django1/django/db/models/expressions.py

956 lines
33 KiB
Python

import copy
import datetime
from django.conf import settings
from django.core.exceptions import FieldError
from django.db.backends import utils as backend_utils
from django.db.models import fields
from django.db.models.constants import LOOKUP_SEP
from django.db.models.query_utils import Q, refs_aggregate
from django.utils import six, timezone
from django.utils.functional import cached_property
class Combinable(object):
"""
Provides the ability to combine one or two objects with
some connector. For example F('foo') + F('bar').
"""
# Arithmetic connectors
ADD = '+'
SUB = '-'
MUL = '*'
DIV = '/'
POW = '^'
# The following is a quoted % operator - it is quoted because it can be
# used in strings that also have parameter substitution.
MOD = '%%'
# Bitwise operators - note that these are generated by .bitand()
# and .bitor(), the '&' and '|' are reserved for boolean operator
# usage.
BITAND = '&'
BITOR = '|'
def _combine(self, other, connector, reversed, node=None):
if not hasattr(other, 'resolve_expression'):
# everything must be resolvable to an expression
if isinstance(other, datetime.timedelta):
other = DurationValue(other, output_field=fields.DurationField())
else:
other = Value(other)
if reversed:
return CombinedExpression(other, connector, self)
return CombinedExpression(self, connector, other)
#############
# OPERATORS #
#############
def __add__(self, other):
return self._combine(other, self.ADD, False)
def __sub__(self, other):
return self._combine(other, self.SUB, False)
def __mul__(self, other):
return self._combine(other, self.MUL, False)
def __truediv__(self, other):
return self._combine(other, self.DIV, False)
def __div__(self, other): # Python 2 compatibility
return type(self).__truediv__(self, other)
def __mod__(self, other):
return self._combine(other, self.MOD, False)
def __pow__(self, other):
return self._combine(other, self.POW, False)
def __and__(self, other):
raise NotImplementedError(
"Use .bitand() and .bitor() for bitwise logical operations."
)
def bitand(self, other):
return self._combine(other, self.BITAND, False)
def __or__(self, other):
raise NotImplementedError(
"Use .bitand() and .bitor() for bitwise logical operations."
)
def bitor(self, other):
return self._combine(other, self.BITOR, False)
def __radd__(self, other):
return self._combine(other, self.ADD, True)
def __rsub__(self, other):
return self._combine(other, self.SUB, True)
def __rmul__(self, other):
return self._combine(other, self.MUL, True)
def __rtruediv__(self, other):
return self._combine(other, self.DIV, True)
def __rdiv__(self, other): # Python 2 compatibility
return type(self).__rtruediv__(self, other)
def __rmod__(self, other):
return self._combine(other, self.MOD, True)
def __rpow__(self, other):
return self._combine(other, self.POW, True)
def __rand__(self, other):
raise NotImplementedError(
"Use .bitand() and .bitor() for bitwise logical operations."
)
def __ror__(self, other):
raise NotImplementedError(
"Use .bitand() and .bitor() for bitwise logical operations."
)
class BaseExpression(object):
"""
Base class for all query expressions.
"""
# aggregate specific fields
is_summary = False
def __init__(self, output_field=None):
self._output_field = output_field
def get_db_converters(self, connection):
return [self.convert_value] + self.output_field.get_db_converters(connection)
def get_source_expressions(self):
return []
def set_source_expressions(self, exprs):
assert len(exprs) == 0
def _parse_expressions(self, *expressions):
return [
arg if hasattr(arg, 'resolve_expression') else (
F(arg) if isinstance(arg, six.string_types) else Value(arg)
) for arg in expressions
]
def as_sql(self, compiler, connection):
"""
Responsible for returning a (sql, [params]) tuple to be included
in the current query.
Different backends can provide their own implementation, by
providing an `as_{vendor}` method and patching the Expression:
```
def override_as_sql(self, compiler, connection):
# custom logic
return super(Expression, self).as_sql(compiler, connection)
setattr(Expression, 'as_' + connection.vendor, override_as_sql)
```
Arguments:
* compiler: the query compiler responsible for generating the query.
Must have a compile method, returning a (sql, [params]) tuple.
Calling compiler(value) will return a quoted `value`.
* connection: the database connection used for the current query.
Returns: (sql, params)
Where `sql` is a string containing ordered sql parameters to be
replaced with the elements of the list `params`.
"""
raise NotImplementedError("Subclasses must implement as_sql()")
@cached_property
def contains_aggregate(self):
for expr in self.get_source_expressions():
if expr and expr.contains_aggregate:
return True
return False
def resolve_expression(self, query=None, allow_joins=True, reuse=None, summarize=False, for_save=False):
"""
Provides the chance to do any preprocessing or validation before being
added to the query.
Arguments:
* query: the backend query implementation
* allow_joins: boolean allowing or denying use of joins
in this query
* reuse: a set of reusable joins for multijoins
* summarize: a terminal aggregate clause
* for_save: whether this expression about to be used in a save or update
Returns: an Expression to be added to the query.
"""
c = self.copy()
c.is_summary = summarize
c.set_source_expressions([
expr.resolve_expression(query, allow_joins, reuse, summarize)
for expr in c.get_source_expressions()
])
return c
def _prepare(self):
"""
Hook used by Field.get_prep_lookup() to do custom preparation.
"""
return self
@property
def field(self):
return self.output_field
@cached_property
def output_field(self):
"""
Returns the output type of this expressions.
"""
if self._output_field_or_none is None:
raise FieldError("Cannot resolve expression type, unknown output_field")
return self._output_field_or_none
@cached_property
def _output_field_or_none(self):
"""
Returns the output field of this expression, or None if no output type
can be resolved. Note that the 'output_field' property will raise
FieldError if no type can be resolved, but this attribute allows for
None values.
"""
if self._output_field is None:
self._resolve_output_field()
return self._output_field
def _resolve_output_field(self):
"""
Attempts to infer the output type of the expression. If the output
fields of all source fields match then we can simply infer the same
type here. This isn't always correct, but it makes sense most of the
time.
Consider the difference between `2 + 2` and `2 / 3`. Inferring
the type here is a convenience for the common case. The user should
supply their own output_field with more complex computations.
If a source does not have an `_output_field` then we exclude it from
this check. If all sources are `None`, then an error will be thrown
higher up the stack in the `output_field` property.
"""
if self._output_field is None:
sources = self.get_source_fields()
num_sources = len(sources)
if num_sources == 0:
self._output_field = None
else:
for source in sources:
if self._output_field is None:
self._output_field = source
if source is not None and not isinstance(self._output_field, source.__class__):
raise FieldError(
"Expression contains mixed types. You must set output_field")
def convert_value(self, value, expression, connection, context):
"""
Expressions provide their own converters because users have the option
of manually specifying the output_field which may be a different type
from the one the database returns.
"""
field = self.output_field
internal_type = field.get_internal_type()
if value is None:
return value
elif internal_type == 'FloatField':
return float(value)
elif internal_type.endswith('IntegerField'):
return int(value)
elif internal_type == 'DecimalField':
return backend_utils.typecast_decimal(value)
return value
def get_lookup(self, lookup):
return self.output_field.get_lookup(lookup)
def get_transform(self, name):
return self.output_field.get_transform(name)
def relabeled_clone(self, change_map):
clone = self.copy()
clone.set_source_expressions(
[e.relabeled_clone(change_map) for e in self.get_source_expressions()])
return clone
def copy(self):
c = copy.copy(self)
c.copied = True
return c
def refs_aggregate(self, existing_aggregates):
"""
Does this expression contain a reference to some of the
existing aggregates? If so, returns the aggregate and also
the lookup parts that *weren't* found. So, if
exsiting_aggregates = {'max_id': Max('id')}
self.name = 'max_id'
queryset.filter(max_id__range=[10,100])
then this method will return Max('id') and those parts of the
name that weren't found. In this case `max_id` is found and the range
portion is returned as ('range',).
"""
for node in self.get_source_expressions():
agg, lookup = node.refs_aggregate(existing_aggregates)
if agg:
return agg, lookup
return False, ()
def get_group_by_cols(self):
if not self.contains_aggregate:
return [self]
cols = []
for source in self.get_source_expressions():
cols.extend(source.get_group_by_cols())
return cols
def get_source_fields(self):
"""
Returns the underlying field types used by this
aggregate.
"""
return [e._output_field_or_none for e in self.get_source_expressions()]
def asc(self):
return OrderBy(self)
def desc(self):
return OrderBy(self, descending=True)
def reverse_ordering(self):
return self
class Expression(BaseExpression, Combinable):
"""
An expression that can be combined with other expressions.
"""
pass
class CombinedExpression(Expression):
def __init__(self, lhs, connector, rhs, output_field=None):
super(CombinedExpression, self).__init__(output_field=output_field)
self.connector = connector
self.lhs = lhs
self.rhs = rhs
def __repr__(self):
return "<{}: {}>".format(self.__class__.__name__, self)
def __str__(self):
return "{} {} {}".format(self.lhs, self.connector, self.rhs)
def get_source_expressions(self):
return [self.lhs, self.rhs]
def set_source_expressions(self, exprs):
self.lhs, self.rhs = exprs
def as_sql(self, compiler, connection):
try:
lhs_output = self.lhs.output_field
except FieldError:
lhs_output = None
try:
rhs_output = self.rhs.output_field
except FieldError:
rhs_output = None
if (not connection.features.has_native_duration_field and
((lhs_output and lhs_output.get_internal_type() == 'DurationField')
or (rhs_output and rhs_output.get_internal_type() == 'DurationField'))):
return DurationExpression(self.lhs, self.connector, self.rhs).as_sql(compiler, connection)
expressions = []
expression_params = []
sql, params = compiler.compile(self.lhs)
expressions.append(sql)
expression_params.extend(params)
sql, params = compiler.compile(self.rhs)
expressions.append(sql)
expression_params.extend(params)
# order of precedence
expression_wrapper = '(%s)'
sql = connection.ops.combine_expression(self.connector, expressions)
return expression_wrapper % sql, expression_params
def resolve_expression(self, query=None, allow_joins=True, reuse=None, summarize=False, for_save=False):
c = self.copy()
c.is_summary = summarize
c.lhs = c.lhs.resolve_expression(query, allow_joins, reuse, summarize, for_save)
c.rhs = c.rhs.resolve_expression(query, allow_joins, reuse, summarize, for_save)
return c
class DurationExpression(CombinedExpression):
def compile(self, side, compiler, connection):
if not isinstance(side, DurationValue):
try:
output = side.output_field
except FieldError:
pass
else:
if output.get_internal_type() == 'DurationField':
sql, params = compiler.compile(side)
return connection.ops.format_for_duration_arithmetic(sql), params
return compiler.compile(side)
def as_sql(self, compiler, connection):
connection.ops.check_expression_support(self)
expressions = []
expression_params = []
sql, params = self.compile(self.lhs, compiler, connection)
expressions.append(sql)
expression_params.extend(params)
sql, params = self.compile(self.rhs, compiler, connection)
expressions.append(sql)
expression_params.extend(params)
# order of precedence
expression_wrapper = '(%s)'
sql = connection.ops.combine_duration_expression(self.connector, expressions)
return expression_wrapper % sql, expression_params
class F(Combinable):
"""
An object capable of resolving references to existing query objects.
"""
def __init__(self, name):
"""
Arguments:
* name: the name of the field this expression references
"""
self.name = name
def __repr__(self):
return "{}({})".format(self.__class__.__name__, self.name)
def resolve_expression(self, query=None, allow_joins=True, reuse=None, summarize=False, for_save=False):
return query.resolve_ref(self.name, allow_joins, reuse, summarize)
def refs_aggregate(self, existing_aggregates):
return refs_aggregate(self.name.split(LOOKUP_SEP), existing_aggregates)
def asc(self):
return OrderBy(self)
def desc(self):
return OrderBy(self, descending=True)
class Func(Expression):
"""
A SQL function call.
"""
function = None
template = '%(function)s(%(expressions)s)'
arg_joiner = ', '
def __init__(self, *expressions, **extra):
output_field = extra.pop('output_field', None)
super(Func, self).__init__(output_field=output_field)
self.source_expressions = self._parse_expressions(*expressions)
self.extra = extra
def __repr__(self):
args = self.arg_joiner.join(str(arg) for arg in self.source_expressions)
extra = ', '.join(str(key) + '=' + str(val) for key, val in self.extra.items())
if extra:
return "{}({}, {})".format(self.__class__.__name__, args, extra)
return "{}({})".format(self.__class__.__name__, args)
def get_source_expressions(self):
return self.source_expressions
def set_source_expressions(self, exprs):
self.source_expressions = exprs
def resolve_expression(self, query=None, allow_joins=True, reuse=None, summarize=False, for_save=False):
c = self.copy()
c.is_summary = summarize
for pos, arg in enumerate(c.source_expressions):
c.source_expressions[pos] = arg.resolve_expression(query, allow_joins, reuse, summarize, for_save)
return c
def as_sql(self, compiler, connection, function=None, template=None):
connection.ops.check_expression_support(self)
sql_parts = []
params = []
for arg in self.source_expressions:
arg_sql, arg_params = compiler.compile(arg)
sql_parts.append(arg_sql)
params.extend(arg_params)
if function is None:
self.extra['function'] = self.extra.get('function', self.function)
else:
self.extra['function'] = function
self.extra['expressions'] = self.extra['field'] = self.arg_joiner.join(sql_parts)
template = template or self.extra.get('template', self.template)
return template % self.extra, params
def copy(self):
copy = super(Func, self).copy()
copy.source_expressions = self.source_expressions[:]
copy.extra = self.extra.copy()
return copy
class Value(Expression):
"""
Represents a wrapped value as a node within an expression
"""
def __init__(self, value, output_field=None):
"""
Arguments:
* value: the value this expression represents. The value will be
added into the sql parameter list and properly quoted.
* output_field: an instance of the model field type that this
expression will return, such as IntegerField() or CharField().
"""
super(Value, self).__init__(output_field=output_field)
self.value = value
def __repr__(self):
return "{}({})".format(self.__class__.__name__, self.value)
def as_sql(self, compiler, connection):
connection.ops.check_expression_support(self)
val = self.value
# check _output_field to avoid triggering an exception
if self._output_field is not None:
if self.for_save:
val = self.output_field.get_db_prep_save(val, connection=connection)
else:
val = self.output_field.get_db_prep_value(val, connection=connection)
if val is None:
# cx_Oracle does not always convert None to the appropriate
# NULL type (like in case expressions using numbers), so we
# use a literal SQL NULL
return 'NULL', []
return '%s', [val]
def resolve_expression(self, query=None, allow_joins=True, reuse=None, summarize=False, for_save=False):
c = super(Value, self).resolve_expression(query, allow_joins, reuse, summarize, for_save)
c.for_save = for_save
return c
def get_group_by_cols(self):
return []
class DurationValue(Value):
def as_sql(self, compiler, connection):
connection.ops.check_expression_support(self)
if (connection.features.has_native_duration_field and
connection.features.driver_supports_timedelta_args):
return super(DurationValue, self).as_sql(compiler, connection)
return connection.ops.date_interval_sql(self.value)
class RawSQL(Expression):
def __init__(self, sql, params, output_field=None):
if output_field is None:
output_field = fields.Field()
self.sql, self.params = sql, params
super(RawSQL, self).__init__(output_field=output_field)
def __repr__(self):
return "{}({}, {})".format(self.__class__.__name__, self.sql, self.params)
def as_sql(self, compiler, connection):
return '(%s)' % self.sql, self.params
def get_group_by_cols(self):
return [self]
class Random(Expression):
def __init__(self):
super(Random, self).__init__(output_field=fields.FloatField())
def __repr__(self):
return "Random()"
def as_sql(self, compiler, connection):
return connection.ops.random_function_sql(), []
class Col(Expression):
def __init__(self, alias, target, output_field=None):
if output_field is None:
output_field = target
super(Col, self).__init__(output_field=output_field)
self.alias, self.target = alias, target
def __repr__(self):
return "{}({}, {})".format(
self.__class__.__name__, self.alias, self.target)
def as_sql(self, compiler, connection):
qn = compiler.quote_name_unless_alias
return "%s.%s" % (qn(self.alias), qn(self.target.column)), []
def relabeled_clone(self, relabels):
return self.__class__(relabels.get(self.alias, self.alias), self.target, self.output_field)
def get_group_by_cols(self):
return [self]
def get_db_converters(self, connection):
if self.target == self.output_field:
return self.output_field.get_db_converters(connection)
return (self.output_field.get_db_converters(connection) +
self.target.get_db_converters(connection))
class Ref(Expression):
"""
Reference to column alias of the query. For example, Ref('sum_cost') in
qs.annotate(sum_cost=Sum('cost')) query.
"""
def __init__(self, refs, source):
super(Ref, self).__init__()
self.refs, self.source = refs, source
def __repr__(self):
return "{}({}, {})".format(self.__class__.__name__, self.refs, self.source)
def get_source_expressions(self):
return [self.source]
def set_source_expressions(self, exprs):
self.source, = exprs
def resolve_expression(self, query=None, allow_joins=True, reuse=None, summarize=False, for_save=False):
# The sub-expression `source` has already been resolved, as this is
# just a reference to the name of `source`.
return self
def relabeled_clone(self, relabels):
return self
def as_sql(self, compiler, connection):
return "%s" % connection.ops.quote_name(self.refs), []
def get_group_by_cols(self):
return [self]
class ExpressionWrapper(Expression):
"""
An expression that can wrap another expression so that it can provide
extra context to the inner expression, such as the output_field.
"""
def __init__(self, expression, output_field):
super(ExpressionWrapper, self).__init__(output_field=output_field)
self.expression = expression
def set_source_expressions(self, exprs):
self.expression = exprs[0]
def get_source_expressions(self):
return [self.expression]
def as_sql(self, compiler, connection):
return self.expression.as_sql(compiler, connection)
def __repr__(self):
return "{}({})".format(self.__class__.__name__, self.expression)
class When(Expression):
template = 'WHEN %(condition)s THEN %(result)s'
def __init__(self, condition=None, then=None, **lookups):
if lookups and condition is None:
condition, lookups = Q(**lookups), None
if condition is None or not isinstance(condition, Q) or lookups:
raise TypeError("__init__() takes either a Q object or lookups as keyword arguments")
super(When, self).__init__(output_field=None)
self.condition = condition
self.result = self._parse_expressions(then)[0]
def __str__(self):
return "WHEN %r THEN %r" % (self.condition, self.result)
def __repr__(self):
return "<%s: %s>" % (self.__class__.__name__, self)
def get_source_expressions(self):
return [self.condition, self.result]
def set_source_expressions(self, exprs):
self.condition, self.result = exprs
def get_source_fields(self):
# We're only interested in the fields of the result expressions.
return [self.result._output_field_or_none]
def resolve_expression(self, query=None, allow_joins=True, reuse=None, summarize=False, for_save=False):
c = self.copy()
c.is_summary = summarize
c.condition = c.condition.resolve_expression(query, allow_joins, reuse, summarize, False)
c.result = c.result.resolve_expression(query, allow_joins, reuse, summarize, for_save)
return c
def as_sql(self, compiler, connection, template=None):
connection.ops.check_expression_support(self)
template_params = {}
sql_params = []
condition_sql, condition_params = compiler.compile(self.condition)
template_params['condition'] = condition_sql
sql_params.extend(condition_params)
result_sql, result_params = compiler.compile(self.result)
template_params['result'] = result_sql
sql_params.extend(result_params)
template = template or self.template
return template % template_params, sql_params
def get_group_by_cols(self):
# This is not a complete expression and cannot be used in GROUP BY.
cols = []
for source in self.get_source_expressions():
cols.extend(source.get_group_by_cols())
return cols
class Case(Expression):
"""
An SQL searched CASE expression:
CASE
WHEN n > 0
THEN 'positive'
WHEN n < 0
THEN 'negative'
ELSE 'zero'
END
"""
template = 'CASE %(cases)s ELSE %(default)s END'
case_joiner = ' '
def __init__(self, *cases, **extra):
if not all(isinstance(case, When) for case in cases):
raise TypeError("Positional arguments must all be When objects.")
default = extra.pop('default', None)
output_field = extra.pop('output_field', None)
super(Case, self).__init__(output_field)
self.cases = list(cases)
self.default = self._parse_expressions(default)[0]
def __str__(self):
return "CASE %s, ELSE %r" % (', '.join(str(c) for c in self.cases), self.default)
def __repr__(self):
return "<%s: %s>" % (self.__class__.__name__, self)
def get_source_expressions(self):
return self.cases + [self.default]
def set_source_expressions(self, exprs):
self.cases = exprs[:-1]
self.default = exprs[-1]
def resolve_expression(self, query=None, allow_joins=True, reuse=None, summarize=False, for_save=False):
c = self.copy()
c.is_summary = summarize
for pos, case in enumerate(c.cases):
c.cases[pos] = case.resolve_expression(query, allow_joins, reuse, summarize, for_save)
c.default = c.default.resolve_expression(query, allow_joins, reuse, summarize, for_save)
return c
def copy(self):
c = super(Case, self).copy()
c.cases = c.cases[:]
return c
def as_sql(self, compiler, connection, template=None, extra=None):
connection.ops.check_expression_support(self)
if not self.cases:
return compiler.compile(self.default)
template_params = dict(extra) if extra else {}
case_parts = []
sql_params = []
for case in self.cases:
case_sql, case_params = compiler.compile(case)
case_parts.append(case_sql)
sql_params.extend(case_params)
template_params['cases'] = self.case_joiner.join(case_parts)
default_sql, default_params = compiler.compile(self.default)
template_params['default'] = default_sql
sql_params.extend(default_params)
template = template or self.template
sql = template % template_params
if self._output_field_or_none is not None:
sql = connection.ops.unification_cast_sql(self.output_field) % sql
return sql, sql_params
class Date(Expression):
"""
Add a date selection column.
"""
def __init__(self, lookup, lookup_type):
super(Date, self).__init__(output_field=fields.DateField())
self.lookup = lookup
self.col = None
self.lookup_type = lookup_type
def __repr__(self):
return "{}({}, {})".format(self.__class__.__name__, self.lookup, self.lookup_type)
def get_source_expressions(self):
return [self.col]
def set_source_expressions(self, exprs):
self.col, = exprs
def resolve_expression(self, query=None, allow_joins=True, reuse=None, summarize=False, for_save=False):
copy = self.copy()
copy.col = query.resolve_ref(self.lookup, allow_joins, reuse, summarize)
field = copy.col.output_field
assert isinstance(field, fields.DateField), "%r isn't a DateField." % field.name
if settings.USE_TZ:
assert not isinstance(field, fields.DateTimeField), (
"%r is a DateTimeField, not a DateField." % field.name
)
return copy
def as_sql(self, compiler, connection):
sql, params = self.col.as_sql(compiler, connection)
assert not(params)
return connection.ops.date_trunc_sql(self.lookup_type, sql), []
def copy(self):
copy = super(Date, self).copy()
copy.lookup = self.lookup
copy.lookup_type = self.lookup_type
return copy
def convert_value(self, value, expression, connection, context):
if isinstance(value, datetime.datetime):
value = value.date()
return value
class DateTime(Expression):
"""
Add a datetime selection column.
"""
def __init__(self, lookup, lookup_type, tzinfo):
super(DateTime, self).__init__(output_field=fields.DateTimeField())
self.lookup = lookup
self.col = None
self.lookup_type = lookup_type
if tzinfo is None:
self.tzname = None
else:
self.tzname = timezone._get_timezone_name(tzinfo)
self.tzinfo = tzinfo
def __repr__(self):
return "{}({}, {}, {})".format(
self.__class__.__name__, self.lookup, self.lookup_type, self.tzinfo)
def get_source_expressions(self):
return [self.col]
def set_source_expressions(self, exprs):
self.col, = exprs
def resolve_expression(self, query=None, allow_joins=True, reuse=None, summarize=False, for_save=False):
copy = self.copy()
copy.col = query.resolve_ref(self.lookup, allow_joins, reuse, summarize)
field = copy.col.output_field
assert isinstance(field, fields.DateTimeField), (
"%r isn't a DateTimeField." % field.name
)
return copy
def as_sql(self, compiler, connection):
sql, params = self.col.as_sql(compiler, connection)
assert not(params)
return connection.ops.datetime_trunc_sql(self.lookup_type, sql, self.tzname)
def copy(self):
copy = super(DateTime, self).copy()
copy.lookup = self.lookup
copy.lookup_type = self.lookup_type
copy.tzname = self.tzname
return copy
def convert_value(self, value, expression, connection, context):
if settings.USE_TZ:
if value is None:
raise ValueError(
"Database returned an invalid value in QuerySet.datetimes(). "
"Are time zone definitions for your database and pytz installed?"
)
value = value.replace(tzinfo=None)
value = timezone.make_aware(value, self.tzinfo)
return value
class OrderBy(BaseExpression):
template = '%(expression)s %(ordering)s'
def __init__(self, expression, descending=False):
self.descending = descending
if not hasattr(expression, 'resolve_expression'):
raise ValueError('expression must be an expression type')
self.expression = expression
def __repr__(self):
return "{}({}, descending={})".format(
self.__class__.__name__, self.expression, self.descending)
def set_source_expressions(self, exprs):
self.expression = exprs[0]
def get_source_expressions(self):
return [self.expression]
def as_sql(self, compiler, connection):
connection.ops.check_expression_support(self)
expression_sql, params = compiler.compile(self.expression)
placeholders = {'expression': expression_sql}
placeholders['ordering'] = 'DESC' if self.descending else 'ASC'
return (self.template % placeholders).rstrip(), params
def get_group_by_cols(self):
cols = []
for source in self.get_source_expressions():
cols.extend(source.get_group_by_cols())
return cols
def reverse_ordering(self):
self.descending = not self.descending
return self
def asc(self):
self.descending = False
def desc(self):
self.descending = True