API¶

Forms ¶

ConcurrentForm ¶

class concurrency.forms.ConcurrentForm(data=None, files=None, auto_id='id_%s', prefix=None, initial=None, error_class=<class 'django.forms.utils.ErrorList'>, label_suffix=None, empty_permitted=False, instance=None, use_required_attribute=None, renderer=None)[source]¶

Simple wrapper to ModelForm that try to mitigate some concurrency error.

Note that is always possible have a RecordModifiedError in model.save(). Statistically form.clean() should catch most of the concurrent editing, but is good to catch RecordModifiedError in the view too.

VersionWidget ¶

class concurrency.forms.VersionWidget(attrs=None)[source]¶

Widget that show the revision number using <div>.

Usually VersionField use HiddenInput as Widget to minimize the impact on the forms, in the Admin this produce a side effect to have the label Version without any value, you should use this widget to display the current revision number

Exceptions ¶

VersionChangedError ¶

class concurrency.exceptions.VersionChangedError(message, code=None, params=None)[source]¶

class concurrency.exceptions.RecordModifiedError¶

RecordModifiedError ¶

class concurrency.exceptions.RecordModifiedError(*args, **kwargs)[source]¶

InconsistencyError ¶

Changed in version 0.7.

Warning

removed in 0.7

class concurrency.exceptions.InconsistencyError¶

VersionError ¶

class concurrency.exceptions.VersionError(message=None, code=None, params=None, *args, **kwargs)[source]¶

Admin ¶

ConcurrentModelAdmin ¶

class concurrency.admin.ConcurrentModelAdmin(model, admin_site)[source]¶

Warning

If you customize fields or fieldsets remember to add version field to the list. (See issue issue #81)

ConcurrencyActionMixin ¶

class concurrency.admin.ConcurrencyActionMixin[source]¶

ConcurrencyListEditableMixin ¶

class concurrency.admin.ConcurrencyListEditableMixin[source]¶

Middleware ¶

class concurrency.middleware.ConcurrencyMiddleware¶

ConcurrencyMiddleware ¶

concurrency.views.conflict ¶

concurrency.views.conflict(request, target=None, template_name='409.html')[source]¶

409 error handler.

Parameters:

request – Request
template_name – 409.html
target – The model to save

Helpers ¶

apply_concurrency_check()¶

Added in version 0.4.

Changed in version 0.8.

Add concurrency check to existing classes.

Note

With Django 1.7 and the new migrations management, this utility does not work anymore. To add concurrency management to a external Model, you need to use a migration to add a VersionField to the desired Model.

Note

See demo.auth_migrations for a example how to add IntegerVersionField to auth.Group )

operations = [
    # add version to django.contrib.auth.Group
    migrations.AddField(
        model_name='Group',
        name='version',
        field=IntegerVersionField(help_text=b'Version', default=1),
    ),
]

and put in your settings.py

MIGRATION_MODULES = {
    ...
    ...
    'auth': '<new.migration.package>',
}

disable_concurrency()¶

Added in version 0.6.

Context manager to temporary disable concurrency checking.

Changed in version 0.9.

Starting from version 0.9, disable_concurrency can disable both at Model level or instance level, depending on the passed object. Passing Model is useful in django commands, load data or fixtures, where instance should be used by default

Changed in version 1.0.

Is now possible use disable_concurrency without any argument to disable concurrency on any Model. This features has been developed to be used in django commands

Changed in version 1.1.

Does not raise an exception if a model not under concurrency management is passed as argument.

examples ¶

@disable_concurrency()
def recover_view(self, request, version_id, extra_context=None):
    return super().recover_view(request,
                                                        version_id,
                                                        extra_context)

def test_recover():
    deleted_list = revisions.get_deleted(ReversionConcurrentModel)
    delete_version = deleted_list.get(id=5)

    with disable_concurrency(ReversionConcurrentModel):
        deleted_version.revert()

concurrency_disable_increment()¶

Added in version 1.1.

Context manager to temporary disable version increment. Concurrent save is still checked but no version increment is triggered, this creates ‘shadow saves’,

It accepts both a Model or an instance as target.

Templatetags ¶

identity ¶

concurrency.templatetags.concurrency.identity(obj)[source]¶: Return a string representing “<pk>,<version>” of the passed object.

version ¶

concurrency.templatetags.concurrency.version(obj)[source]¶: Return the value of the VersionField of the passed object.

is_version ¶

concurrency.templatetags.concurrency.is_version(field)[source]¶: Return True if passed argument is a VersionField instance.

Triggers ¶

TriggerFactory ¶

Added in version 2.3.

class concurrency.triggers.TriggerFactory(connection)[source]¶

Abstract Factory class to create triggers.

Implemementations need to set the following attributes

update_clause, drop_clause and list_clause

Those will be formatted using standard python format() as:

self.update_clause.format(trigger_name=field.trigger_name,
                                   opts=field.model._meta,
                                   field=field)

So as example:

update_clause =  """CREATE TRIGGER {trigger_name}
            AFTER UPDATE ON {opts.db_table}
            BEGIN UPDATE {opts.db_table}
            SET {field.column} = {field.column}+1
            WHERE {opts.pk.column} = NEW.{opts.pk.column};
            END;
            """

VersionField is ‘displayed’ in the Form using an django.forms.HiddenInput widget, anyway to be sure that the version is not tampered with, its value is signed. The default VersionSigner is concurrency.forms.VersionFieldSigner that simply extends django.core.signing.Signer. If you want change your Signer you can set CONCURRENCY_FIELD_SIGNER in your settings

mysigner.py

class DummySigner():
    """ Dummy signer that simply returns the raw version value. (Simply do not sign it) """
    def sign(self, value):
        return smart_str(value)

    def unsign(self, signed_value):
        return smart_str(signed_value)

settings.py

CONCURRENCY_FIELD_SIGNER = "myapp.mysigner.DummySigner"