Tuesday, December 28, 2010

Activation/Deactivation of python virtualenv upon entering a directory

It's not a new or original idea – I've heard about it from Dmitry Gladkov but as usual didn't remember details. So, I've created my own implementation of activation/deactivation of python virtualenv:



  if [ "$PWD" != "$PREVPWD" ]; then
    if [ -n "$PREVENV_PATH" ]; then
      if [ "`echo "$PWD" | grep -c $PREVENV_PATH`" = "0"  ]; then
         source $PREVENV_PATH/.venv
         echo "> Virtualenv `basename $VIRTUALENV_PATH` deactivated"
    # activate virtualenv dynamically
    if [ -e "$PWD/.venv" ] && [ "$PWD" != "$PREVENV_PATH" ]; then
      source $PWD/.venv
      source $VIRTUALENV_PATH/bin/activate
      echo "> Virtualenv `basename $VIRTUALENV_PATH` activated"

export PROMPT_COMMAND=handle_virtualenv
Just paste this code into your
and place
file with declaration like below:
And it should works like a charm. Script only for bash!

Thursday, December 23, 2010

Django model migrations with South: how-to migrate ForeignKey relation to ManyToMany

Yesterday I had an non-trivial for newbie South user issue: I need to migrate a big database table with existing FK relations to M2M relations and keep in safety all of existing data during migration.

So, I hadn't figure out in documentation how I can do it without handmade migration code in forward method. Below I described how I've fixed it:

1. Here is my initial model (sample), my application called app1
class TestData(models.Model):
    field1 = models.CharField(max_length=200)
    field2 = models.CharField(max_length=200)

class Knight(models.Model):
    name = models.CharField(max_length=100)
    additional_field_new_name = models.CharField(\
        max_length=155, default='')
    data = models.ForeignKey(TestData)

2. I've added new column data_new to Knight model with M2M relation to TestData:
data_new = models.ManyToManyField(TestData, \

3. Start schema migration:
python manage.py schemamigration app1 --auto

4. Change forward method in our new migration, code after creation of new column/proxy model:
for obj in orm.Knight.objects.all():

5. Make migration:
python manage.py migrate app1

6. Remove column data from model and make migration; rename m2m column data_new to data and start schema migration
# remove column "data" from model
python manage.py schemamigration app1 --auto
python manage.py migrate app1

# rename m2m column from "data_new" to "data"
python manage.py schemamigration app1 --auto

7. At this point I need to keep all existing data in proxy table but South won't do that for me. So, I need to change forward method of migration (actually I need to replace generated code to following):
db.delete_unique('app1_knight_data_new', ['knight_id', 'testdata_id'])

db.rename_table('app1_knight_data_new', 'app1_knight_data')
db.create_unique('app1_knight_data', ['knight_id', 'testdata_id'])

Update: for Postgres (and I assume for MySQL with InnoDB db storage too) order of above commands is important: you have to delete old unique constraint before renaming of the proxy table.

8. After that just make migration:
python manage.py migrate app1

So, we've done and everything in safety.

Friday, December 17, 2010

Keep synced production media files with your development environment- the "dirty" way

As I wrote in previous post, it's really problem personally for me to keep synced media between dev and production environment. I don't examine cases when on production available really a lot of data.

Copy user-related media files – usually solved via ignore files, symlinks etc. but there is NO STANDARD or SOLUTION - Unsolved
Quick and dirty solution:
# 1) go to parent folder of your 
# static_media (usually project's root folder)

# 2) execute
rsync -avzu -e ssh mylogin@remotehost:~/path/to/static_media ./

 And execute it every time you need have synced media files with your remote host. 

 I've hacked previous version of script to exclude files which already in git repo.
rsync -avzu echo `git ls-files | \
   grep static/ | \
   xargs -I file echo --exclude="file"` \
   -e ssh mylogin@remotehost:~/path/to/static_media ./