django.db.models.expressions.BaseExpression

class documentation

class BaseExpression:

Known subclasses: django.db.models.expressions.Expression, django.db.models.expressions.Subquery, django.db.models.sql.query.Query

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Base class for all query expressions.

Static Method	`_convert_value_noop`	Undocumented
Method	`__getstate__`	Undocumented
Method	`__init__`	Undocumented
Method	`_parse_expressions`	Undocumented
Method	`_resolve_output_field`	Attempt to infer the output type of the expression. If the output fields of all source fields match then, simply infer the same type here. This isn't always correct, but it makes sense most of the time.
Method	`as_sql`	Responsible for returning a (sql, [params]) tuple to be included in the current query.
Method	`asc`	Undocumented
Method	`copy`	Undocumented
Method	`desc`	Undocumented
Method	`flatten`	Recursively yield this expression and all subexpressions, in depth-first order.
Method	`get_db_converters`	Undocumented
Method	`get_group_by_cols`	Undocumented
Method	`get_lookup`	Undocumented
Method	`get_source_expressions`	Undocumented
Method	`get_source_fields`	Return the underlying field types used by this aggregate.
Method	`get_transform`	Undocumented
Method	`relabeled_clone`	Undocumented
Method	`resolve_expression`	Provide the chance to do any preprocessing or validation before being added to the query.
Method	`reverse_ordering`	Undocumented
Method	`select_format`	Custom format for select clauses. For example, EXISTS expressions need to be wrapped in CASE WHEN on Oracle.
Method	`set_source_expressions`	Undocumented
Class Variable	`_output_field_resolved_to_none`	Undocumented
Class Variable	`filterable`	Undocumented
Class Variable	`is_summary`	Undocumented
Class Variable	`window_compatible`	Undocumented
Property	`_output_field_or_none`	Return the output field of this expression, or None if _resolve_output_field() didn't return an output type.
Property	`conditional`	Undocumented
Property	`contains_aggregate`	Undocumented
Property	`contains_column_references`	Undocumented
Property	`contains_over_clause`	Undocumented
Property	`convert_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.
Property	`field`	Undocumented
Property	`output_field`	Return the output type of this expressions.

@staticmethod
def _convert_value_noop(value, expression, connection):

Undocumented

def __getstate__(self):

Undocumented

def __init__(self, output_field=None):

overridden in django.db.models.expressions.Case, django.db.models.expressions.RawSQL, django.db.models.expressions.When, django.db.models.expressions.Window, django.contrib.postgres.fields.ranges.RangeBoundary, django.db.models.expressions.Col, django.db.models.expressions.CombinedExpression, django.db.models.expressions.ExpressionWrapper, django.db.models.expressions.Func, django.db.models.expressions.OrderBy, django.db.models.expressions.Ref, django.db.models.expressions.Subquery, django.db.models.expressions.Value, django.db.models.expressions.WindowFrame, django.db.models.lookups.Lookup, django.db.models.sql.query.Query

Undocumented

def _parse_expressions(self, *expressions):

Undocumented

def _resolve_output_field(self):

overridden in django.db.models.expressions.Window, django.db.models.functions.Round, django.db.models.expressions.CombinedExpression, django.db.models.expressions.Subquery, django.db.models.expressions.Value, django.db.models.functions.window.LagLeadFunction, django.db.models.functions.window.NthValue

Attempt to infer the output type of the expression. If the output fields of all source fields match then, 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's output field resolves to None, exclude it from this check. If all sources are None, then an error is raised higher up the stack in the output_field property.

def as_sql(self, compiler, connection):

overridden in django.db.models.expressions.Case, django.db.models.expressions.RawSQL, django.db.models.expressions.When, django.db.models.expressions.Window, django.contrib.postgres.fields.ranges.RangeBoundary, django.db.models.expressions.Col, django.db.models.expressions.CombinedExpression, django.db.models.expressions.ExpressionWrapper, django.db.models.expressions.Func, django.db.models.expressions.OrderBy, django.db.models.expressions.Ref, django.db.models.expressions.Star, django.db.models.expressions.Subquery, django.db.models.expressions.Value, django.db.models.expressions.WindowFrame, django.db.models.fields.json.ContainedBy, django.db.models.fields.json.DataContains, django.db.models.fields.json.HasKeyLookup, django.db.models.lookups.BuiltinLookup, django.db.models.lookups.YearLookup, django.db.models.sql.query.Query

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 asc(self, **kwargs):

overridden in django.db.models.expressions.OrderBy

Undocumented

def copy(self):

overridden in django.db.models.expressions.Case, django.db.models.expressions.Func, django.db.models.expressions.Subquery

Undocumented

def desc(self, **kwargs):

overridden in django.db.models.expressions.OrderBy

Undocumented

def flatten(self):

Recursively yield this expression and all subexpressions, in depth-first order.

def get_db_converters(self, connection):

overridden in django.db.models.expressions.Col

Undocumented

def get_group_by_cols(self, alias=None):

Undocumented

def get_lookup(self, lookup):

Undocumented

def get_source_expressions(self):

overridden in django.db.models.expressions.Case, django.db.models.expressions.When, django.db.models.expressions.Window, django.db.models.expressions.CombinedExpression, django.db.models.expressions.ExpressionWrapper, django.db.models.expressions.Func, django.db.models.expressions.OrderBy, django.db.models.expressions.Ref, django.db.models.expressions.Subquery, django.db.models.expressions.WindowFrame, django.db.models.lookups.Lookup

Undocumented

def get_source_fields(self):

overridden in django.db.models.expressions.When, django.db.models.aggregates.Aggregate

Return the underlying field types used by this aggregate.

def get_transform(self, name):

Undocumented

def relabeled_clone(self, change_map):

overridden in django.db.models.expressions.Col, django.db.models.expressions.Ref, django.db.models.sql.query.Query

Undocumented

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.

def reverse_ordering(self):

overridden in django.db.models.expressions.OrderBy

Undocumented

def select_format(self, compiler, sql, params):

overridden in django.db.models.expressions.Exists, django.db.models.lookups.Lookup

Custom format for select clauses. For example, EXISTS expressions need to be wrapped in CASE WHEN on Oracle.

def set_source_expressions(self, exprs):

Undocumented

_output_field_resolved_to_none: bool =

Undocumented

filterable: bool =

overridden in django.db.models.expressions.Window

Undocumented

is_summary: bool =

Undocumented

window_compatible: bool =

overridden in django.db.models.aggregates.Aggregate, django.db.models.functions.window.CumeDist, django.db.models.functions.window.DenseRank, django.db.models.functions.window.FirstValue, django.db.models.functions.window.LagLeadFunction, django.db.models.functions.window.LastValue, django.db.models.functions.window.NthValue, django.db.models.functions.window.Ntile, django.db.models.functions.window.PercentRank, django.db.models.functions.window.Rank, django.db.models.functions.window.RowNumber

Undocumented

@cached_property
_output_field_or_none =

Return the output field of this expression, or None if _resolve_output_field() didn't return an output type.

@property
conditional =

overridden in django.db.models.expressions.When, django.db.models.expressions.OrderBy

Undocumented

@cached_property
contains_aggregate =

overridden in django.db.models.expressions.Window, django.db.models.aggregates.Aggregate, django.db.models.expressions.Subquery

Undocumented

@cached_property
contains_column_references =

overridden in django.db.models.expressions.Col

Undocumented

@cached_property
contains_over_clause =

overridden in django.db.models.expressions.Window

Undocumented

@cached_property
convert_value =

overridden in django.db.models.functions.datetime.TruncBase

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.

@property
field =

Undocumented

@cached_property
output_field =

overridden in django.db.models.functions.Extract, django.db.models.functions.JSONObject, django.db.models.functions.Left, django.db.models.functions.Length, django.db.models.functions.LPad, django.db.models.functions.Now, django.db.models.functions.Ord, django.db.models.functions.Repeat, django.db.models.functions.StrIndex, django.db.models.functions.Substr, django.db.models.functions.TruncDate, django.db.models.functions.TruncTime, django.contrib.postgres.fields.ranges.IsEmpty, django.contrib.postgres.fields.ranges.LowerInclusive, django.contrib.postgres.fields.ranges.LowerInfinite, django.contrib.postgres.fields.ranges.RangeEndsWith, django.contrib.postgres.fields.ranges.RangeStartsWith, django.contrib.postgres.fields.ranges.UpperInclusive, django.contrib.postgres.fields.ranges.UpperInfinite, django.db.models.aggregates.Count, django.db.models.expressions.Exists, django.db.models.expressions.TemporalSubtraction, django.db.models.functions.window.CumeDist, django.db.models.functions.window.DenseRank, django.db.models.functions.window.Ntile, django.db.models.functions.window.PercentRank, django.db.models.functions.window.Rank, django.db.models.functions.window.RowNumber, django.db.models.lookups.Lookup, django.db.models.sql.query.Query

Return the output type of this expressions.