On Wed, Mar 18, 2020, at 1:23 PM, Soumaya Mauthoor wrote:
> Hello
>
> I have two uses cases:
>
> (1) drop cascade as option
> I know I can use custom compilation to add cascade for postgres databases
> using this example:
> https://stackoverflow.com/questions/38678336/sqlalchemy-how-to-implement-drop-table-cascade
> Is it possible to use custom compilation to add cascade as an optional
> keyword argument to drop()?
drop() doesn't accept any optional keyword arguments so you're best off making
your own subclass of DropTable called DropTableCascade and just executing it:
conn.execute(DropTableCascade(mytable))
>
> (2) overwriting func functions
> Is it possible to overwrite func.greatest to return func.max for SQLite?
generic functions are used for this. Since "max" is a multiple-typed function
you can use a helper class called ReturnTypeFromArgs:
from sqlalchemy.sql.functions import ReturnTypeFromArgs
from sqlalchemy.ext.compiler import compiles
from sqlalchemy.sql import literal_column
from sqlalchemy.sql import func
from sqlalchemy.dialects import sqlite
class greatest(ReturnTypeFromArgs):
pass
@compiles(greatest, "sqlite")
def _render_max(elem, compiler, **kw):
return "max(%s)" % compiler.process(elem.clauses)
print(func.greatest(literal_column("foo")))
print(func.greatest(literal_column("foo")).compile(dialect=sqlite.dialect()))
>
> I'm trying to learn more about custom compilation in general. This page is
> very helpful:
> http://docs.sqlalchemy.org/en/latest/core/compiler.html
>
> Are there other resources you recommend?
>
> Soumaya
>
>
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> SQLAlchemy -
> The Python SQL Toolkit and Object Relational Mapper
>
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SQLAlchemy -
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http://www.sqlalchemy.org/
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