sqlalchemy-orm-object-session.markdown

title: sqlalchemy.orm object_session Example Code category: page slug: sqlalchemy-orm-object-session-examples sortorder: 500031071 toc: False sidebartitle: sqlalchemy.orm object_session meta: Python example code that shows how to use the object_session callable from the sqlalchemy.orm module of the SQLAlchemy project.

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

ColumnProperty, CompositeProperty, Load, Mapper, Query, RelationshipProperty, Session, SynonymProperty, aliased, attributes, backref, class_mapper, column_property, composite, interfaces, mapper, mapperlib, object_mapper, query, relationship, session, sessionmaker, and strategies are several other callables with code examples from the same sqlalchemy.orm package.

Example 1 from sqlalchemy-utils

sqlalchemy-utils (project documentation and PyPI package information) is a code library with various helper functions and new data types that make it easier to use SQLAlchemy when building projects that involve more specific storage requirements such as currency. The wide array of data types includes ranged values and aggregated attributes.

sqlalchemy-utils / sqlalchemy_utils / functions / foreign_keys.py

# foreign_keys.py
from collections import defaultdict
from itertools import groupby

import sqlalchemy as sa
from sqlalchemy.exc import NoInspectionAvailable
~~from sqlalchemy.orm import object_session
from sqlalchemy.schema import ForeignKeyConstraint, MetaData, Table

from ..query_chain import QueryChain
from .database import has_index
from .orm import get_column_key, get_mapper, get_tables


def get_foreign_key_values(fk, obj):
    return dict(
        (
            fk.constraint.columns.values()[index].key,
            getattr(obj, element.column.key)
        )
        for
        index, element
        in
        enumerate(fk.constraint.elements)
    )


def group_foreign_keys(foreign_keys):
    foreign_keys = sorted(
        foreign_keys, key=lambda key: key.constraint.table.name
    )
    return groupby(foreign_keys, lambda key: key.constraint.table)


def get_referencing_foreign_keys(mixed):
    if isinstance(mixed, sa.Table):
        tables = [mixed]
    else:
        tables = get_tables(mixed)

    referencing_foreign_keys = set()

    for table in mixed.metadata.tables.values():
        if table not in tables:
            for constraint in table.constraints:
                if isinstance(constraint, sa.sql.schema.ForeignKeyConstraint):
                    for fk in constraint.elements:
                        if any(fk.references(t) for t in tables):
                            referencing_foreign_keys.add(fk)
    return referencing_foreign_keys


def merge_references(from_, to, foreign_keys=None):
    if from_.__tablename__ != to.__tablename__:
        raise TypeError('The tables of given arguments do not match.')

~~    session = object_session(from_)
    foreign_keys = get_referencing_foreign_keys(from_)

    for fk in foreign_keys:
        old_values = get_foreign_key_values(fk, from_)
        new_values = get_foreign_key_values(fk, to)
        criteria = (
            getattr(fk.constraint.table.c, key) == value
            for key, value in old_values.items()
        )
        try:
            mapper = get_mapper(fk.constraint.table)
        except ValueError:
            query = (
                fk.constraint.table
                .update()
                .where(sa.and_(*criteria))
                .values(new_values)
            )
            session.execute(query)
        else:
            (
                session.query(mapper.class_)
                .filter_by(**old_values)
                .update(
                    new_values,
                    'evaluate'
                )
            )


def dependent_objects(obj, foreign_keys=None):
    if foreign_keys is None:
        foreign_keys = get_referencing_foreign_keys(obj)

~~    session = object_session(obj)

    chain = QueryChain([])
    classes = obj.__class__._decl_class_registry

    for table, keys in group_foreign_keys(foreign_keys):
        keys = list(keys)
        for class_ in classes.values():
            try:
                mapper = sa.inspect(class_)
            except NoInspectionAvailable:
                continue
            parent_mapper = mapper.inherits
            if (
                table in mapper.tables and
                not (parent_mapper and table in parent_mapper.tables)
            ):
                query = session.query(class_).filter(
                    sa.or_(*_get_criteria(keys, class_, obj))
                )
                chain.queries.append(query)
    return chain


def _get_criteria(keys, class_, obj):


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