class TruncHour

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().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.

Return: (sql, params)
  Where `sql` is a string containing ordered sql parameters to be
  replaced with the elements of the list `params`.

    def as_sql(self, compiler, connection):
        sql, params = compiler.compile(self.lhs)
        tzname = None
        if isinstance(self.lhs.output_field, DateTimeField):
            tzname = self.get_tzname()
        elif self.tzinfo is not None:
            raise ValueError("tzinfo can only be used with DateTimeField.")
        if isinstance(self.output_field, DateTimeField):
            sql, params = connection.ops.datetime_trunc_sql(
                self.kind, sql, tuple(params), tzname
            )
        elif isinstance(self.output_field, DateField):
            sql, params = connection.ops.date_trunc_sql(
                self.kind, sql, tuple(params), tzname
            )
        elif isinstance(self.output_field, TimeField):
            sql, params = connection.ops.time_trunc_sql(
                self.kind, sql, tuple(params), tzname
            )
        else:
            raise ValueError(
                "Trunc only valid on DateField, TimeField, or DateTimeField."
            )
        return sql, params

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().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.

Return: (sql, params)
  Where `sql` is a string containing ordered sql parameters to be
  replaced with the elements of the list `params`.

    def as_sql(
        self,
        compiler,
        connection,
        function=None,
        template=None,
        arg_joiner=None,
        **extra_context,
    ):
        connection.ops.check_expression_support(self)
        sql_parts = []
        params = []
        for arg in self.source_expressions:
            try:
                arg_sql, arg_params = compiler.compile(arg)
            except EmptyResultSet:
                empty_result_set_value = getattr(
                    arg, "empty_result_set_value", NotImplemented
                )
                if empty_result_set_value is NotImplemented:
                    raise
                arg_sql, arg_params = compiler.compile(Value(empty_result_set_value))
            except FullResultSet:
                arg_sql, arg_params = compiler.compile(Value(True))
            sql_parts.append(arg_sql)
            params.extend(arg_params)
        data = {**self.extra, **extra_context}
        # Use the first supplied value in this order: the parameter to this
        # method, a value supplied in __init__()'s **extra (the value in
        # `data`), or the value defined on the class.
        if function is not None:
            data["function"] = function
        else:
            data.setdefault("function", self.function)
        template = template or data.get("template", self.template)
        arg_joiner = arg_joiner or data.get("arg_joiner", self.arg_joiner)
        data["expressions"] = data["field"] = arg_joiner.join(sql_parts)
        return template % data, params

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().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.

Return: (sql, params)
  Where `sql` is a string containing ordered sql parameters to be
  replaced with the elements of the list `params`.

    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().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.

        Return: (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()")

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.

    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

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.

    def copy(self):
        copy = super().copy()
        copy.source_expressions = self.source_expressions[:]
        copy.extra = self.extra.copy()
        return copy

    def copy(self):
        return copy.copy(self)

Return a 3-tuple of class import path, positional arguments,
and keyword arguments.

        def deconstruct(obj):
            """
            Return a 3-tuple of class import path, positional arguments,
            and keyword arguments.
            """
            # Fallback version
            if path and type(obj) is klass:
                module_name, _, name = path.rpartition(".")
            else:
                module_name = obj.__module__
                name = obj.__class__.__name__
            # Make sure it's actually there and not an inner class
            module = import_module(module_name)
            if not hasattr(module, name):
                raise ValueError(
                    "Could not find object %s in %s.\n"
                    "Please note that you cannot serialize things like inner "
                    "classes. Please move the object into the main module "
                    "body to use migrations.\n"
                    "For more information, see "
                    "https://docs.djangoproject.com/en/%s/topics/migrations/"
                    "#serializing-values" % (name, module_name, get_docs_version())
                )
            return (
                (
                    path
                    if path and type(obj) is klass
                    else f"{obj.__class__.__module__}.{name}"
                ),
                obj._constructor_args[0],
                obj._constructor_args[1],
            )

Return a 3-tuple of class import path, positional arguments,
and keyword arguments.

        def deconstruct(obj):
            """
            Return a 3-tuple of class import path, positional arguments,
            and keyword arguments.
            """
            # Fallback version
            if path and type(obj) is klass:
                module_name, _, name = path.rpartition(".")
            else:
                module_name = obj.__module__
                name = obj.__class__.__name__
            # Make sure it's actually there and not an inner class
            module = import_module(module_name)
            if not hasattr(module, name):
                raise ValueError(
                    "Could not find object %s in %s.\n"
                    "Please note that you cannot serialize things like inner "
                    "classes. Please move the object into the main module "
                    "body to use migrations.\n"
                    "For more information, see "
                    "https://docs.djangoproject.com/en/%s/topics/migrations/"
                    "#serializing-values" % (name, module_name, get_docs_version())
                )
            return (
                (
                    path
                    if path and type(obj) is klass
                    else f"{obj.__class__.__module__}.{name}"
                ),
                obj._constructor_args[0],
                obj._constructor_args[1],
            )

    def get_lookup(self, lookup_name):
        from django.db.models.lookups import Lookup

        found = self._get_lookup(lookup_name)
        if found is None and hasattr(self, "output_field"):
            return self.output_field.get_lookup(lookup_name)
        if found is not None and not issubclass(found, Lookup):
            return None
        return found

    def get_lookup(self, lookup):
        return self.output_field.get_lookup(lookup)

    def get_source_expressions(self):
        return self.source_expressions

    def get_source_expressions(self):
        return []

    def get_transform(self, lookup_name):
        from django.db.models.lookups import Transform

        found = self._get_lookup(lookup_name)
        if found is None and hasattr(self, "output_field"):
            return self.output_field.get_transform(lookup_name)
        if found is not None and not issubclass(found, Transform):
            return None
        return found

    def get_transform(self, name):
        return self.output_field.get_transform(name)

Provide 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

Return: an Expression to be added to the query.

    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.
        if not isinstance(field, (DateField, TimeField)):
            raise TypeError(
                "%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) is 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

Provide 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

Return: an Expression to be added to the query.

    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

Provide 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

Return: an Expression to be added to the query.

    def resolve_expression(
        self, query=None, allow_joins=True, reuse=None, summarize=False, for_save=False
    ):
        """
        Provide 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

        Return: 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)
                    if expr
                    else None
                )
                for expr in c.get_source_expressions()
            ]
        )
        return c

    def set_source_expressions(self, exprs):
        self.source_expressions = exprs

    def set_source_expressions(self, exprs):
        assert not exprs