capsul-flask/capsulflask/db.py

import psycopg2
import re
import sys
from urllib.parse import urlparse
from os import listdir
from os.path import isfile, join
from psycopg2 import pool
from flask import current_app
from flask import g

from capsulflask.db_model import DBModel

def init_app(app):
  databaseUrl = urlparse(app.config['DATABASE_URL'])

  app.config['PSYCOPG2_CONNECTION_POOL'] = psycopg2.pool.SimpleConnectionPool(
    1, 
    20,
    user = databaseUrl.username,
    password = databaseUrl.password,
    host = databaseUrl.hostname,
    port = databaseUrl.port,
    database = databaseUrl.path[1:]
  )

  schemaMigrations = {}
  schemaMigrationsPath = join(app.root_path, 'schema_migrations')
  print("loading schema migration scripts from {}".format(schemaMigrationsPath))
  for filename in listdir(schemaMigrationsPath):
    key = re.search(r"^\d+_(up|down)", filename).group()
    with open(join(schemaMigrationsPath, filename), 'rb') as file:
      schemaMigrations[key] = file.read().decode("utf8")
  
  connection = app.config['PSYCOPG2_CONNECTION_POOL'].getconn()

  hasSchemaVersionTable = False
  actionWasTaken = False
  schemaVersion = 0
  desiredSchemaVersion = 2

  cursor = connection.cursor()

  cursor.execute("""
    SELECT table_name, table_schema FROM information_schema.tables WHERE table_schema = '{}'
  """.format(app.config['DATABASE_SCHEMA']))

  rows = cursor.fetchall()
  for row in rows:
    if row[0] == "schemaversion":
      hasSchemaVersionTable = True

  if hasSchemaVersionTable == False:
    print("no table named schemaversion found in the {} schema. running migration 01_up".format(app.config['DATABASE_SCHEMA']))
    try:
      cursor.execute(schemaMigrations["01_up"])
      connection.commit()
    except:
      print("unable to create the schemaversion table because: {}".format(my_exec_info_message(sys.exc_info())))
      exit(1)
    actionWasTaken = True

  cursor.execute("SELECT Version FROM schemaversion")
  schemaVersion = cursor.fetchall()[0][0]

  if schemaVersion > desiredSchemaVersion:
    print("schemaVersion ({}) > desiredSchemaVersion ({}). schema downgrades are not supported yet. exiting.".format(
      schemaVersion, desiredSchemaVersion
    ))
    exit(1)

  while schemaVersion < desiredSchemaVersion:
    migrationKey = "%02d_up" % (schemaVersion+1)
    print("schemaVersion ({}) < desiredSchemaVersion ({}). running migration {}".format(
      schemaVersion, desiredSchemaVersion, migrationKey
    ))
    try:
      cursor.execute(schemaMigrations[migrationKey])
      connection.commit()
    except KeyError:
      print("missing schema migration script: {}_xyz.sql".format(migrationKey))
      exit(1)
    except:
      print("unable to execute the schema migration {} because: {}".format(migrationKey, my_exec_info_message(sys.exc_info())))
      exit(1)
    actionWasTaken = True

    schemaVersion += 1
    cursor.execute("SELECT Version FROM schemaversion")
    versionFromDatabase = cursor.fetchall()[0][0]

    if schemaVersion != versionFromDatabase:
      print("incorrect schema version value \"{}\" after running migration {}, expected \"{}\". exiting.".format(
        versionFromDatabase,
        migrationKey, 
        schemaVersion
      ))
      exit(1)
  
  cursor.close()

  app.config['PSYCOPG2_CONNECTION_POOL'].putconn(connection)

  print("{} current schemaVersion: \"{}\"".format(
    ("schema migration completed." if actionWasTaken else "schema is already up to date. "), schemaVersion
  ))

  app.teardown_appcontext(close_db)


def get_model():
    if 'model' not in g:
        connection = current_app.config['PSYCOPG2_CONNECTION_POOL'].getconn()
        cursor = connection.cursor()
        g.db_model = DBModel(connection, cursor)
    return g.db_model


def close_db(e=None):
  model = g.pop("model", None)

  if model is not None:
    model.cursor.close()
    current_app.config['PSYCOPG2_CONNECTION_POOL'].putconn(model.connection)

def my_exec_info_message(exec_info):
  return "{}: {}".format(".".join([exec_info[0].__module__, exec_info[0].__name__]), exec_info[1])