sqlalchemy.orm.properties RelationshipProperty Example Code

RelationshipProperty is a class within the sqlalchemy.orm.properties module of the SQLAlchemy project.

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 / orm.py

# orm.py
from collections import OrderedDict
from functools import partial
from inspect import isclass
from operator import attrgetter

import six
import sqlalchemy as sa
from sqlalchemy.engine.interfaces import Dialect
from sqlalchemy.ext.hybrid import hybrid_property
from sqlalchemy.orm import mapperlib
from sqlalchemy.orm.attributes import InstrumentedAttribute
from sqlalchemy.orm.exc import UnmappedInstanceError
from sqlalchemy.orm.properties import ColumnProperty, RelationshipProperty
from sqlalchemy.orm.query import _ColumnEntity
from sqlalchemy.orm.session import object_session
from sqlalchemy.orm.util import AliasedInsp

from ..utils import is_sequence


def get_class_by_table(base, table, data=None):
    found_classes = set(
        c for c in base._decl_class_registry.values()
        if hasattr(c, '__table__') and c.__table__ is table
    )
    if len(found_classes) > 1:
        if not data:
            raise ValueError(
                "Multiple declarative classes found for table '{0}'. "
                "Please provide data parameter for this function to be able "
                "to determine polymorphic scenarios.".format(
                    table.name
                )
            )
        else:
            for cls in found_classes:
                mapper = sa.inspect(cls)
                polymorphic_on = mapper.polymorphic_on.name
                if polymorphic_on in data:
                    if data[polymorphic_on] == mapper.polymorphic_identity:
                        return cls
            raise ValueError(
                "Multiple declarative classes found for table '{0}'. Given "
                "data row does not match any polymorphic identity of the "
                "found classes.".format(
                    table.name
                )
            )
    elif found_classes:
        return found_classes.pop()
    return None


def get_type(expr):
    if hasattr(expr, 'type'):
        return expr.type
    elif isinstance(expr, InstrumentedAttribute):
        expr = expr.property

    if isinstance(expr, ColumnProperty):
        return expr.columns[0].type
    elif isinstance(expr, RelationshipProperty):
        return expr.mapper.class_
    raise TypeError("Couldn't inspect type.")


def cast_if(expression, type_):
    try:
        expr_type = get_type(expression)
    except TypeError:
        expr_type = expression
        check_type = type_().python_type
    else:
        check_type = type_

    return (
        sa.cast(expression, type_)
        if not isinstance(expr_type, check_type)
        else expression
    )


def get_column_key(model, column):
    mapper = sa.inspect(model)
    try:
        return mapper.get_property_by_column(column).key


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

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