So, anyway, I must implement BitAnd class? Or I can check if 'element.op ==
&' inside compile function?
чт, 19 апр. 2018 г., 16:31 Mike Bayer <mike...@zzzcomputing.com>:
> On Thu, Apr 19, 2018 at 5:21 AM, Антонио Антуан <a.ch....@gmail.com>
> wrote:
> > Hi guys.
> >
> > Is there any mechanism in SQLAlchemy which allows to redefine operator
> > compilation? I want to the same thing as already exists for functions.
> > An example for functions:
> >
> >
> > class IntDiv(GenericFunction):
> > type = Integer
> > package = 'adc_custom'
> > name = 'div'
> > identifier = 'div'
> >
> >
> > @compiles(IntDiv)
> > def visit_div_default(element, compiler, **kwargs):
> > params = [compiler.process(c.self_group()) for c in
> > element.clause_expr.element.get_children()]
> > return '%s / %s' % (params[0], params[1])
> >
> >
> > @compiles(IntDiv, 'clickhouse')
> > def visit_div_ch(element, compiler, **kwargs):
> > return 'intDiv(%s)' % compiler.process(element.clause_expr.element)
> >
> > What I want to do:
> >
> > class BitAdd(CustomOp):
> > pass
> >
> > @compiles(BitAdd)
> > def visit_bit_add_default(element, compiler, **kwargs):
> > return '%s & %s' % (element.left, element.right)
> >
> >
> > @compiles(IntDiv, 'clickhouse')
> > def visit_bit_add_ch(element, compiler, **kwargs):
> > return 'bitAnd(%s, %s)' % (element.left, element.right)
> >
> > Statement looks like that:
> > some_col.op('&')(some_int_flag)
> >
> >
> > I understand that I can define generic function and use it instead of
> > `.op('&')`, but at first I want to find another way.
>
> So in this case you are looking to override the compilation for
> BinaryElement in any case since you want to run a function around them
> in one case, that is the whole left/operator/right object.
>
> from sqlalchemy.sql.expression import BinaryExpression
> @compiles(BinaryExpression, "clickhouse")
> def visit_binary(element, compiler, **kw):
> if isinstance(element.operator, BitAdd):
> return "bitAnd(%s, %s)" % (compiler.process(element.left,
> **kw), compiler.process(element.right, **kw))
> else:
> return compiler.visit_binary(element, **kw)
>
> For the part where you want op('&') to be magic, it can't work that
> way, though you can get at the '&' operator directly but you normally
> need to use a subclass of Integer:
>
>
> http://docs.sqlalchemy.org/en/latest/core/custom_types.html#redefining-and-creating-new-operators
>
> so here you'd be saying:
>
> from sqlalchemy import Integer
>
> class MyInt(Integer):
> class comparator_factory(Integer.Comparator):
> def __and__(self, other):
> return BitAnd()(self.expr, other)
>
> then you'd use the MyInt datatype in your mappings where you want your
> special operator to take place.
>
> If you want the base Integer to do this, you'd need to monkeypatch the
> comparator, this is less recommended as it can cause surprises:
>
>
> class comparator_factory_mixin(object):
> def __and__(self, other):
> return BitAnd()(self.expr, other)
>
> Integer.Comparator.__bases__ = (comparator_factory_mixin, ) +
> Integer.Comparator.__bases__
>
>
>
>
>
> > --
> > SQLAlchemy -
> > The Python SQL Toolkit and Object Relational Mapper
> >
> > http://www.sqlalchemy.org/
> >
> > To post example code, please provide an MCVE: Minimal, Complete, and
> > Verifiable Example. See http://stackoverflow.com/help/mcve for a full
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> --
> SQLAlchemy -
> The Python SQL Toolkit and Object Relational Mapper
>
> http://www.sqlalchemy.org/
>
> To post example code, please provide an MCVE: Minimal, Complete, and
> Verifiable Example. See http://stackoverflow.com/help/mcve for a full
> description.
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--
Антон
--
SQLAlchemy -
The Python SQL Toolkit and Object Relational Mapper
http://www.sqlalchemy.org/
To post example code, please provide an MCVE: Minimal, Complete, and Verifiable
Example. See http://stackoverflow.com/help/mcve for a full description.
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