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편집 파일: api.py

# ext/declarative/api.py # Copyright (C) 2005-2019 the SQLAlchemy authors and contributors # <see AUTHORS file> # # This module is part of SQLAlchemy and is released under # the MIT License: http://www.opensource.org/licenses/mit-license.php """Public API functions and helpers for declarative.""" import re import weakref from .base import _add_attribute from .base import _as_declarative from .base import _declarative_constructor from .base import _DeferredMapperConfig from .base import _del_attribute from .clsregistry import _class_resolver from ... import exc from ... import inspection from ... import util from ...orm import attributes from ...orm import comparable_property from ...orm import exc as orm_exc from ...orm import interfaces from ...orm import properties from ...orm import synonym as _orm_synonym from ...orm.base import _inspect_mapped_class from ...orm.base import _mapper_or_none from ...orm.util import polymorphic_union from ...schema import MetaData from ...schema import Table from ...util import hybridmethod from ...util import hybridproperty from ...util import OrderedDict def instrument_declarative(cls, registry, metadata): """Given a class, configure the class declaratively, using the given registry, which can be any dictionary, and MetaData object. """ if "_decl_class_registry" in cls.__dict__: raise exc.InvalidRequestError( "Class %r already has been " "instrumented declaratively" % cls ) cls._decl_class_registry = registry cls.metadata = metadata _as_declarative(cls, cls.__name__, cls.__dict__) def has_inherited_table(cls): """Given a class, return True if any of the classes it inherits from has a mapped table, otherwise return False. This is used in declarative mixins to build attributes that behave differently for the base class vs. a subclass in an inheritance hierarchy. .. seealso:: :ref:`decl_mixin_inheritance` """ for class_ in cls.__mro__[1:]: if getattr(class_, "__table__", None) is not None: return True return False class DeclarativeMeta(type): def __init__(cls, classname, bases, dict_): if "_decl_class_registry" not in cls.__dict__: _as_declarative(cls, classname, cls.__dict__) type.__init__(cls, classname, bases, dict_) def __setattr__(cls, key, value): _add_attribute(cls, key, value) def __delattr__(cls, key): _del_attribute(cls, key) def synonym_for(name, map_column=False): """Decorator that produces an :func:`.orm.synonym` attribute in conjunction with a Python descriptor. The function being decorated is passed to :func:`.orm.synonym` as the :paramref:`.orm.synonym.descriptor` parameter:: class MyClass(Base): __tablename__ = 'my_table' id = Column(Integer, primary_key=True) _job_status = Column("job_status", String(50)) @synonym_for("job_status") @property def job_status(self): return "Status: %s" % self._job_status The :ref:`hybrid properties <mapper_hybrids>` feature of SQLAlchemy is typically preferred instead of synonyms, which is a more legacy feature. .. seealso:: :ref:`synonyms` - Overview of synonyms :func:`.orm.synonym` - the mapper-level function :ref:`mapper_hybrids` - The Hybrid Attribute extension provides an updated approach to augmenting attribute behavior more flexibly than can be achieved with synonyms. """ def decorate(fn): return _orm_synonym(name, map_column=map_column, descriptor=fn) return decorate def comparable_using(comparator_factory): """Decorator, allow a Python @property to be used in query criteria. This is a decorator front end to :func:`~sqlalchemy.orm.comparable_property` that passes through the comparator_factory and the function being decorated:: @comparable_using(MyComparatorType) @property def prop(self): return 'special sauce' The regular ``comparable_property()`` is also usable directly in a declarative setting and may be convenient for read/write properties:: prop = comparable_property(MyComparatorType) """ def decorate(fn): return comparable_property(comparator_factory, fn) return decorate class declared_attr(interfaces._MappedAttribute, property): """Mark a class-level method as representing the definition of a mapped property or special declarative member name. @declared_attr turns the attribute into a scalar-like property that can be invoked from the uninstantiated class. Declarative treats attributes specifically marked with @declared_attr as returning a construct that is specific to mapping or declarative table configuration. The name of the attribute is that of what the non-dynamic version of the attribute would be. @declared_attr is more often than not applicable to mixins, to define relationships that are to be applied to different implementors of the class:: class ProvidesUser(object): "A mixin that adds a 'user' relationship to classes." @declared_attr def user(self): return relationship("User") It also can be applied to mapped classes, such as to provide a "polymorphic" scheme for inheritance:: class Employee(Base): id = Column(Integer, primary_key=True) type = Column(String(50), nullable=False) @declared_attr def __tablename__(cls): return cls.__name__.lower() @declared_attr def __mapper_args__(cls): if cls.__name__ == 'Employee': return { "polymorphic_on":cls.type, "polymorphic_identity":"Employee" } else: return {"polymorphic_identity":cls.__name__} """ def __init__(self, fget, cascading=False): super(declared_attr, self).__init__(fget) self.__doc__ = fget.__doc__ self._cascading = cascading def __get__(desc, self, cls): reg = cls.__dict__.get("_sa_declared_attr_reg", None) if reg is None: if ( not re.match(r"^__.+__$", desc.fget.__name__) and attributes.manager_of_class(cls) is None ): util.warn( "Unmanaged access of declarative attribute %s from " "non-mapped class %s" % (desc.fget.__name__, cls.__name__) ) return desc.fget(cls) elif desc in reg: return reg[desc] else: reg[desc] = obj = desc.fget(cls) return obj @hybridmethod def _stateful(cls, **kw): return _stateful_declared_attr(**kw) @hybridproperty def cascading(cls): """Mark a :class:`.declared_attr` as cascading. This is a special-use modifier which indicates that a column or MapperProperty-based declared attribute should be configured distinctly per mapped subclass, within a mapped-inheritance scenario. .. warning:: The :attr:`.declared_attr.cascading` modifier has several limitations: * The flag **only** applies to the use of :class:`.declared_attr` on declarative mixin classes and ``__abstract__`` classes; it currently has no effect when used on a mapped class directly. * The flag **only** applies to normally-named attributes, e.g. not any special underscore attributes such as ``__tablename__``. On these attributes it has **no** effect. * The flag currently **does not allow further overrides** down the class hierarchy; if a subclass tries to override the attribute, a warning is emitted and the overridden attribute is skipped. This is a limitation that it is hoped will be resolved at some point. Below, both MyClass as well as MySubClass will have a distinct ``id`` Column object established:: class HasIdMixin(object): @declared_attr.cascading def id(cls): if has_inherited_table(cls): return Column( ForeignKey('myclass.id'), primary_key=True) else: return Column(Integer, primary_key=True) class MyClass(HasIdMixin, Base): __tablename__ = 'myclass' # ... class MySubClass(MyClass): "" # ... The behavior of the above configuration is that ``MySubClass`` will refer to both its own ``id`` column as well as that of ``MyClass`` underneath the attribute named ``some_id``. .. seealso:: :ref:`declarative_inheritance` :ref:`mixin_inheritance_columns` """ return cls._stateful(cascading=True) class _stateful_declared_attr(declared_attr): def __init__(self, **kw): self.kw = kw def _stateful(self, **kw): new_kw = self.kw.copy() new_kw.update(kw) return _stateful_declared_attr(**new_kw) def __call__(self, fn): return declared_attr(fn, **self.kw) def declarative_base( bind=None, metadata=None, mapper=None, cls=object, name="Base", constructor=_declarative_constructor, class_registry=None, metaclass=DeclarativeMeta, ): r"""Construct a base class for declarative class definitions. The new base class will be given a metaclass that produces appropriate :class:`~sqlalchemy.schema.Table` objects and makes the appropriate :func:`~sqlalchemy.orm.mapper` calls based on the information provided declaratively in the class and any subclasses of the class. :param bind: An optional :class:`~sqlalchemy.engine.Connectable`, will be assigned the ``bind`` attribute on the :class:`~sqlalchemy.schema.MetaData` instance. :param metadata: An optional :class:`~sqlalchemy.schema.MetaData` instance. All :class:`~sqlalchemy.schema.Table` objects implicitly declared by subclasses of the base will share this MetaData. A MetaData instance will be created if none is provided. The :class:`~sqlalchemy.schema.MetaData` instance will be available via the `metadata` attribute of the generated declarative base class. :param mapper: An optional callable, defaults to :func:`~sqlalchemy.orm.mapper`. Will be used to map subclasses to their Tables. :param cls: Defaults to :class:`object`. A type to use as the base for the generated declarative base class. May be a class or tuple of classes. :param name: Defaults to ``Base``. The display name for the generated class. Customizing this is not required, but can improve clarity in tracebacks and debugging. :param constructor: Defaults to :func:`~sqlalchemy.ext.declarative.base._declarative_constructor`, an __init__ implementation that assigns \**kwargs for declared fields and relationships to an instance. If ``None`` is supplied, no __init__ will be provided and construction will fall back to cls.__init__ by way of the normal Python semantics. :param class_registry: optional dictionary that will serve as the registry of class names-> mapped classes when string names are used to identify classes inside of :func:`.relationship` and others. Allows two or more declarative base classes to share the same registry of class names for simplified inter-base relationships. :param metaclass: Defaults to :class:`.DeclarativeMeta`. A metaclass or __metaclass__ compatible callable to use as the meta type of the generated declarative base class. .. versionchanged:: 1.1 if :paramref:`.declarative_base.cls` is a single class (rather than a tuple), the constructed base class will inherit its docstring. .. seealso:: :func:`.as_declarative` """ lcl_metadata = metadata or MetaData() if bind: lcl_metadata.bind = bind if class_registry is None: class_registry = weakref.WeakValueDictionary() bases = not isinstance(cls, tuple) and (cls,) or cls class_dict = dict( _decl_class_registry=class_registry, metadata=lcl_metadata ) if isinstance(cls, type): class_dict["__doc__"] = cls.__doc__ if constructor: class_dict["__init__"] = constructor if mapper: class_dict["__mapper_cls__"] = mapper return metaclass(name, bases, class_dict) def as_declarative(**kw): """ Class decorator for :func:`.declarative_base`. Provides a syntactical shortcut to the ``cls`` argument sent to :func:`.declarative_base`, allowing the base class to be converted in-place to a "declarative" base:: from sqlalchemy.ext.declarative import as_declarative @as_declarative() class Base(object): @declared_attr def __tablename__(cls): return cls.__name__.lower() id = Column(Integer, primary_key=True) class MyMappedClass(Base): # ... All keyword arguments passed to :func:`.as_declarative` are passed along to :func:`.declarative_base`. .. seealso:: :func:`.declarative_base` """ def decorate(cls): kw["cls"] = cls kw["name"] = cls.__name__ return declarative_base(**kw) return decorate class ConcreteBase(object): """A helper class for 'concrete' declarative mappings. :class:`.ConcreteBase` will use the :func:`.polymorphic_union` function automatically, against all tables mapped as a subclass to this class. The function is called via the ``__declare_last__()`` function, which is essentially a hook for the :meth:`.after_configured` event. :class:`.ConcreteBase` produces a mapped table for the class itself. Compare to :class:`.AbstractConcreteBase`, which does not. Example:: from sqlalchemy.ext.declarative import ConcreteBase class Employee(ConcreteBase, Base): __tablename__ = 'employee' employee_id = Column(Integer, primary_key=True) name = Column(String(50)) __mapper_args__ = { 'polymorphic_identity':'employee', 'concrete':True} class Manager(Employee): __tablename__ = 'manager' employee_id = Column(Integer, primary_key=True) name = Column(String(50)) manager_data = Column(String(40)) __mapper_args__ = { 'polymorphic_identity':'manager', 'concrete':True} .. seealso:: :class:`.AbstractConcreteBase` :ref:`concrete_inheritance` :ref:`inheritance_concrete_helpers` """ @classmethod def _create_polymorphic_union(cls, mappers): return polymorphic_union( OrderedDict( (mp.polymorphic_identity, mp.local_table) for mp in mappers ), "type", "pjoin", ) @classmethod def __declare_first__(cls): m = cls.__mapper__ if m.with_polymorphic: return mappers = list(m.self_and_descendants) pjoin = cls._create_polymorphic_union(mappers) m._set_with_polymorphic(("*", pjoin)) m._set_polymorphic_on(pjoin.c.type) class AbstractConcreteBase(ConcreteBase): """A helper class for 'concrete' declarative mappings. :class:`.AbstractConcreteBase` will use the :func:`.polymorphic_union` function automatically, against all tables mapped as a subclass to this class. The function is called via the ``__declare_last__()`` function, which is essentially a hook for the :meth:`.after_configured` event. :class:`.AbstractConcreteBase` does produce a mapped class for the base class, however it is not persisted to any table; it is instead mapped directly to the "polymorphic" selectable directly and is only used for selecting. Compare to :class:`.ConcreteBase`, which does create a persisted table for the base class. .. note:: The :class:`.AbstractConcreteBase` class does not intend to set up the mapping for the base class until all the subclasses have been defined, as it needs to create a mapping against a selectable that will include all subclass tables. In order to achieve this, it waits for the **mapper configuration event** to occur, at which point it scans through all the configured subclasses and sets up a mapping that will query against all subclasses at once. While this event is normally invoked automatically, in the case of :class:`.AbstractConcreteBase`, it may be necessary to invoke it explicitly after **all** subclass mappings are defined, if the first operation is to be a query against this base class. To do so, invoke :func:`.configure_mappers` once all the desired classes have been configured:: from sqlalchemy.orm import configure_mappers configure_mappers() .. seealso:: :func:`.orm.configure_mappers` Example:: from sqlalchemy.ext.declarative import AbstractConcreteBase class Employee(AbstractConcreteBase, Base): pass class Manager(Employee): __tablename__ = 'manager' employee_id = Column(Integer, primary_key=True) name = Column(String(50)) manager_data = Column(String(40)) __mapper_args__ = { 'polymorphic_identity':'manager', 'concrete':True} configure_mappers() The abstract base class is handled by declarative in a special way; at class configuration time, it behaves like a declarative mixin or an ``__abstract__`` base class. Once classes are configured and mappings are produced, it then gets mapped itself, but after all of its descendants. This is a very unique system of mapping not found in any other SQLAlchemy system. Using this approach, we can specify columns and properties that will take place on mapped subclasses, in the way that we normally do as in :ref:`declarative_mixins`:: class Company(Base): __tablename__ = 'company' id = Column(Integer, primary_key=True) class Employee(AbstractConcreteBase, Base): employee_id = Column(Integer, primary_key=True) @declared_attr def company_id(cls): return Column(ForeignKey('company.id')) @declared_attr def company(cls): return relationship("Company") class Manager(Employee): __tablename__ = 'manager' name = Column(String(50)) manager_data = Column(String(40)) __mapper_args__ = { 'polymorphic_identity':'manager', 'concrete':True} configure_mappers() When we make use of our mappings however, both ``Manager`` and ``Employee`` will have an independently usable ``.company`` attribute:: session.query(Employee).filter(Employee.company.has(id=5)) .. versionchanged:: 1.0.0 - The mechanics of :class:`.AbstractConcreteBase` have been reworked to support relationships established directly on the abstract base, without any special configurational steps. .. seealso:: :class:`.ConcreteBase` :ref:`concrete_inheritance` :ref:`inheritance_concrete_helpers` """ __no_table__ = True @classmethod def __declare_first__(cls): cls._sa_decl_prepare_nocascade() @classmethod def _sa_decl_prepare_nocascade(cls): if getattr(cls, "__mapper__", None): return to_map = _DeferredMapperConfig.config_for_cls(cls) # can't rely on 'self_and_descendants' here # since technically an immediate subclass # might not be mapped, but a subclass # may be. mappers = [] stack = list(cls.__subclasses__()) while stack: klass = stack.pop() stack.extend(klass.__subclasses__()) mn = _mapper_or_none(klass) if mn is not None: mappers.append(mn) pjoin = cls._create_polymorphic_union(mappers) # For columns that were declared on the class, these # are normally ignored with the "__no_table__" mapping, # unless they have a different attribute key vs. col name # and are in the properties argument. # In that case, ensure we update the properties entry # to the correct column from the pjoin target table. declared_cols = set(to_map.declared_columns) for k, v in list(to_map.properties.items()): if v in declared_cols: to_map.properties[k] = pjoin.c[v.key] to_map.local_table = pjoin m_args = to_map.mapper_args_fn or dict def mapper_args(): args = m_args() args["polymorphic_on"] = pjoin.c.type return args to_map.mapper_args_fn = mapper_args m = to_map.map() for scls in cls.__subclasses__(): sm = _mapper_or_none(scls) if sm and sm.concrete and cls in scls.__bases__: sm._set_concrete_base(m) @classmethod def _sa_raise_deferred_config(cls): raise orm_exc.UnmappedClassError( cls, msg="Class %s is a subclass of AbstractConcreteBase and " "has a mapping pending until all subclasses are defined. " "Call the sqlalchemy.orm.configure_mappers() function after " "all subclasses have been defined to " "complete the mapping of this class." % orm_exc._safe_cls_name(cls), ) class DeferredReflection(object): """A helper class for construction of mappings based on a deferred reflection step. Normally, declarative can be used with reflection by setting a :class:`.Table` object using autoload=True as the ``__table__`` attribute on a declarative class. The caveat is that the :class:`.Table` must be fully reflected, or at the very least have a primary key column, at the point at which a normal declarative mapping is constructed, meaning the :class:`.Engine` must be available at class declaration time. The :class:`.DeferredReflection` mixin moves the construction of mappers to be at a later point, after a specific method is called which first reflects all :class:`.Table` objects created so far. Classes can define it as such:: from sqlalchemy.ext.declarative import declarative_base from sqlalchemy.ext.declarative import DeferredReflection Base = declarative_base() class MyClass(DeferredReflection, Base): __tablename__ = 'mytable' Above, ``MyClass`` is not yet mapped. After a series of classes have been defined in the above fashion, all tables can be reflected and mappings created using :meth:`.prepare`:: engine = create_engine("someengine://...") DeferredReflection.prepare(engine) The :class:`.DeferredReflection` mixin can be applied to individual classes, used as the base for the declarative base itself, or used in a custom abstract class. Using an abstract base allows that only a subset of classes to be prepared for a particular prepare step, which is necessary for applications that use more than one engine. For example, if an application has two engines, you might use two bases, and prepare each separately, e.g.:: class ReflectedOne(DeferredReflection, Base): __abstract__ = True class ReflectedTwo(DeferredReflection, Base): __abstract__ = True class MyClass(ReflectedOne): __tablename__ = 'mytable' class MyOtherClass(ReflectedOne): __tablename__ = 'myothertable' class YetAnotherClass(ReflectedTwo): __tablename__ = 'yetanothertable' # ... etc. Above, the class hierarchies for ``ReflectedOne`` and ``ReflectedTwo`` can be configured separately:: ReflectedOne.prepare(engine_one) ReflectedTwo.prepare(engine_two) """ @classmethod def prepare(cls, engine): """Reflect all :class:`.Table` objects for all current :class:`.DeferredReflection` subclasses""" to_map = _DeferredMapperConfig.classes_for_base(cls) for thingy in to_map: cls._sa_decl_prepare(thingy.local_table, engine) thingy.map() mapper = thingy.cls.__mapper__ metadata = mapper.class_.metadata for rel in mapper._props.values(): if ( isinstance(rel, properties.RelationshipProperty) and rel.secondary is not None ): if isinstance(rel.secondary, Table): cls._reflect_table(rel.secondary, engine) elif isinstance(rel.secondary, _class_resolver): rel.secondary._resolvers += ( cls._sa_deferred_table_resolver(engine, metadata), ) @classmethod def _sa_deferred_table_resolver(cls, engine, metadata): def _resolve(key): t1 = Table(key, metadata) cls._reflect_table(t1, engine) return t1 return _resolve @classmethod def _sa_decl_prepare(cls, local_table, engine): # autoload Table, which is already # present in the metadata. This # will fill in db-loaded columns # into the existing Table object. if local_table is not None: cls._reflect_table(local_table, engine) @classmethod def _sa_raise_deferred_config(cls): raise orm_exc.UnmappedClassError( cls, msg="Class %s is a subclass of DeferredReflection. " "Mappings are not produced until the .prepare() " "method is called on the class hierarchy." % orm_exc._safe_cls_name(cls), ) @classmethod def _reflect_table(cls, table, engine): Table( table.name, table.metadata, extend_existing=True, autoload_replace=False, autoload=True, autoload_with=engine, schema=table.schema, ) @inspection._inspects(DeclarativeMeta) def _inspect_decl_meta(cls): mp = _inspect_mapped_class(cls) if mp is None: if _DeferredMapperConfig.has_cls(cls): _DeferredMapperConfig.raise_unmapped_for_cls(cls) raise orm_exc.UnmappedClassError( cls, msg="Class %s has a deferred mapping on it. It is not yet " "usable as a mapped class." % orm_exc._safe_cls_name(cls), ) return mp