title: sqlalchemy.orm class_mapper Example Code
category: page
slug: sqlalchemy-orm-class-mapper-examples
sortorder: 500031064
toc: False
sidebartitle: sqlalchemy.orm class_mapper
meta: Python example code that shows how to use the class_mapper callable from the sqlalchemy.orm module of the SQLAlchemy project.


`class_mapper` is a callable within the `sqlalchemy.orm` module of the SQLAlchemy project.

<a href="/sqlalchemy-orm-columnproperty-examples.html">ColumnProperty</a>,
<a href="/sqlalchemy-orm-compositeproperty-examples.html">CompositeProperty</a>,
<a href="/sqlalchemy-orm-load-examples.html">Load</a>,
<a href="/sqlalchemy-orm-mapper-examples.html">Mapper</a>,
<a href="/sqlalchemy-orm-query-examples.html">Query</a>,
<a href="/sqlalchemy-orm-relationshipproperty-examples.html">RelationshipProperty</a>,
<a href="/sqlalchemy-orm-session-examples.html">Session</a>,
<a href="/sqlalchemy-orm-synonymproperty-examples.html">SynonymProperty</a>,
<a href="/sqlalchemy-orm-aliased-examples.html">aliased</a>,
<a href="/sqlalchemy-orm-attributes-examples.html">attributes</a>,
<a href="/sqlalchemy-orm-backref-examples.html">backref</a>,
<a href="/sqlalchemy-orm-column-property-examples.html">column_property</a>,
<a href="/sqlalchemy-orm-composite-examples.html">composite</a>,
<a href="/sqlalchemy-orm-interfaces-examples.html">interfaces</a>,
<a href="/sqlalchemy-orm-mapper-examples.html">mapper</a>,
<a href="/sqlalchemy-orm-mapperlib-examples.html">mapperlib</a>,
<a href="/sqlalchemy-orm-object-mapper-examples.html">object_mapper</a>,
<a href="/sqlalchemy-orm-object-session-examples.html">object_session</a>,
<a href="/sqlalchemy-orm-query-examples.html">query</a>,
<a href="/sqlalchemy-orm-relationship-examples.html">relationship</a>,
<a href="/sqlalchemy-orm-session-examples.html">session</a>,
<a href="/sqlalchemy-orm-sessionmaker-examples.html">sessionmaker</a>,
and <a href="/sqlalchemy-orm-strategies-examples.html">strategies</a>
are several other callables with code examples from the same `sqlalchemy.orm` package.

## Example 1 from graphene-sqlalchemy
[graphene-sqlalchemy](https://github.com/graphql-python/graphene-sqlalchemy)
([project documentation](https://docs.graphene-python.org/projects/sqlalchemy/en/latest/)
and
[PyPI package information](https://pypi.org/project/graphene-sqlalchemy/))
is a [SQLAlchemy](/sqlalchemy.html) integration for
[Graphene](https://graphene-python.org/), which makes it easier to build
GraphQL-based [APIs](/application-programming-interfaces.html) into Python
[web applications](/web-development.html). The package allows you to
subclass SQLAlchemy classes and build queries around them with custom
code to match the backend queries with the GraphQL-based request queries.
The project is provided as open source under the
[MIT license](https://github.com/graphql-python/graphene-sqlalchemy/blob/master/LICENSE.md).

[**graphene-sqlalchemy / graphene_sqlalchemy / utils.py**](https://github.com/graphql-python/graphene-sqlalchemy/blob/master/graphene_sqlalchemy/./utils.py)

```python
# utils.py
import re
import warnings

from sqlalchemy.exc import ArgumentError
~~from sqlalchemy.orm import class_mapper, object_mapper
from sqlalchemy.orm.exc import UnmappedClassError, UnmappedInstanceError


def get_session(context):
    return context.get("session")


def get_query(model, context):
    query = getattr(model, "query", None)
    if not query:
        session = get_session(context)
        if not session:
            raise Exception(
                "A query in the model Base or a session in the schema is required for querying.\n"
                "Read more http://docs.graphene-python.org/projects/sqlalchemy/en/latest/tips/#querying"
            )
        query = session.query(model)
    return query


def is_mapped_class(cls):
    try:
~~        class_mapper(cls)
    except (ArgumentError, UnmappedClassError):
        return False
    else:
        return True


def is_mapped_instance(cls):
    try:
        object_mapper(cls)
    except (ArgumentError, UnmappedInstanceError):
        return False
    else:
        return True


def to_type_name(name):
    return "".join(part[:1].upper() + part[1:] for part in name.split("_"))


_re_enum_value_name_1 = re.compile("(.)([A-Z][a-z]+)")
_re_enum_value_name_2 = re.compile("([a-z0-9])([A-Z])")


def to_enum_value_name(name):


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

```


## Example 2 from sqlalchemy-utils
[sqlalchemy-utils](https://github.com/kvesteri/sqlalchemy-utils)
([project documentation](https://sqlalchemy-utils.readthedocs.io/en/latest/)
and
[PyPI package information](https://pypi.org/project/SQLAlchemy-Utils/))
is a code library with various helper functions and new data types
that make it easier to use [SQLAlchemy](/sqlalchemy.html) when building
projects that involve more specific storage requirements such as
[currency](https://sqlalchemy-utils.readthedocs.io/en/latest/data_types.html#module-sqlalchemy_utils.types.currency).
The wide array of
[data types](https://sqlalchemy-utils.readthedocs.io/en/latest/data_types.html)
includes [ranged values](https://sqlalchemy-utils.readthedocs.io/en/latest/range_data_types.html)
and [aggregated attributes](https://sqlalchemy-utils.readthedocs.io/en/latest/aggregates.html).

[**sqlalchemy-utils / sqlalchemy_utils / generic.py**](https://github.com/kvesteri/sqlalchemy-utils/blob/master/sqlalchemy_utils/./generic.py)

```python
# generic.py
from collections.abc import Iterable

import six
import sqlalchemy as sa
from sqlalchemy.ext.hybrid import hybrid_property
~~from sqlalchemy.orm import attributes, class_mapper, ColumnProperty
from sqlalchemy.orm.interfaces import MapperProperty, PropComparator
from sqlalchemy.orm.session import _state_session
from sqlalchemy.util import set_creation_order

from .exceptions import ImproperlyConfigured
from .functions import identity


class GenericAttributeImpl(attributes.ScalarAttributeImpl):
    def get(self, state, dict_, passive=attributes.PASSIVE_OFF):
        if self.key in dict_:
            return dict_[self.key]

        session = _state_session(state)
        if session is None:
            return None

        discriminator = self.get_state_discriminator(state)
        target_class = state.class_._decl_class_registry.get(discriminator)

        if target_class is None:
            return None

        id = self.get_state_id(state)


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


        return target

    def get_state_discriminator(self, state):
        discriminator = self.parent_token.discriminator
        if isinstance(discriminator, hybrid_property):
            return getattr(state.obj(), discriminator.__name__)
        else:
            return state.attrs[discriminator.key].value

    def get_state_id(self, state):
        return tuple(state.attrs[id.key].value for id in self.parent_token.id)

    def set(self, state, dict_, initiator,
            passive=attributes.PASSIVE_OFF,
            check_old=None,
            pop=False):

        dict_[self.key] = initiator

        if initiator is None:
            for id in self.parent_token.id:
                dict_[id.key] = None
            dict_[self.parent_token.discriminator.key] = None
        else:
            class_ = type(initiator)
~~            mapper = class_mapper(class_)

            pk = mapper.identity_key_from_instance(initiator)[1]

            discriminator = six.text_type(class_.__name__)

            for index, id in enumerate(self.parent_token.id):
                dict_[id.key] = pk[index]
            dict_[self.parent_token.discriminator.key] = discriminator


class GenericRelationshipProperty(MapperProperty):

    def __init__(self, discriminator, id, doc=None):
        super(GenericRelationshipProperty, self).__init__()
        self._discriminator_col = discriminator
        self._id_cols = id
        self._id = None
        self._discriminator = None
        self.doc = doc

        set_creation_order(self)

    def _column_to_property(self, column):
        if isinstance(column, hybrid_property):


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

```

