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baked.py
# sqlalchemy/ext/baked.py # Copyright (C) 2005-2021 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 """Baked query extension. Provides a creational pattern for the :class:`.query.Query` object which allows the fully constructed object, Core select statement, and string compiled result to be fully cached. """ import copy import logging from .. import exc as sa_exc from .. import util from ..orm import exc as orm_exc from ..orm import strategy_options from ..orm.query import Query from ..orm.session import Session from ..sql import func from ..sql import literal_column from ..sql import util as sql_util log = logging.getLogger(__name__) class Bakery(object): """Callable which returns a :class:`.BakedQuery`. This object is returned by the class method :meth:`.BakedQuery.bakery`. It exists as an object so that the "cache" can be easily inspected. .. versionadded:: 1.2 """ __slots__ = "cls", "cache" def __init__(self, cls_, cache): self.cls = cls_ self.cache = cache def __call__(self, initial_fn, *args): return self.cls(self.cache, initial_fn, args) class BakedQuery(object): """A builder object for :class:`.query.Query` objects.""" __slots__ = "steps", "_bakery", "_cache_key", "_spoiled" def __init__(self, bakery, initial_fn, args=()): self._cache_key = () self._update_cache_key(initial_fn, args) self.steps = [initial_fn] self._spoiled = False self._bakery = bakery @classmethod def bakery(cls, size=200, _size_alert=None): """Construct a new bakery. :return: an instance of :class:`.Bakery` """ return Bakery(cls, util.LRUCache(size, size_alert=_size_alert)) def _clone(self): b1 = BakedQuery.__new__(BakedQuery) b1._cache_key = self._cache_key b1.steps = list(self.steps) b1._bakery = self._bakery b1._spoiled = self._spoiled return b1 def _update_cache_key(self, fn, args=()): self._cache_key += (fn.__code__,) + args def __iadd__(self, other): if isinstance(other, tuple): self.add_criteria(*other) else: self.add_criteria(other) return self def __add__(self, other): if isinstance(other, tuple): return self.with_criteria(*other) else: return self.with_criteria(other) def add_criteria(self, fn, *args): """Add a criteria function to this :class:`.BakedQuery`. This is equivalent to using the ``+=`` operator to modify a :class:`.BakedQuery` in-place. """ self._update_cache_key(fn, args) self.steps.append(fn) return self def with_criteria(self, fn, *args): """Add a criteria function to a :class:`.BakedQuery` cloned from this one. This is equivalent to using the ``+`` operator to produce a new :class:`.BakedQuery` with modifications. """ return self._clone().add_criteria(fn, *args) def for_session(self, session): """Return a :class:`.Result` object for this :class:`.BakedQuery`. This is equivalent to calling the :class:`.BakedQuery` as a Python callable, e.g. ``result = my_baked_query(session)``. """ return Result(self, session) def __call__(self, session): return self.for_session(session) def spoil(self, full=False): """Cancel any query caching that will occur on this BakedQuery object. The BakedQuery can continue to be used normally, however additional creational functions will not be cached; they will be called on every invocation. This is to support the case where a particular step in constructing a baked query disqualifies the query from being cacheable, such as a variant that relies upon some uncacheable value. :param full: if False, only functions added to this :class:`.BakedQuery` object subsequent to the spoil step will be non-cached; the state of the :class:`.BakedQuery` up until this point will be pulled from the cache. If True, then the entire :class:`_query.Query` object is built from scratch each time, with all creational functions being called on each invocation. """ if not full and not self._spoiled: _spoil_point = self._clone() _spoil_point._cache_key += ("_query_only",) self.steps = [_spoil_point._retrieve_baked_query] self._spoiled = True return self def _effective_key(self, session): """Return the key that actually goes into the cache dictionary for this :class:`.BakedQuery`, taking into account the given :class:`.Session`. This basically means we also will include the session's query_class, as the actual :class:`_query.Query` object is part of what's cached and needs to match the type of :class:`_query.Query` that a later session will want to use. """ return self._cache_key + (session._query_cls,) def _with_lazyload_options(self, options, effective_path, cache_path=None): """Cloning version of _add_lazyload_options.""" q = self._clone() q._add_lazyload_options(options, effective_path, cache_path=cache_path) return q def _add_lazyload_options(self, options, effective_path, cache_path=None): """Used by per-state lazy loaders to add options to the "lazy load" query from a parent query. Creates a cache key based on given load path and query options; if a repeatable cache key cannot be generated, the query is "spoiled" so that it won't use caching. """ key = () if not cache_path: cache_path = effective_path if cache_path.path[0].is_aliased_class: # paths that are against an AliasedClass are unsafe to cache # with since the AliasedClass is an ad-hoc object. self.spoil(full=True) else: for opt in options: cache_key = opt._generate_cache_key(cache_path) if cache_key is False: self.spoil(full=True) elif cache_key is not None: key += cache_key self.add_criteria( lambda q: q._with_current_path( effective_path )._conditional_options(*options), cache_path.path, key, ) def _retrieve_baked_query(self, session): query = self._bakery.get(self._effective_key(session), None) if query is None: query = self._as_query(session) self._bakery[self._effective_key(session)] = query.with_session( None ) return query.with_session(session) def _bake(self, session): query = self._as_query(session) context = query._compile_context() self._bake_subquery_loaders(session, context) context.session = None context.query = query = context.query.with_session(None) query._execution_options = query._execution_options.union( {"compiled_cache": self._bakery} ) # we'll be holding onto the query for some of its state, # so delete some compilation-use-only attributes that can take up # space for attr in ( "_correlate", "_from_obj", "_mapper_adapter_map", "_joinpath", "_joinpoint", ): query.__dict__.pop(attr, None) # if the query is not safe to cache, we still do everything as though # we did cache it, since the receiver of _bake() assumes subqueryload # context was set up, etc. if context.query._bake_ok: self._bakery[self._effective_key(session)] = context return context def to_query(self, query_or_session): """Return the :class:`_query.Query` object for use as a subquery. This method should be used within the lambda callable being used to generate a step of an enclosing :class:`.BakedQuery`. The parameter should normally be the :class:`_query.Query` object that is passed to the lambda:: sub_bq = self.bakery(lambda s: s.query(User.name)) sub_bq += lambda q: q.filter( User.id == Address.user_id).correlate(Address) main_bq = self.bakery(lambda s: s.query(Address)) main_bq += lambda q: q.filter( sub_bq.to_query(q).exists()) In the case where the subquery is used in the first callable against a :class:`.Session`, the :class:`.Session` is also accepted:: sub_bq = self.bakery(lambda s: s.query(User.name)) sub_bq += lambda q: q.filter( User.id == Address.user_id).correlate(Address) main_bq = self.bakery( lambda s: s.query(Address.id, sub_bq.to_query(q).as_scalar()) ) :param query_or_session: a :class:`_query.Query` object or a class :class:`.Session` object, that is assumed to be within the context of an enclosing :class:`.BakedQuery` callable. .. versionadded:: 1.3 """ if isinstance(query_or_session, Session): session = query_or_session elif isinstance(query_or_session, Query): session = query_or_session.session if session is None: raise sa_exc.ArgumentError( "Given Query needs to be associated with a Session" ) else: raise TypeError( "Query or Session object expected, got %r." % type(query_or_session) ) return self._as_query(session) def _as_query(self, session): query = self.steps[0](session) for step in self.steps[1:]: query = step(query) return query def _bake_subquery_loaders(self, session, context): """convert subquery eager loaders in the cache into baked queries. For subquery eager loading to work, all we need here is that the Query point to the correct session when it is run. However, since we are "baking" anyway, we may as well also turn the query into a "baked" query so that we save on performance too. """ context.attributes["baked_queries"] = baked_queries = [] for k, v in list(context.attributes.items()): if isinstance(v, Query): if "subquery" in k: bk = BakedQuery(self._bakery, lambda *args: v) bk._cache_key = self._cache_key + k bk._bake(session) baked_queries.append((k, bk._cache_key, v)) del context.attributes[k] def _unbake_subquery_loaders( self, session, context, params, post_criteria ): """Retrieve subquery eager loaders stored by _bake_subquery_loaders and turn them back into Result objects that will iterate just like a Query object. """ if "baked_queries" not in context.attributes: return for k, cache_key, query in context.attributes["baked_queries"]: bk = BakedQuery( self._bakery, lambda sess, q=query: q.with_session(sess) ) bk._cache_key = cache_key q = bk.for_session(session) for fn in post_criteria: q = q.with_post_criteria(fn) context.attributes[k] = q.params(**params) class Result(object): """Invokes a :class:`.BakedQuery` against a :class:`.Session`. The :class:`.Result` object is where the actual :class:`.query.Query` object gets created, or retrieved from the cache, against a target :class:`.Session`, and is then invoked for results. """ __slots__ = "bq", "session", "_params", "_post_criteria" def __init__(self, bq, session): self.bq = bq self.session = session self._params = {} self._post_criteria = [] def params(self, *args, **kw): """Specify parameters to be replaced into the string SQL statement.""" if len(args) == 1: kw.update(args[0]) elif len(args) > 0: raise sa_exc.ArgumentError( "params() takes zero or one positional argument, " "which is a dictionary." ) self._params.update(kw) return self def _using_post_criteria(self, fns): if fns: self._post_criteria.extend(fns) return self def with_post_criteria(self, fn): """Add a criteria function that will be applied post-cache. This adds a function that will be run against the :class:`_query.Query` object after it is retrieved from the cache. Functions here can be used to alter the query in ways that **do not affect the SQL output**, such as execution options and shard identifiers (when using a shard-enabled query object) .. warning:: :meth:`.Result.with_post_criteria` functions are applied to the :class:`_query.Query` object **after** the query's SQL statement object has been retrieved from the cache. Any operations here which intend to modify the SQL should ensure that :meth:`.BakedQuery.spoil` was called first. .. versionadded:: 1.2 """ return self._using_post_criteria([fn]) def _as_query(self): q = self.bq._as_query(self.session).params(self._params) for fn in self._post_criteria: q = fn(q) return q def __str__(self): return str(self._as_query()) def __iter__(self): bq = self.bq if not self.session.enable_baked_queries or bq._spoiled: return iter(self._as_query()) baked_context = bq._bakery.get(bq._effective_key(self.session), None) if baked_context is None: baked_context = bq._bake(self.session) context = copy.copy(baked_context) context.session = self.session context.attributes = context.attributes.copy() bq._unbake_subquery_loaders( self.session, context, self._params, self._post_criteria ) context.statement.use_labels = True if context.autoflush and not context.populate_existing: self.session._autoflush() q = context.query.params(self._params).with_session(self.session) for fn in self._post_criteria: q = fn(q) return q._execute_and_instances(context) def count(self): """return the 'count'. Equivalent to :meth:`_query.Query.count`. Note this uses a subquery to ensure an accurate count regardless of the structure of the original statement. .. versionadded:: 1.1.6 """ col = func.count(literal_column("*")) bq = self.bq.with_criteria(lambda q: q.from_self(col)) return bq.for_session(self.session).params(self._params).scalar() def scalar(self): """Return the first element of the first result or None if no rows present. If multiple rows are returned, raises MultipleResultsFound. Equivalent to :meth:`_query.Query.scalar`. .. versionadded:: 1.1.6 """ try: ret = self.one() if not isinstance(ret, tuple): return ret return ret[0] except orm_exc.NoResultFound: return None def first(self): """Return the first row. Equivalent to :meth:`_query.Query.first`. """ bq = self.bq.with_criteria(lambda q: q.slice(0, 1)) ret = list( bq.for_session(self.session) .params(self._params) ._using_post_criteria(self._post_criteria) ) if len(ret) > 0: return ret[0] else: return None def one(self): """Return exactly one result or raise an exception. Equivalent to :meth:`_query.Query.one`. """ try: ret = self.one_or_none() except orm_exc.MultipleResultsFound as err: util.raise_( orm_exc.MultipleResultsFound( "Multiple rows were found for one()" ), replace_context=err, ) else: if ret is None: raise orm_exc.NoResultFound("No row was found for one()") return ret def one_or_none(self): """Return one or zero results, or raise an exception for multiple rows. Equivalent to :meth:`_query.Query.one_or_none`. .. versionadded:: 1.0.9 """ ret = list(self) l = len(ret) if l == 1: return ret[0] elif l == 0: return None else: raise orm_exc.MultipleResultsFound( "Multiple rows were found for one_or_none()" ) def all(self): """Return all rows. Equivalent to :meth:`_query.Query.all`. """ return list(self) def get(self, ident): """Retrieve an object based on identity. Equivalent to :meth:`_query.Query.get`. """ query = self.bq.steps[0](self.session) return query._get_impl(ident, self._load_on_pk_identity) def _load_on_pk_identity(self, query, primary_key_identity): """Load the given primary key identity from the database.""" mapper = query._mapper_zero() _get_clause, _get_params = mapper._get_clause def setup(query): _lcl_get_clause = _get_clause q = query._clone() q._get_condition() q._order_by = None # None present in ident - turn those comparisons # into "IS NULL" if None in primary_key_identity: nones = set( [ _get_params[col].key for col, value in zip( mapper.primary_key, primary_key_identity ) if value is None ] ) _lcl_get_clause = sql_util.adapt_criterion_to_null( _lcl_get_clause, nones ) _lcl_get_clause = q._adapt_clause(_lcl_get_clause, True, False) q._criterion = _lcl_get_clause for fn in self._post_criteria: q = fn(q) return q # cache the query against a key that includes # which positions in the primary key are NULL # (remember, we can map to an OUTER JOIN) bq = self.bq # add the clause we got from mapper._get_clause to the cache # key so that if a race causes multiple calls to _get_clause, # we've cached on ours bq = bq._clone() bq._cache_key += (_get_clause,) bq = bq.with_criteria( setup, tuple(elem is None for elem in primary_key_identity) ) params = dict( [ (_get_params[primary_key].key, id_val) for id_val, primary_key in zip( primary_key_identity, mapper.primary_key ) ] ) result = list(bq.for_session(self.session).params(**params)) l = len(result) if l > 1: raise orm_exc.MultipleResultsFound() elif l: return result[0] else: return None @util.deprecated( "1.2", "Baked lazy loading is now the default implementation." ) def bake_lazy_loaders(): """Enable the use of baked queries for all lazyloaders systemwide. The "baked" implementation of lazy loading is now the sole implementation for the base lazy loader; this method has no effect except for a warning. """ pass @util.deprecated( "1.2", "Baked lazy loading is now the default implementation." ) def unbake_lazy_loaders(): """Disable the use of baked queries for all lazyloaders systemwide. This method now raises NotImplementedError() as the "baked" implementation is the only lazy load implementation. The :paramref:`_orm.relationship.bake_queries` flag may be used to disable the caching of queries on a per-relationship basis. """ raise NotImplementedError( "Baked lazy loading is now the default implementation" ) @strategy_options.loader_option() def baked_lazyload(loadopt, attr): """Indicate that the given attribute should be loaded using "lazy" loading with a "baked" query used in the load. """ return loadopt.set_relationship_strategy(attr, {"lazy": "baked_select"}) @baked_lazyload._add_unbound_fn @util.deprecated( "1.2", "Baked lazy loading is now the default " "implementation for lazy loading.", ) def baked_lazyload(*keys): return strategy_options._UnboundLoad._from_keys( strategy_options._UnboundLoad.baked_lazyload, keys, False, {} ) @baked_lazyload._add_unbound_all_fn @util.deprecated( "1.2", "Baked lazy loading is now the default " "implementation for lazy loading.", ) def baked_lazyload_all(*keys): return strategy_options._UnboundLoad._from_keys( strategy_options._UnboundLoad.baked_lazyload, keys, True, {} ) baked_lazyload = baked_lazyload._unbound_fn baked_lazyload_all = baked_lazyload_all._unbound_all_fn bakery = BakedQuery.bakery
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