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A database driver for Django to connect to an Informix db via ODBC

Project description

A database driver for Django to connect to an Informix database via pyodbc.

Some limitations:

  • Does not support default values
  • Informix automatically creates indexes on foreign keys, but Django attempts to do that manually; the current implementation here just attempts to catch the error on index creation. It may unintentionally catch other index creation errors where the index already exists.

Configure local environment

The following environment variables should exist:

INFORMIXDIR
The path to the Informix client install directory
INFORMIXSERVER
The name of the Informix service to which we need to connect
INFORMIXSQLHOSTS
The path to the sqlhosts file that the Informix driver should use
LD_LIBRARY_PATH
The path(s) to the various Informix library files: Usually $INFORIMIXDIR/lib:$INFORMIXDIR/lib/cli:$IMFORMIXDIR/lib/esql
DB_LOCALE
In case of Database locale information mismatch. error during connection, you should specify your database locale, e.g. DB_LOCALE=en_US.8859-15

You will also need to add an entry within your sqlhosts file for each remote/local Informix server connection in the following format:

<INFORMIX_SERVER_NAME>    onsoctcp     <INFORMIX_HOST_NAME>    <INFORMIX_SERVICE_NAME>

For example:

dev    onsoctcp    localhost    9088

You may alternatively use a symbolic name in that line in place of the port number, typically sqlexec and then configure the port number in the /etc/services file:

sqlexec    9088/tcp

Configure settings.py

Django’s settings.py uses the following to connect to an Informix database:

'default': {
    'ENGINE': 'django_informixdb',
    'NAME': 'myproject',
    'SERVER': 'ifxserver',
    'USER' : 'testuser',
    'PASSWORD': 'passw0rd',
    'OPTIONS': {
        'DRIVER': '/path/to/iclit09b.so'. # Or iclit09b.dylib on macOS
        'CPTIMEOUT': 120,
        'CONN_TIMEOUT': 120,
        'ISOLATION_LEVEL': 'READ_UNCOMMITTED',
        'LOCK_MODE_WAIT': 0,
        'VALIDATE_CONNECTION': True,
    },
    'CONNECTION_RETRY': {
        'MAX_ATTEMPTS': 10,
    },
    'TEST': {
        'NAME': 'myproject',
        'CREATE_DB': False
    }
}
CPTIMEOUT

This will set connection pooling timeout. Possible values:

0 - Turn off connection pooling
nn - timeout set nn seconds
CONN_TIMEOUT

This will set timeout for operations on connections (connection, ??closing??, we’re not sure). Possible values:

0 - Default timeout to the database (which could mean no timeout)
nn - timeout set nn seconds
ISOLATION_LEVEL

This will set database isolation level at connection level Possible values:

READ_COMMITED
READ_UNCOMMITTED
SERIALIZABLE
LOCK_MODE_WAIT

This will set database LOCK MODE WAIT at connection level Application can use this property to override the default server process for accessing a locked row or table. The default value is 0 (do not wait for the lock). Possible values:

-1 - WAIT until the lock is released.
0 - DO NOT WAIT, end the operation, and return with error.
nn - WAIT for nn seconds for the lock to be released.
VALIDATE_CONNECTION
Whether existing connections should be validated at the start of the request. Defaults to False.
VALIDATION_INTERVAL
How often in seconds to revalidate connections if VALIDATE_CONNECTION is enabled. Defaults to 300 (5 minutes).
VALIDATION_QUERY
Query used to validate whether a connection is usable. Defaults to “SELECT 1 FROM sysmaster:sysdual”.
CONNECTION_RETRY

When opening a new connection to the database, automatically retry up to MAX_ATTEMPTS times in the case of errors. Only error codes in ERRORS will trigger a retry. The wait time between retries is calculated using an exponential backoff with jitter formula:

random_between(WAIT_MIN, min(WAIT_MAX, WAIT_MULTIPLIER * WAIT_EXP_BASE ** (attempt - 1)))

Defaults (wait times are in milliseconds):

MAX_ATTEMPTS: 1  # this implies no retries
WAIT_MIN: 0
WAIT_MAX: 1000
WAIT_MULTIPLIER: 25
WAIT_EXP_BASE: 2
ERRORS: ['-908', '-930', '-27001']

Each of these settings can be overridden in the CONNECTION_RETRY section of the database configuration in settings.py. For example:

DATABASES = {
   'default': {
       'ENGINE': 'django_informixdb',
       'CONNECTION_RETRY': {
           'MAX_ATTEMPTS': 10,
           'WAIT_MIN': 0,
           'WAIT_MAX': 500,
       },
       # ...
    },
 }

The error codes that are retried by default correspond to the following errors:

  • -908 Attempt to connect to database server (servername) failed
  • -930 Cannot connect to database server servername
  • -27001 Read error occurred during connection attempt

These errors are often seen when the database server is too busy, too many clients are attempting to connect at the same time or a network firewall has chopped the connection.

Using with the Docker Informix Dev Database

The docker image from IBM for the Informix developer database image behaves a little differently compared to other images. As such it needs a little extra handling, and doesn’t seem to work with docker-compose

Firstly we need to download and getting it running:

$ docker run -itd --name iif_developer_edition --privileged -p 9088:9088 -p 9089:9089 -p 27017:27017 \
-p 27018:27018 -p 27883:27883 -e LICENSE=accept ibmcom/informix-developer-database:latest

This will download the image if it doesn’t exist, and then run it with the name iif_developer_edition. The first time this run, the image will do a bunch of initial setup stuff. As we used the -d option, it will run in the background as a detached process. So don’t be concerned that you do not see anything in the output.

You can stop and restart the container with:

$ docker stop iif_developer_edition
$ docker start iif_developer_edition

It seems that the Informix ODBC driver does not currently support creating databases. So we will need to do that manually, by attaching to the running container

$ docker attach iif_developer_edition

This will give you a shell on the running container, and you can therefore use dbaccess to create your database. You can exit this shell using Ctrl-p Ctrl-q without shutting down the whole container.

This Django database adaptor for Informix requires transaction support to be enabled in our database. This is not the default within the Informix Developer image. So you need to enable it on a per database basis:

$ docker attach iif_developer_edition
$ ontape -s -B <DB_NAME>

Again, you can detach using Ctrl-p Ctrl-q.

Finally you need to ensure that our local dev database is included in the sqlhosts file. e.g.:

dev    onsoctcp    localhost    9088

You should now be able to point Django to our local test database using the syntax detailed above.

Using Django InformixDB with docker-compose

It is possible to use the Informix developer docker image with docker-compose with a little effort.

Example docker-compose.yml

version: '3'

services:
    db:
        image: ibmcom/informix-developer-database
        tty: true # Needed to ensure container doesn't self terminate
        environment:
            LICENSE: accept
        privileged: true
        ports:
            - "9088:9088"
            - "9089:9089"
            - "27017:27017"
            - "27018:27018"
            - "27883:27883"

The key entry in the compose file which is out of the ordinary is tty: true. This allocates a (virtual) TTY to the container. The Informix developer database container expects a tty and terminates without one when run inside docker-compose.

Once it is up and running with docker-compose up you can run a bash shell on the running container with:

docker exec -it informix_db_1 bash

Where informix_db_1 is the name of the running container. From this shell you can create your DB with dbaccess etc.

Warning

This approach still requires the SDK to installed locally and the appropriate environmental variables to be set up. Along with entries in sqlhosts and /etc/services

Testing against an Informix Database

Due to a bug in the Informix ODBC driver, it is not currently possible to run Django tests normally. Specifically, it is not possible for Django to create a test database. As such, you will need to do it manually. By default Django will attempt to create a database with a name equal to the default database name with a test_ prefix. e.g. if you database name is my_database, the test database name would be test_my_database. This can be overridden with the NAME option under TEST.

To prevent Django from attempting to create a test database, set the CREATE_DB option under TEST to False: see ‘Configure settings.py’ above.

You can follow the steps above, in the section on using Informix locally with Docker to create a test database. Then when running the test you can tell Django to re-use an existing database, rather than trying to create a new one with the -k parameter:

./manage.py test -k

For django_informixdb Developers

To run the django_informixdb test suite, you need to set the INFORMIXDIR environment variable, and the tests expect an Informix database at host “informix”. Change that host in test/conftest.py if you need to. Then run the test suite with:

tox

This will run the tests under Django 1 and 2.

Release History

Version 1.9.0

  • Enable setting a validation interval.

Version 1.8.0

  • Enable validating connections at start of request.

Version 1.7.0

  • Add CONN_TIMEOUT setting.

Version 1.5.0

  • Enable retrying if get connection fails.

Version 1.3.3

  • Compability fix for Django 2+ to remove old “context” argument from custom fields

Version 1.3.0

  • Addressing deprecation warning for conversion functions in Django 2+
  • Detect incorrect INFORMIXSQLHOSTS setting earlier for better error message

Version 1.2.0

  • Fix bug in DecimalField handling under Django 2+

Version 1.1.0

  • Added LOCK_MODE_WAIT option

Version 1.0.0

  • Initial public release

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