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# sql/functions.py
# Copyright (C) 2005-2016 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
"""SQL function API, factories, and built-in functions.
"""
from . import sqltypes, schema
from .base import Executable, ColumnCollection
from .elements import ClauseList, Cast, Extract, _literal_as_binds, \
literal_column, _type_from_args, ColumnElement, _clone,\
Over, BindParameter, FunctionFilter
from .selectable import FromClause, Select, Alias
from . import operators
from .visitors import VisitableType
from .. import util
from . import annotation
_registry = util.defaultdict(dict)
def register_function(identifier, fn, package="_default"):
"""Associate a callable with a particular func. name.
This is normally called by _GenericMeta, but is also
available by itself so that a non-Function construct
can be associated with the :data:`.func` accessor (i.e.
CAST, EXTRACT).
"""
reg = _registry[package]
reg[identifier] = fn
class FunctionElement(Executable, ColumnElement, FromClause):
"""Base for SQL function-oriented constructs.
.. seealso::
:class:`.Function` - named SQL function.
:data:`.func` - namespace which produces registered or ad-hoc
:class:`.Function` instances.
:class:`.GenericFunction` - allows creation of registered function
types.
"""
packagenames = ()
def __init__(self, *clauses, **kwargs):
"""Construct a :class:`.FunctionElement`.
"""
args = [_literal_as_binds(c, self.name) for c in clauses]
self.clause_expr = ClauseList(
operator=operators.comma_op,
group_contents=True, *args).\
self_group()
def _execute_on_connection(self, connection, multiparams, params):
return connection._execute_function(self, multiparams, params)
@property
def columns(self):
"""The set of columns exported by this :class:`.FunctionElement`.
Function objects currently have no result column names built in;
this method returns a single-element column collection with
an anonymously named column.
An interim approach to providing named columns for a function
as a FROM clause is to build a :func:`.select` with the
desired columns::
from sqlalchemy.sql import column
stmt = select([column('x'), column('y')]).\
select_from(func.myfunction())
"""
return ColumnCollection(self.label(None))
@util.memoized_property
def clauses(self):
"""Return the underlying :class:`.ClauseList` which contains
the arguments for this :class:`.FunctionElement`.
"""
return self.clause_expr.element
def over(self, partition_by=None, order_by=None):
"""Produce an OVER clause against this function.
Used against aggregate or so-called "window" functions,
for database backends that support window functions.
The expression::
func.row_number().over(order_by='x')
is shorthand for::
from sqlalchemy import over
over(func.row_number(), order_by='x')
See :func:`~.expression.over` for a full description.
.. versionadded:: 0.7
"""
return Over(self, partition_by=partition_by, order_by=order_by)
def filter(self, *criterion):
"""Produce a FILTER clause against this function.
Used against aggregate and window functions,
for database backends that support the "FILTER" clause.
The expression::
func.count(1).filter(True)
is shorthand for::
from sqlalchemy import funcfilter
funcfilter(func.count(1), True)
.. versionadded:: 1.0.0
.. seealso::
:class:`.FunctionFilter`
:func:`.funcfilter`
"""
if not criterion:
return self
return FunctionFilter(self, *criterion)
@property
def _from_objects(self):
return self.clauses._from_objects
def get_children(self, **kwargs):
return self.clause_expr,
def _copy_internals(self, clone=_clone, **kw):
self.clause_expr = clone(self.clause_expr, **kw)
self._reset_exported()
FunctionElement.clauses._reset(self)
def alias(self, name=None, flat=False):
"""Produce a :class:`.Alias` construct against this
:class:`.FunctionElement`.
This construct wraps the function in a named alias which
is suitable for the FROM clause, in the style accepted for example
by Postgresql.
e.g.::
from sqlalchemy.sql import column
stmt = select([column('data_view')]).\\
select_from(SomeTable).\\
select_from(func.unnest(SomeTable.data).alias('data_view')
)
Would produce:
.. sourcecode:: sql
SELECT data_view
FROM sometable, unnest(sometable.data) AS data_view
.. versionadded:: 0.9.8 The :meth:`.FunctionElement.alias` method
is now supported. Previously, this method's behavior was
undefined and did not behave consistently across versions.
"""
return Alias(self, name)
def select(self):
"""Produce a :func:`~.expression.select` construct
against this :class:`.FunctionElement`.
This is shorthand for::
s = select([function_element])
"""
s = Select([self])
if self._execution_options:
s = s.execution_options(**self._execution_options)
return s
def scalar(self):
"""Execute this :class:`.FunctionElement` against an embedded
'bind' and return a scalar value.
This first calls :meth:`~.FunctionElement.select` to
produce a SELECT construct.
Note that :class:`.FunctionElement` can be passed to
the :meth:`.Connectable.scalar` method of :class:`.Connection`
or :class:`.Engine`.
"""
return self.select().execute().scalar()
def execute(self):
"""Execute this :class:`.FunctionElement` against an embedded
'bind'.
This first calls :meth:`~.FunctionElement.select` to
produce a SELECT construct.
Note that :class:`.FunctionElement` can be passed to
the :meth:`.Connectable.execute` method of :class:`.Connection`
or :class:`.Engine`.
"""
return self.select().execute()
def _bind_param(self, operator, obj):
return BindParameter(None, obj, _compared_to_operator=operator,
_compared_to_type=self.type, unique=True)
class _FunctionGenerator(object):
"""Generate :class:`.Function` objects based on getattr calls."""
def __init__(self, **opts):
self.__names = []
self.opts = opts
def __getattr__(self, name):
# passthru __ attributes; fixes pydoc
if name.startswith('__'):
try:
return self.__dict__[name]
except KeyError:
raise AttributeError(name)
elif name.endswith('_'):
name = name[0:-1]
f = _FunctionGenerator(**self.opts)
f.__names = list(self.__names) + [name]
return f
def __call__(self, *c, **kwargs):
o = self.opts.copy()
o.update(kwargs)
tokens = len(self.__names)
if tokens == 2:
package, fname = self.__names
elif tokens == 1:
package, fname = "_default", self.__names[0]
else:
package = None
if package is not None:
func = _registry[package].get(fname)
if func is not None:
return func(*c, **o)
return Function(self.__names[-1],
packagenames=self.__names[0:-1], *c, **o)
func = _FunctionGenerator()
"""Generate SQL function expressions.
:data:`.func` is a special object instance which generates SQL
functions based on name-based attributes, e.g.::
>>> print(func.count(1))
count(:param_1)
The element is a column-oriented SQL element like any other, and is
used in that way::
>>> print(select([func.count(table.c.id)]))
SELECT count(sometable.id) FROM sometable
Any name can be given to :data:`.func`. If the function name is unknown to
SQLAlchemy, it will be rendered exactly as is. For common SQL functions
which SQLAlchemy is aware of, the name may be interpreted as a *generic
function* which will be compiled appropriately to the target database::
>>> print(func.current_timestamp())
CURRENT_TIMESTAMP
To call functions which are present in dot-separated packages,
specify them in the same manner::
>>> print(func.stats.yield_curve(5, 10))
stats.yield_curve(:yield_curve_1, :yield_curve_2)
SQLAlchemy can be made aware of the return type of functions to enable
type-specific lexical and result-based behavior. For example, to ensure
that a string-based function returns a Unicode value and is similarly
treated as a string in expressions, specify
:class:`~sqlalchemy.types.Unicode` as the type:
>>> print(func.my_string(u'hi', type_=Unicode) + ' ' +
... func.my_string(u'there', type_=Unicode))
my_string(:my_string_1) || :my_string_2 || my_string(:my_string_3)
The object returned by a :data:`.func` call is usually an instance of
:class:`.Function`.
This object meets the "column" interface, including comparison and labeling
functions. The object can also be passed the :meth:`~.Connectable.execute`
method of a :class:`.Connection` or :class:`.Engine`, where it will be
wrapped inside of a SELECT statement first::
print(connection.execute(func.current_timestamp()).scalar())
In a few exception cases, the :data:`.func` accessor
will redirect a name to a built-in expression such as :func:`.cast`
or :func:`.extract`, as these names have well-known meaning
but are not exactly the same as "functions" from a SQLAlchemy
perspective.
.. versionadded:: 0.8 :data:`.func` can return non-function expression
constructs for common quasi-functional names like :func:`.cast`
and :func:`.extract`.
Functions which are interpreted as "generic" functions know how to
calculate their return type automatically. For a listing of known generic
functions, see :ref:`generic_functions`.
.. note::
The :data:`.func` construct has only limited support for calling
standalone "stored procedures", especially those with special
parameterization concerns.
See the section :ref:`stored_procedures` for details on how to use
the DBAPI-level ``callproc()`` method for fully traditional stored
procedures.
"""
modifier = _FunctionGenerator(group=False)
class Function(FunctionElement):
"""Describe a named SQL function.
See the superclass :class:`.FunctionElement` for a description
of public methods.
.. seealso::
:data:`.func` - namespace which produces registered or ad-hoc
:class:`.Function` instances.
:class:`.GenericFunction` - allows creation of registered function
types.
"""
__visit_name__ = 'function'
def __init__(self, name, *clauses, **kw):
"""Construct a :class:`.Function`.
The :data:`.func` construct is normally used to construct
new :class:`.Function` instances.
"""
self.packagenames = kw.pop('packagenames', None) or []
self.name = name
self._bind = kw.get('bind', None)
self.type = sqltypes.to_instance(kw.get('type_', None))
FunctionElement.__init__(self, *clauses, **kw)
def _bind_param(self, operator, obj):
return BindParameter(self.name, obj,
_compared_to_operator=operator,
_compared_to_type=self.type,
unique=True)
class _GenericMeta(VisitableType):
def __init__(cls, clsname, bases, clsdict):
if annotation.Annotated not in cls.__mro__:
cls.name = name = clsdict.get('name', clsname)
cls.identifier = identifier = clsdict.get('identifier', name)
package = clsdict.pop('package', '_default')
# legacy
if '__return_type__' in clsdict:
cls.type = clsdict['__return_type__']
register_function(identifier, cls, package)
super(_GenericMeta, cls).__init__(clsname, bases, clsdict)
class GenericFunction(util.with_metaclass(_GenericMeta, Function)):
"""Define a 'generic' function.
A generic function is a pre-established :class:`.Function`
class that is instantiated automatically when called
by name from the :data:`.func` attribute. Note that
calling any name from :data:`.func` has the effect that
a new :class:`.Function` instance is created automatically,
given that name. The primary use case for defining
a :class:`.GenericFunction` class is so that a function
of a particular name may be given a fixed return type.
It can also include custom argument parsing schemes as well
as additional methods.
Subclasses of :class:`.GenericFunction` are automatically
registered under the name of the class. For
example, a user-defined function ``as_utc()`` would
be available immediately::
from sqlalchemy.sql.functions import GenericFunction
from sqlalchemy.types import DateTime
class as_utc(GenericFunction):
type = DateTime
print select([func.as_utc()])
User-defined generic functions can be organized into
packages by specifying the "package" attribute when defining
:class:`.GenericFunction`. Third party libraries
containing many functions may want to use this in order
to avoid name conflicts with other systems. For example,
if our ``as_utc()`` function were part of a package
"time"::
class as_utc(GenericFunction):
type = DateTime
package = "time"
The above function would be available from :data:`.func`
using the package name ``time``::
print select([func.time.as_utc()])
A final option is to allow the function to be accessed
from one name in :data:`.func` but to render as a different name.
The ``identifier`` attribute will override the name used to
access the function as loaded from :data:`.func`, but will retain
the usage of ``name`` as the rendered name::
class GeoBuffer(GenericFunction):
type = Geometry
package = "geo"
name = "ST_Buffer"
identifier = "buffer"
The above function will render as follows::
>>> print func.geo.buffer()
ST_Buffer()
.. versionadded:: 0.8 :class:`.GenericFunction` now supports
automatic registration of new functions as well as package
and custom naming support.
.. versionchanged:: 0.8 The attribute name ``type`` is used
to specify the function's return type at the class level.
Previously, the name ``__return_type__`` was used. This
name is still recognized for backwards-compatibility.
"""
coerce_arguments = True
def __init__(self, *args, **kwargs):
parsed_args = kwargs.pop('_parsed_args', None)
if parsed_args is None:
parsed_args = [_literal_as_binds(c) for c in args]
self.packagenames = []
self._bind = kwargs.get('bind', None)
self.clause_expr = ClauseList(
operator=operators.comma_op,
group_contents=True, *parsed_args).self_group()
self.type = sqltypes.to_instance(
kwargs.pop("type_", None) or getattr(self, 'type', None))
register_function("cast", Cast)
register_function("extract", Extract)
class next_value(GenericFunction):
"""Represent the 'next value', given a :class:`.Sequence`
as its single argument.
Compiles into the appropriate function on each backend,
or will raise NotImplementedError if used on a backend
that does not provide support for sequences.
"""
type = sqltypes.Integer()
name = "next_value"
def __init__(self, seq, **kw):
assert isinstance(seq, schema.Sequence), \
"next_value() accepts a Sequence object as input."
self._bind = kw.get('bind', None)
self.sequence = seq
@property
def _from_objects(self):
return []
class AnsiFunction(GenericFunction):
def __init__(self, **kwargs):
GenericFunction.__init__(self, **kwargs)
class ReturnTypeFromArgs(GenericFunction):
"""Define a function whose return type is the same as its arguments."""
def __init__(self, *args, **kwargs):
args = [_literal_as_binds(c) for c in args]
kwargs.setdefault('type_', _type_from_args(args))
kwargs['_parsed_args'] = args
GenericFunction.__init__(self, *args, **kwargs)
class coalesce(ReturnTypeFromArgs):
pass
class max(ReturnTypeFromArgs):
pass
class min(ReturnTypeFromArgs):
pass
class sum(ReturnTypeFromArgs):
pass
class now(GenericFunction):
type = sqltypes.DateTime
class concat(GenericFunction):
type = sqltypes.String
class char_length(GenericFunction):
type = sqltypes.Integer
def __init__(self, arg, **kwargs):
GenericFunction.__init__(self, arg, **kwargs)
class random(GenericFunction):
pass
class count(GenericFunction):
"""The ANSI COUNT aggregate function. With no arguments,
emits COUNT \*.
"""
type = sqltypes.Integer
def __init__(self, expression=None, **kwargs):
if expression is None:
expression = literal_column('*')
GenericFunction.__init__(self, expression, **kwargs)
class current_date(AnsiFunction):
type = sqltypes.Date
class current_time(AnsiFunction):
type = sqltypes.Time
class current_timestamp(AnsiFunction):
type = sqltypes.DateTime
class current_user(AnsiFunction):
type = sqltypes.String
class localtime(AnsiFunction):
type = sqltypes.DateTime
class localtimestamp(AnsiFunction):
type = sqltypes.DateTime
class session_user(AnsiFunction):
type = sqltypes.String
class sysdate(AnsiFunction):
type = sqltypes.DateTime
class user(AnsiFunction):
type = sqltypes.String
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