path: root/lib/sqlalchemy/ext/baked.py

# sqlalchemy/ext/baked.py
# Copyright (C) 2005-2015 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.


"""

from ..orm.query import Query
from ..orm import strategies, attributes, properties, \
    strategy_options, util as orm_util, interfaces
from .. import log as sqla_log
from ..sql import util as sql_util
from ..orm import exc as orm_exc
from .. import exc as sa_exc
from .. import util

import copy
import logging

log = logging.getLogger(__name__)


class BakedQuery(object):
    """A builder object for :class:`.query.Query` objects."""

    __slots__ = 'steps', '_bakery', '_cache_key', '_spoiled'

    def __init__(self, bakery, initial_fn, args=()):
        if args:
            self._cache_key = tuple(args)
        else:
            self._cache_key = ()
        self._update_cache_key(initial_fn)
        self.steps = [initial_fn]
        self._spoiled = False
        self._bakery = bakery

    @classmethod
    def bakery(cls, size=200):
        """Construct a new bakery."""

        _bakery = util.LRUCache(size)

        def call(initial_fn):
            return cls(_bakery, initial_fn)

        return call

    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` object is built from scratch each
         time, with all creational functions being called on each
         invocation.

        """
        if not full:
            _spoil_point = self._clone()
            _spoil_point._cache_key += ('_query_only', )
            self.steps = [_spoil_point._retrieve_baked_query]
        self._spoiled = True
        return self

    def _retrieve_baked_query(self, session):
        query = self._bakery.get(self._cache_key, None)
        if query is None:
            query = self._as_query(session)
            self._bakery[self._cache_key] = 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)
        self._bakery[self._cache_key] = context
        return context

    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):
        """Retrieve subquery eager loaders stored by _bake_subquery_loaders
        and turn them back into Result objects that will iterate just
        like a Query object.

        """
        for k, cache_key, query in context.attributes["baked_queries"]:
            bk = BakedQuery(self._bakery, lambda sess: query.with_session(sess))
            bk._cache_key = cache_key
            context.attributes[k] = bk.for_session(session).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'

    def __init__(self, bq, session):
        self.bq = bq
        self.session = session
        self._params = {}

    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 _as_query(self):
        return self.bq._as_query(self.session).params(self._params)

    def __str__(self):
        return str(self._as_query())

    def __iter__(self):
        bq = self.bq
        if bq._spoiled:
            return iter(self._as_query())

        baked_context = bq._bakery.get(bq._cache_key, 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)

        context.statement.use_labels = True
        if context.autoflush and not context.populate_existing:
            self.session._autoflush()
        return context.query.params(self._params).\
            with_session(self.session)._execute_and_instances(context)

    def first(self):
        """Return the first row.

        Equivalent to :meth:`.Query.first`.

        """
        bq = self.bq.with_criteria(lambda q: q.slice(0, 1))
        ret = list(bq.for_session(self.session).params(self._params))
        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.one`.

        """
        ret = list(self)

        l = len(ret)
        if l == 1:
            return ret[0]
        elif l == 0:
            raise orm_exc.NoResultFound("No row was found for one()")
        else:
            raise orm_exc.MultipleResultsFound(
                "Multiple rows were found for one()")

    def all(self):
        """Return all rows.

        Equivalent to :meth:`.Query.all`.

        """
        return list(self)

    def get(self, ident):
        """Retrieve an object based on identity.

        Equivalent to :meth:`.Query.get`.

        """

        query = self.bq.steps[0](self.session)
        return query._get_impl(ident, self._load_on_ident)

    def _load_on_ident(self, query, key):
        """Load the given identity key from the database."""

        ident = key[1]

        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 ident:
                nones = set([
                    _get_params[col].key for col, value in
                    zip(mapper.primary_key, ident) 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
            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

        bq = bq.with_criteria(setup, tuple(elem is None for elem in ident))

        params = dict([
            (_get_params[primary_key].key, id_val)
            for id_val, primary_key in zip(ident, 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


def bake_lazy_loaders():
    """Enable the use of baked queries for all lazyloaders systemwide.

    This operation should be safe for all lazy loaders, and will reduce
    Python overhead for these operations.

    """
    strategies.LazyLoader._strategy_keys[:] = []
    BakedLazyLoader._strategy_keys[:] = []

    properties.RelationshipProperty.strategy_for(
        lazy="select")(BakedLazyLoader)
    properties.RelationshipProperty.strategy_for(
        lazy=True)(BakedLazyLoader)
    properties.RelationshipProperty.strategy_for(
        lazy="baked_select")(BakedLazyLoader)


def unbake_lazy_loaders():
    """Disable the use of baked queries for all lazyloaders systemwide.

    This operation reverts the changes produced by :func:`.bake_lazy_loaders`.

    """
    strategies.LazyLoader._strategy_keys[:] = []
    BakedLazyLoader._strategy_keys[:] = []

    properties.RelationshipProperty.strategy_for(
        lazy="select")(strategies.LazyLoader)
    properties.RelationshipProperty.strategy_for(
        lazy=True)(strategies.LazyLoader)
    properties.RelationshipProperty.strategy_for(
        lazy="baked_select")(BakedLazyLoader)
    assert strategies.LazyLoader._strategy_keys


@sqla_log.class_logger
@properties.RelationshipProperty.strategy_for(lazy="baked_select")
class BakedLazyLoader(strategies.LazyLoader):

    def _emit_lazyload(self, session, state, ident_key, passive):
        q = BakedQuery(
            self.mapper._compiled_cache,
            lambda session: session.query(self.mapper))
        q.add_criteria(
            lambda q: q._adapt_all_clauses()._with_invoke_all_eagers(False),
            self.parent_property)

        if not self.parent_property.bake_queries:
            q.spoil(full=True)

        if self.parent_property.secondary is not None:
            q.add_criteria(
                lambda q:
                q.select_from(self.mapper, self.parent_property.secondary))

        pending = not state.key

        # don't autoflush on pending
        if pending or passive & attributes.NO_AUTOFLUSH:
            q.add_criteria(lambda q: q.autoflush(False))

        if state.load_path:
            q.spoil()
            q.add_criteria(
                lambda q:
                q._with_current_path(state.load_path[self.parent_property]))

        if state.load_options:
            q.spoil()
            q.add_criteria(
                lambda q: q._conditional_options(*state.load_options))

        if self.use_get:
            return q(session)._load_on_ident(
                session.query(self.mapper), ident_key)

        if self.parent_property.order_by:
            q.add_criteria(
                lambda q:
                q.order_by(*util.to_list(self.parent_property.order_by)))

        for rev in self.parent_property._reverse_property:
            # reverse props that are MANYTOONE are loading *this*
            # object from get(), so don't need to eager out to those.
            if rev.direction is interfaces.MANYTOONE and \
                rev._use_get and \
                    not isinstance(rev.strategy, strategies.LazyLoader):
                q.add_criteria(
                    lambda q:
                    q.options(
                        strategy_options.Load(
                            rev.parent).baked_lazyload(rev.key)))

        lazy_clause, params = self._generate_lazy_clause(state, passive)

        if pending:
            if orm_util._none_set.intersection(params.values()):
                return None

        q.add_criteria(lambda q: q.filter(lazy_clause))
        result = q(session).params(**params).all()
        if self.uselist:
            return result
        else:
            l = len(result)
            if l:
                if l > 1:
                    util.warn(
                        "Multiple rows returned with "
                        "uselist=False for lazily-loaded attribute '%s' "
                        % self.parent_property)

                return result[0]
            else:
                return None


@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
def baked_lazyload(*keys):
    return strategy_options._UnboundLoad._from_keys(
        strategy_options._UnboundLoad.baked_lazyload, keys, False, {})


@baked_lazyload._add_unbound_all_fn
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