How to check if PostgreSQL schema exists using SQLAlchemy?

Question

I am using SQLAlchemy to generate tables in a specific schema in a PostgreSQL database. If the schema does not exist, I want to create it. I know the PostgreSQL query to che

Answer 1

I've been using this with Postgres, though was surprised to learn that IF NOT EXISTS is not part of the SQL standard -

engine.execute('CREATE SCHEMA IF NOT EXISTS foo;')

Apparently it's an extension for Postgres and MySQL - https://www.w3resource.com/sql/sql-basic/create-schema.php

Answer 2

This worked for me. Finds if a schema exists using pure SqlAlchemy:

from sqlalchemy import create_engine
from sqlalchemy import event
from sqlalchemy.schema import CreateSchema, DropSchema
...
engine = create_engine(dbstr)
meta = ModelBase()
...
if not engine.dialect.has_schema(engine, schema=schema_name):
    event.listen(meta.metadata, 'before_create', CreateSchema(schema_name))

meta.metadata.reflect(bind=engine, schema=schema_name)
meta.metadata.create_all(engine, checkfirst=True)

Answer 3

@javax's answer is almost correct; the following is a little clarification:

q = exists(select([("schema_name")]).select_from("information_schema.schemata")
    .where("schema_name = 'foo'"))
if not session.query(q).scalar():
    session.execute('CREATE SCHEMA foo;')

Answer 4

If you want to integrate it with SQLAlchemy you could use reflection but for an easier and quicker solution:

from sqlalchemy.sql import exists, select
exists(select([("schema_name")]).select_from("information_schema.schemata").
       where("schema_name == 'foo'"))

This will return True or False.