# Django 2.2.9.dev20191202104323 文档

# django.db.models.functions.datetime 源代码

    from datetime import datetime

    from django.conf import settings
    from django.db.models.expressions import Func
    from django.db.models.fields import (
        DateField, DateTimeField, DurationField, Field, IntegerField, TimeField,
    )
    from django.db.models.lookups import (
        Transform, YearExact, YearGt, YearGte, YearLt, YearLte,
    )
    from django.utils import timezone

    class TimezoneMixin:
        tzinfo = None

        def get_tzname(self):
            # Timezone conversions must happen to the input datetime *before*
            # applying a function. 2015-12-31 23:00:00 -02:00 is stored in the
            # database as 2016-01-01 01:00:00 +00:00. Any results should be
            # based on the input datetime not the stored datetime.
            tzname = None
            if settings.USE_TZ:
                if self.tzinfo is None:
                    tzname = timezone.get_current_timezone_name()
                else:
                    tzname = timezone._get_timezone_name(self.tzinfo)
            return tzname

    class Extract(TimezoneMixin, Transform):
        lookup_name = None
        output_field = IntegerField()

        def __init__(self, expression, lookup_name=None, tzinfo=None, **extra):
            if self.lookup_name is None:
                self.lookup_name = lookup_name
            if self.lookup_name is None:
                raise ValueError('lookup_name must be provided')
            self.tzinfo = tzinfo
            super().__init__(expression, **extra)

        def as_sql(self, compiler, connection):
            sql, params = compiler.compile(self.lhs)
            lhs_output_field = self.lhs.output_field
            if isinstance(lhs_output_field, DateTimeField):
                tzname = self.get_tzname()
                sql = connection.ops.datetime_extract_sql(self.lookup_name, sql, tzname)
            elif isinstance(lhs_output_field, DateField):
                sql = connection.ops.date_extract_sql(self.lookup_name, sql)
            elif isinstance(lhs_output_field, TimeField):
                sql = connection.ops.time_extract_sql(self.lookup_name, sql)
            elif isinstance(lhs_output_field, DurationField):
                if not connection.features.has_native_duration_field:
                    raise ValueError('Extract requires native DurationField database support.')
                sql = connection.ops.time_extract_sql(self.lookup_name, sql)
            else:
                # resolve_expression has already validated the output_field so this
                # assert should never be hit.
                assert False, "Tried to Extract from an invalid type."
            return sql, params

        def resolve_expression(self, query=None, allow_joins=True, reuse=None, summarize=False, for_save=False):
            copy = super().resolve_expression(query, allow_joins, reuse, summarize, for_save)
            field = copy.lhs.output_field
            if not isinstance(field, (DateField, DateTimeField, TimeField, DurationField)):
                raise ValueError(
                    'Extract input expression must be DateField, DateTimeField, '
                    'TimeField, or DurationField.'
                )
            # Passing dates to functions expecting datetimes is most likely a mistake.
            if type(field) == DateField and copy.lookup_name in ('hour', 'minute', 'second'):
                raise ValueError(
                    "Cannot extract time component '%s' from DateField '%s'. " % (copy.lookup_name, field.name)
                )
            return copy

    class ExtractYear(Extract):
        lookup_name = 'year'

    class ExtractIsoYear(Extract):
        """Return the ISO-8601 week-numbering year."""
        lookup_name = 'iso_year'

    class ExtractMonth(Extract):
        lookup_name = 'month'

    class ExtractDay(Extract):
        lookup_name = 'day'

    class ExtractWeek(Extract):
        """
        Return 1-52 or 53, based on ISO-8601, i.e., Monday is the first of the
        week.
        """
        lookup_name = 'week'

    class ExtractWeekDay(Extract):
        """
        Return Sunday=1 through Saturday=7.

        To replicate this in Python: (mydatetime.isoweekday() % 7) + 1
        """
        lookup_name = 'week_day'

    class ExtractQuarter(Extract):
        lookup_name = 'quarter'

    class ExtractHour(Extract):
        lookup_name = 'hour'

    class ExtractMinute(Extract):
        lookup_name = 'minute'

    class ExtractSecond(Extract):
        lookup_name = 'second'

    DateField.register_lookup(ExtractYear)
    DateField.register_lookup(ExtractMonth)
    DateField.register_lookup(ExtractDay)
    DateField.register_lookup(ExtractWeekDay)
    DateField.register_lookup(ExtractWeek)
    DateField.register_lookup(ExtractIsoYear)
    DateField.register_lookup(ExtractQuarter)

    TimeField.register_lookup(ExtractHour)
    TimeField.register_lookup(ExtractMinute)
    TimeField.register_lookup(ExtractSecond)

    DateTimeField.register_lookup(ExtractHour)
    DateTimeField.register_lookup(ExtractMinute)
    DateTimeField.register_lookup(ExtractSecond)

    ExtractYear.register_lookup(YearExact)
    ExtractYear.register_lookup(YearGt)
    ExtractYear.register_lookup(YearGte)
    ExtractYear.register_lookup(YearLt)
    ExtractYear.register_lookup(YearLte)

    ExtractIsoYear.register_lookup(YearExact)
    ExtractIsoYear.register_lookup(YearGt)
    ExtractIsoYear.register_lookup(YearGte)
    ExtractIsoYear.register_lookup(YearLt)
    ExtractIsoYear.register_lookup(YearLte)

    class Now(Func):
        template = 'CURRENT_TIMESTAMP'
        output_field = DateTimeField()

        def as_postgresql(self, compiler, connection, **extra_context):
            # PostgreSQL's CURRENT_TIMESTAMP means "the time at the start of the
            # transaction". Use STATEMENT_TIMESTAMP to be cross-compatible with
            # other databases.
            return self.as_sql(compiler, connection, template='STATEMENT_TIMESTAMP()', **extra_context)

    class TruncBase(TimezoneMixin, Transform):
        kind = None
        tzinfo = None

        def __init__(self, expression, output_field=None, tzinfo=None, **extra):
            self.tzinfo = tzinfo
            super().__init__(expression, output_field=output_field, **extra)

        def as_sql(self, compiler, connection):
            inner_sql, inner_params = compiler.compile(self.lhs)
            if isinstance(self.output_field, DateTimeField):
                tzname = self.get_tzname()
                sql = connection.ops.datetime_trunc_sql(self.kind, inner_sql, tzname)
            elif isinstance(self.output_field, DateField):
                sql = connection.ops.date_trunc_sql(self.kind, inner_sql)
            elif isinstance(self.output_field, TimeField):
                sql = connection.ops.time_trunc_sql(self.kind, inner_sql)
            else:
                raise ValueError('Trunc only valid on DateField, TimeField, or DateTimeField.')
            return sql, inner_params

        def resolve_expression(self, query=None, allow_joins=True, reuse=None, summarize=False, for_save=False):
            copy = super().resolve_expression(query, allow_joins, reuse, summarize, for_save)
            field = copy.lhs.output_field
            # DateTimeField is a subclass of DateField so this works for both.
            assert isinstance(field, (DateField, TimeField)), (
                "%r isn't a DateField, TimeField, or DateTimeField." % field.name
            )
            # If self.output_field was None, then accessing the field will trigger
            # the resolver to assign it to self.lhs.output_field.
            if not isinstance(copy.output_field, (DateField, DateTimeField, TimeField)):
                raise ValueError('output_field must be either DateField, TimeField, or DateTimeField')
            # Passing dates or times to functions expecting datetimes is most
            # likely a mistake.
            class_output_field = self.__class__.output_field if isinstance(self.__class__.output_field, Field) else None
            output_field = class_output_field or copy.output_field
            has_explicit_output_field = class_output_field or field.__class__ is not copy.output_field.__class__
            if type(field) == DateField and (
                    isinstance(output_field, DateTimeField) or copy.kind in ('hour', 'minute', 'second', 'time')):
                raise ValueError("Cannot truncate DateField '%s' to %s. " % (
                    field.name, output_field.__class__.__name__ if has_explicit_output_field else 'DateTimeField'
                ))
            elif isinstance(field, TimeField) and (
                    isinstance(output_field, DateTimeField) or
                    copy.kind in ('year', 'quarter', 'month', 'week', 'day', 'date')):
                raise ValueError("Cannot truncate TimeField '%s' to %s. " % (
                    field.name, output_field.__class__.__name__ if has_explicit_output_field else 'DateTimeField'
                ))
            return copy

        def convert_value(self, value, expression, connection):
            if isinstance(self.output_field, DateTimeField):
                if not settings.USE_TZ:
                    pass
                elif value is not None:
                    value = value.replace(tzinfo=None)
                    value = timezone.make_aware(value, self.tzinfo)
                elif not connection.features.has_zoneinfo_database:
                    raise ValueError(
                        'Database returned an invalid datetime value. Are time '
                        'zone definitions for your database installed?'
                    )
            elif isinstance(value, datetime):
                if value is None:
                    pass
                elif isinstance(self.output_field, DateField):
                    value = value.date()
                elif isinstance(self.output_field, TimeField):
                    value = value.time()
            return value

    class Trunc(TruncBase):

        def __init__(self, expression, kind, output_field=None, tzinfo=None, **extra):
            self.kind = kind
            super().__init__(expression, output_field=output_field, tzinfo=tzinfo, **extra)

    class TruncYear(TruncBase):
        kind = 'year'

    class TruncQuarter(TruncBase):
        kind = 'quarter'

    class TruncMonth(TruncBase):
        kind = 'month'

    class TruncWeek(TruncBase):
        """Truncate to midnight on the Monday of the week."""
        kind = 'week'

    class TruncDay(TruncBase):
        kind = 'day'

    class TruncDate(TruncBase):
        kind = 'date'
        lookup_name = 'date'
        output_field = DateField()

        def as_sql(self, compiler, connection):
            # Cast to date rather than truncate to date.
            lhs, lhs_params = compiler.compile(self.lhs)
            tzname = timezone.get_current_timezone_name() if settings.USE_TZ else None
            sql = connection.ops.datetime_cast_date_sql(lhs, tzname)
            return sql, lhs_params

    class TruncTime(TruncBase):
        kind = 'time'
        lookup_name = 'time'
        output_field = TimeField()

        def as_sql(self, compiler, connection):
            # Cast to time rather than truncate to time.
            lhs, lhs_params = compiler.compile(self.lhs)
            tzname = timezone.get_current_timezone_name() if settings.USE_TZ else None
            sql = connection.ops.datetime_cast_time_sql(lhs, tzname)
            return sql, lhs_params

    class TruncHour(TruncBase):
        kind = 'hour'

    class TruncMinute(TruncBase):
        kind = 'minute'

    class TruncSecond(TruncBase):
        kind = 'second'

    DateTimeField.register_lookup(TruncDate)
    DateTimeField.register_lookup(TruncTime)