1. Mike Bayer
  2. sqlalchemy

Source

sqlalchemy / lib / sqlalchemy / sql / util.py

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# sql/util.py
# Copyright (C) 2005-2013 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

"""High level utilities which build upon other modules here.

"""

from .. import exc, util
from .base import _from_objects, ColumnSet
from . import operators, visitors
from itertools import chain
from collections import deque

from .elements import BindParameter, ColumnClause, ColumnElement, \
            Null, UnaryExpression, literal_column, Label
from .selectable import ScalarSelect, Join, FromClause, FromGrouping
from .schema import Column

join_condition = util.langhelpers.public_factory(
                            Join._join_condition,
                            ".sql.util.join_condition")

# names that are still being imported from the outside
from .annotation import _shallow_annotate, _deep_annotate, _deep_deannotate
from .elements import _find_columns
from .ddl import sort_tables


def find_join_source(clauses, join_to):
    """Given a list of FROM clauses and a selectable,
    return the first index and element from the list of
    clauses which can be joined against the selectable.  returns
    None, None if no match is found.

    e.g.::

        clause1 = table1.join(table2)
        clause2 = table4.join(table5)

        join_to = table2.join(table3)

        find_join_source([clause1, clause2], join_to) == clause1

    """

    selectables = list(_from_objects(join_to))
    for i, f in enumerate(clauses):
        for s in selectables:
            if f.is_derived_from(s):
                return i, f
    else:
        return None, None


def visit_binary_product(fn, expr):
    """Produce a traversal of the given expression, delivering
    column comparisons to the given function.

    The function is of the form::

        def my_fn(binary, left, right)

    For each binary expression located which has a
    comparison operator, the product of "left" and
    "right" will be delivered to that function,
    in terms of that binary.

    Hence an expression like::

        and_(
            (a + b) == q + func.sum(e + f),
            j == r
        )

    would have the traversal::

        a <eq> q
        a <eq> e
        a <eq> f
        b <eq> q
        b <eq> e
        b <eq> f
        j <eq> r

    That is, every combination of "left" and
    "right" that doesn't further contain
    a binary comparison is passed as pairs.

    """
    stack = []

    def visit(element):
        if isinstance(element, ScalarSelect):
            # we dont want to dig into correlated subqueries,
            # those are just column elements by themselves
            yield element
        elif element.__visit_name__ == 'binary' and \
            operators.is_comparison(element.operator):
            stack.insert(0, element)
            for l in visit(element.left):
                for r in visit(element.right):
                    fn(stack[0], l, r)
            stack.pop(0)
            for elem in element.get_children():
                visit(elem)
        else:
            if isinstance(element, ColumnClause):
                yield element
            for elem in element.get_children():
                for e in visit(elem):
                    yield e
    list(visit(expr))


def find_tables(clause, check_columns=False,
                include_aliases=False, include_joins=False,
                include_selects=False, include_crud=False):
    """locate Table objects within the given expression."""

    tables = []
    _visitors = {}

    if include_selects:
        _visitors['select'] = _visitors['compound_select'] = tables.append

    if include_joins:
        _visitors['join'] = tables.append

    if include_aliases:
        _visitors['alias'] = tables.append

    if include_crud:
        _visitors['insert'] = _visitors['update'] = \
                    _visitors['delete'] = lambda ent: tables.append(ent.table)

    if check_columns:
        def visit_column(column):
            tables.append(column.table)
        _visitors['column'] = visit_column

    _visitors['table'] = tables.append

    visitors.traverse(clause, {'column_collections': False}, _visitors)
    return tables



def unwrap_order_by(clause):
    """Break up an 'order by' expression into individual column-expressions,
    without DESC/ASC/NULLS FIRST/NULLS LAST"""

    cols = util.column_set()
    stack = deque([clause])
    while stack:
        t = stack.popleft()
        if isinstance(t, ColumnElement) and \
            (
                not isinstance(t, UnaryExpression) or \
                not operators.is_ordering_modifier(t.modifier)
            ):
            cols.add(t)
        else:
            for c in t.get_children():
                stack.append(c)
    return cols


def clause_is_present(clause, search):
    """Given a target clause and a second to search within, return True
    if the target is plainly present in the search without any
    subqueries or aliases involved.

    Basically descends through Joins.

    """

    for elem in surface_selectables(search):
        if clause == elem:  # use == here so that Annotated's compare
            return True
    else:
        return False

def surface_selectables(clause):
    stack = [clause]
    while stack:
        elem = stack.pop()
        yield elem
        if isinstance(elem, Join):
            stack.extend((elem.left, elem.right))
        elif isinstance(elem, FromGrouping):
            stack.append(elem.element)

def selectables_overlap(left, right):
    """Return True if left/right have some overlapping selectable"""

    return bool(
                set(surface_selectables(left)).intersection(
                        surface_selectables(right)
                    )
            )

def bind_values(clause):
    """Return an ordered list of "bound" values in the given clause.

    E.g.::

        >>> expr = and_(
        ...    table.c.foo==5, table.c.foo==7
        ... )
        >>> bind_values(expr)
        [5, 7]
    """

    v = []

    def visit_bindparam(bind):
        v.append(bind.effective_value)

    visitors.traverse(clause, {}, {'bindparam': visit_bindparam})
    return v


def _quote_ddl_expr(element):
    if isinstance(element, util.string_types):
        element = element.replace("'", "''")
        return "'%s'" % element
    else:
        return repr(element)


class _repr_params(object):
    """A string view of bound parameters, truncating
    display to the given number of 'multi' parameter sets.

    """
    def __init__(self, params, batches):
        self.params = params
        self.batches = batches

    def __repr__(self):
        if isinstance(self.params, (list, tuple)) and \
            len(self.params) > self.batches and \
            isinstance(self.params[0], (list, dict, tuple)):
            msg = " ... displaying %i of %i total bound parameter sets ... "
            return ' '.join((
                        repr(self.params[:self.batches - 2])[0:-1],
                        msg % (self.batches, len(self.params)),
                        repr(self.params[-2:])[1:]
                    ))
        else:
            return repr(self.params)


def expression_as_ddl(clause):
    """Given a SQL expression, convert for usage in DDL, such as
     CREATE INDEX and CHECK CONSTRAINT.

     Converts bind params into quoted literals, column identifiers
     into detached column constructs so that the parent table
     identifier is not included.

    """
    def repl(element):
        if isinstance(element, BindParameter):
            return literal_column(_quote_ddl_expr(element.value))
        elif isinstance(element, ColumnClause) and \
                element.table is not None:
            col = ColumnClause(element.name)
            return col
        else:
            return None

    return visitors.replacement_traverse(clause, {}, repl)


def adapt_criterion_to_null(crit, nulls):
    """given criterion containing bind params, convert selected elements
    to IS NULL.

    """

    def visit_binary(binary):
        if isinstance(binary.left, BindParameter) \
            and binary.left._identifying_key in nulls:
            # reverse order if the NULL is on the left side
            binary.left = binary.right
            binary.right = Null()
            binary.operator = operators.is_
            binary.negate = operators.isnot
        elif isinstance(binary.right, BindParameter) \
            and binary.right._identifying_key in nulls:
            binary.right = Null()
            binary.operator = operators.is_
            binary.negate = operators.isnot

    return visitors.cloned_traverse(crit, {}, {'binary': visit_binary})


def splice_joins(left, right, stop_on=None):
    if left is None:
        return right

    stack = [(right, None)]

    adapter = ClauseAdapter(left)
    ret = None
    while stack:
        (right, prevright) = stack.pop()
        if isinstance(right, Join) and right is not stop_on:
            right = right._clone()
            right._reset_exported()
            right.onclause = adapter.traverse(right.onclause)
            stack.append((right.left, right))
        else:
            right = adapter.traverse(right)
        if prevright is not None:
            prevright.left = right
        if ret is None:
            ret = right

    return ret


def reduce_columns(columns, *clauses, **kw):
    """given a list of columns, return a 'reduced' set based on natural
    equivalents.

    the set is reduced to the smallest list of columns which have no natural
    equivalent present in the list.  A "natural equivalent" means that two
    columns will ultimately represent the same value because they are related
    by a foreign key.

    \*clauses is an optional list of join clauses which will be traversed
    to further identify columns that are "equivalent".

    \**kw may specify 'ignore_nonexistent_tables' to ignore foreign keys
    whose tables are not yet configured, or columns that aren't yet present.

    This function is primarily used to determine the most minimal "primary key"
    from a selectable, by reducing the set of primary key columns present
    in the the selectable to just those that are not repeated.

    """
    ignore_nonexistent_tables = kw.pop('ignore_nonexistent_tables', False)
    only_synonyms = kw.pop('only_synonyms', False)

    columns = util.ordered_column_set(columns)

    omit = util.column_set()
    for col in columns:
        for fk in chain(*[c.foreign_keys for c in col.proxy_set]):
            for c in columns:
                if c is col:
                    continue
                try:
                    fk_col = fk.column
                except exc.NoReferencedColumnError:
                    # TODO: add specific coverage here
                    # to test/sql/test_selectable ReduceTest
                    if ignore_nonexistent_tables:
                        continue
                    else:
                        raise
                except exc.NoReferencedTableError:
                    # TODO: add specific coverage here
                    # to test/sql/test_selectable ReduceTest
                    if ignore_nonexistent_tables:
                        continue
                    else:
                        raise
                if fk_col.shares_lineage(c) and \
                    (not only_synonyms or \
                    c.name == col.name):
                    omit.add(col)
                    break

    if clauses:
        def visit_binary(binary):
            if binary.operator == operators.eq:
                cols = util.column_set(chain(*[c.proxy_set
                            for c in columns.difference(omit)]))
                if binary.left in cols and binary.right in cols:
                    for c in reversed(columns):
                        if c.shares_lineage(binary.right) and \
                            (not only_synonyms or \
                            c.name == binary.left.name):
                            omit.add(c)
                            break
        for clause in clauses:
            if clause is not None:
                visitors.traverse(clause, {}, {'binary': visit_binary})

    return ColumnSet(columns.difference(omit))


def criterion_as_pairs(expression, consider_as_foreign_keys=None,
                        consider_as_referenced_keys=None, any_operator=False):
    """traverse an expression and locate binary criterion pairs."""

    if consider_as_foreign_keys and consider_as_referenced_keys:
        raise exc.ArgumentError("Can only specify one of "
                                "'consider_as_foreign_keys' or "
                                "'consider_as_referenced_keys'")

    def col_is(a, b):
        #return a is b
        return a.compare(b)

    def visit_binary(binary):
        if not any_operator and binary.operator is not operators.eq:
            return
        if not isinstance(binary.left, ColumnElement) or \
                    not isinstance(binary.right, ColumnElement):
            return

        if consider_as_foreign_keys:
            if binary.left in consider_as_foreign_keys and \
                        (col_is(binary.right, binary.left) or
                        binary.right not in consider_as_foreign_keys):
                pairs.append((binary.right, binary.left))
            elif binary.right in consider_as_foreign_keys and \
                        (col_is(binary.left, binary.right) or
                        binary.left not in consider_as_foreign_keys):
                pairs.append((binary.left, binary.right))
        elif consider_as_referenced_keys:
            if binary.left in consider_as_referenced_keys and \
                        (col_is(binary.right, binary.left) or
                        binary.right not in consider_as_referenced_keys):
                pairs.append((binary.left, binary.right))
            elif binary.right in consider_as_referenced_keys and \
                        (col_is(binary.left, binary.right) or
                        binary.left not in consider_as_referenced_keys):
                pairs.append((binary.right, binary.left))
        else:
            if isinstance(binary.left, Column) and \
                        isinstance(binary.right, Column):
                if binary.left.references(binary.right):
                    pairs.append((binary.right, binary.left))
                elif binary.right.references(binary.left):
                    pairs.append((binary.left, binary.right))
    pairs = []
    visitors.traverse(expression, {}, {'binary': visit_binary})
    return pairs



class AliasedRow(object):
    """Wrap a RowProxy with a translation map.

    This object allows a set of keys to be translated
    to those present in a RowProxy.

    """
    def __init__(self, row, map):
        # AliasedRow objects don't nest, so un-nest
        # if another AliasedRow was passed
        if isinstance(row, AliasedRow):
            self.row = row.row
        else:
            self.row = row
        self.map = map

    def __contains__(self, key):
        return self.map[key] in self.row

    def has_key(self, key):
        return key in self

    def __getitem__(self, key):
        return self.row[self.map[key]]

    def keys(self):
        return self.row.keys()


class ClauseAdapter(visitors.ReplacingCloningVisitor):
    """Clones and modifies clauses based on column correspondence.

    E.g.::

      table1 = Table('sometable', metadata,
          Column('col1', Integer),
          Column('col2', Integer)
          )
      table2 = Table('someothertable', metadata,
          Column('col1', Integer),
          Column('col2', Integer)
          )

      condition = table1.c.col1 == table2.c.col1

    make an alias of table1::

      s = table1.alias('foo')

    calling ``ClauseAdapter(s).traverse(condition)`` converts
    condition to read::

      s.c.col1 == table2.c.col1

    """
    def __init__(self, selectable, equivalents=None,
                        include=None, exclude=None,
                        include_fn=None, exclude_fn=None,
                        adapt_on_names=False):
        self.__traverse_options__ = {'stop_on': [selectable]}
        self.selectable = selectable
        if include:
            assert not include_fn
            self.include_fn = lambda e: e in include
        else:
            self.include_fn = include_fn
        if exclude:
            assert not exclude_fn
            self.exclude_fn = lambda e: e in exclude
        else:
            self.exclude_fn = exclude_fn
        self.equivalents = util.column_dict(equivalents or {})
        self.adapt_on_names = adapt_on_names

    def _corresponding_column(self, col, require_embedded,
                              _seen=util.EMPTY_SET):
        newcol = self.selectable.corresponding_column(
                                    col,
                                    require_embedded=require_embedded)
        if newcol is None and col in self.equivalents and col not in _seen:
            for equiv in self.equivalents[col]:
                newcol = self._corresponding_column(equiv,
                                require_embedded=require_embedded,
                                _seen=_seen.union([col]))
                if newcol is not None:
                    return newcol
        if self.adapt_on_names and newcol is None:
            newcol = self.selectable.c.get(col.name)
        return newcol

    magic_flag = False
    def replace(self, col):
        if not self.magic_flag and isinstance(col, FromClause) and \
            self.selectable.is_derived_from(col):
            return self.selectable
        elif not isinstance(col, ColumnElement):
            return None
        elif self.include_fn and not self.include_fn(col):
            return None
        elif self.exclude_fn and self.exclude_fn(col):
            return None
        else:
            return self._corresponding_column(col, True)


class ColumnAdapter(ClauseAdapter):
    """Extends ClauseAdapter with extra utility functions.

    Provides the ability to "wrap" this ClauseAdapter
    around another, a columns dictionary which returns
    adapted elements given an original, and an
    adapted_row() factory.

    """
    def __init__(self, selectable, equivalents=None,
                        chain_to=None, include=None,
                        exclude=None, adapt_required=False):
        ClauseAdapter.__init__(self, selectable, equivalents, include, exclude)
        if chain_to:
            self.chain(chain_to)
        self.columns = util.populate_column_dict(self._locate_col)
        self.adapt_required = adapt_required

    def wrap(self, adapter):
        ac = self.__class__.__new__(self.__class__)
        ac.__dict__ = self.__dict__.copy()
        ac._locate_col = ac._wrap(ac._locate_col, adapter._locate_col)
        ac.adapt_clause = ac._wrap(ac.adapt_clause, adapter.adapt_clause)
        ac.adapt_list = ac._wrap(ac.adapt_list, adapter.adapt_list)
        ac.columns = util.populate_column_dict(ac._locate_col)
        return ac

    adapt_clause = ClauseAdapter.traverse
    adapt_list = ClauseAdapter.copy_and_process

    def _wrap(self, local, wrapped):
        def locate(col):
            col = local(col)
            return wrapped(col)
        return locate

    def _locate_col(self, col):
        c = self._corresponding_column(col, True)
        if c is None:
            c = self.adapt_clause(col)

            # anonymize labels in case they have a hardcoded name
            if isinstance(c, Label):
                c = c.label(None)

        # adapt_required used by eager loading to indicate that
        # we don't trust a result row column that is not translated.
        # this is to prevent a column from being interpreted as that
        # of the child row in a self-referential scenario, see
        # inheritance/test_basic.py->EagerTargetingTest.test_adapt_stringency
        if self.adapt_required and c is col:
            return None

        return c

    def adapted_row(self, row):
        return AliasedRow(row, self.columns)

    def __getstate__(self):
        d = self.__dict__.copy()
        del d['columns']
        return d

    def __setstate__(self, state):
        self.__dict__.update(state)
        self.columns = util.PopulateDict(self._locate_col)