAlchemy to make database schema changes. The Alembic project is open sourced under the MIT license.

alembic / alembic / util / sqla_compat.py

# sqla_compat.py
import re

from sqlalchemy import __version__
from sqlalchemy import inspect
from sqlalchemy import schema
from sqlalchemy import sql
from sqlalchemy import types as sqltypes
from sqlalchemy.ext.compiler import compiles
from sqlalchemy.schema import CheckConstraint
from sqlalchemy.schema import Column
from sqlalchemy.schema import ForeignKeyConstraint
from sqlalchemy.sql.elements import quoted_name
from sqlalchemy.sql.expression import _BindParamClause
from sqlalchemy.sql.expression import _TextClause as TextClause
from sqlalchemy.sql.visitors import traverse

from . import compat


def _safe_int(value):
    try:
        return int(value)
    except:
        return value


_vers = tuple(
    [_safe_int(x) for x in re.findall(r"(\d+|[abc]\d)", __version__)]
)
sqla_110 = _vers >= (1, 1, 0)
sqla_1115 = _vers >= (1, 1, 15)
sqla_120 = _vers >= (1, 2, 0)
sqla_1216 = _vers >= (1, 2, 16)


## ... source file abbreviated to get to CheckConstraint examples ...


def _exec_on_inspector(inspector, statement, **params):
    if sqla_14:
        with inspector._operation_context() as conn:
            return conn.execute(statement, params)
    else:
        return inspector.bind.execute(statement, params)


def _server_default_is_computed(column):
    if not has_computed:
        return False
    else:
        return isinstance(column.computed, Computed)


def _table_for_constraint(constraint):
    if isinstance(constraint, ForeignKeyConstraint):
        return constraint.parent
    else:
        return constraint.table


def _columns_for_constraint(constraint):
    if isinstance(constraint, ForeignKeyConstraint):
        return [fk.parent for fk in constraint.elements]
    elif isinstance(constraint, CheckConstraint):
        return _find_columns(constraint.sqltext)
    else:
        return list(constraint.columns)


def _fk_spec(constraint):
    source_columns = [
        constraint.columns[key].name for key in constraint.column_keys
    ]

    source_table = constraint.parent.name
    source_schema = constraint.parent.schema
    target_schema = constraint.elements[0].column.table.schema
    target_table = constraint.elements[0].column.table.name
    target_columns = [element.column.name for element in constraint.elements]
    ondelete = constraint.ondelete
    onupdate = constraint.onupdate
    deferrable = constraint.deferrable
    initially = constraint.initially
    return (
        source_schema,
        source_table,
        source_columns,
        target_schema,


## ... source file continues with no further CheckConstraint examples...

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