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# This file is part of daf_butler. 

# 

# Developed for the LSST Data Management System. 

# This product includes software developed by the LSST Project 

# (http://www.lsst.org). 

# See the COPYRIGHT file at the top-level directory of this distribution 

# for details of code ownership. 

# 

# This program is free software: you can redistribute it and/or modify 

# it under the terms of the GNU General Public License as published by 

# the Free Software Foundation, either version 3 of the License, or 

# (at your option) any later version. 

# 

# This program is distributed in the hope that it will be useful, 

# but WITHOUT ANY WARRANTY; without even the implied warranty of 

# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 

# GNU General Public License for more details. 

# 

# You should have received a copy of the GNU General Public License 

# along with this program. If not, see <http://www.gnu.org/licenses/>. 

 

__all__ = ("View", ) 

 

from sqlalchemy import MetaData 

from sqlalchemy.schema import DDLElement 

from sqlalchemy.sql import text, select, TableClause 

from sqlalchemy.ext import compiler 

from sqlalchemy import event 

 

 

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 compileCreateView(element, compiler, **kw): 

return "CREATE VIEW IF NOT EXISTS %s AS %s" % (element.name, 

compiler.sql_compiler.process(element.selectable)) 

 

 

# Ignoring PEP8 redefinition of function, as this is the sqlalchemy 

# recommended procedure for dealing with multiple dialects 

@compiler.compiles(CreateView, 'oracle') # noqa: F811 

def compileCreateView(element, compiler, **kw): 

# This is special cased as oracle does not support IF NOT EXISTS, 

# but should be kept until the consequences of using CREATE OR REPLACE 

# would be on users who are actively using a view when someone else 

# attempts to create or replace it. 

return """ 

DECLARE 

nCount NUMBER; 

BEGIN 

SELECT COUNT(view_name) INTO nCount FROM user_views WHERE view_name = '{}'; 

IF(nCount <= 0) 

THEN 

execute immediate 'CREATE VIEW {} AS {}'; 

END IF; 

END; 

""".format(element.name, 

element.name, 

compiler.sql_compiler.process(element.selectable).replace(";\n FROM DUAL", "")) 

 

 

@compiler.compiles(DropView) 

def compileDropView(element, compiler, **kw): 

return "DROP VIEW %s" % (element.name) 

 

 

class View(TableClause): 

"""Make a SQL view. 

 

Parameters 

---------- 

name : `str` 

Name of the view table. 

metadata : `sqlalchemy.Metadata` 

Metadata to attach the view to. 

selectable : `sqlalchemy.sql.select` or `str` 

The SQL ``SELECT`` clause used to generate the view. 

comment : `str`, optional 

Text description of the view. Unlike the comment attribute of 

actual `sqlalchemy.schema.SchemaItem` instances, this comment is 

not currently used when creating the view, but it may be in the 

future. 

info : `dict`, optional 

Arbitrary extra information describing the view. 

""" 

 

def __init__(self, name, metadata, selectable, comment=None, info=None): 

super().__init__(name) 

self.comment = comment 

self.info = info 

 

if isinstance(selectable, str): 

selectable = select([text(selectable.lstrip("SELECT"))]) 

 

for c in selectable.c: 

c._make_proxy(self) 

 

@event.listens_for(MetaData, "after_create") 

def receive_after_create(target, connection, **kwargs): 

connection.execute(CreateView(name, selectable)) 

 

@event.listens_for(MetaData, "before_drop") 

def receive_before_drop(target, connection, **kwargs): 

connection.execute(DropView(name))