util.py

import sqlalchemy as sa
from sqlalchemy.ext import compiler
from sqlalchemy.schema import DDLElement
from sqlalchemy.sql import table

# This is based on https://github.com/sqlalchemy/sqlalchemy/wiki/Views


class CreateView(DDLElement):
    def __init__(self, name, selectable):
        self.name = name
        self.selectable = selectable


class DropView(DDLElement):
    def __init__(self, name):
        self.name = name


@compiler.compiles(CreateView)
def _create_view(element, compiler, **kw):
    return 'CREATE VIEW %s AS %s' % (
        element.name,
        compiler.sql_compiler.process(element.selectable, literal_binds=True),
    )


@compiler.compiles(DropView)
def _drop_view(element, compiler, **kw):
    return 'DROP VIEW %s' % (element.name)


def view_exists(ddl, target, connection, **kw):
    return ddl.name in sa.inspect(connection).get_view_names()


def view_doesnt_exist(ddl, target, connection, **kw):
    return not view_exists(ddl, target, connection, **kw)


def view(name, metadata, selectable):
    t = table(name)

    t._columns._populate_separate_keys(
        col._make_proxy(t, primary_key=set(), foreign_keys=set()) for col in selectable.selected_columns
    )

    sa.event.listen(
        metadata,
        'after_create',
        CreateView(name, selectable).execute_if(callable_=view_doesnt_exist),
    )
    sa.event.listen(metadata, 'before_drop', DropView(name).execute_if(callable_=view_exists))
    return t