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I have a function which returns json data as history from Version of reversion.models.

from django.http import HttpResponse
from reversion.models import Version
from django.contrib.admin.models import LogEntry
import json
def history_list(request):
    history_list = Version.objects.all().order_by('-revision__date_created')
    data = []
    for i in history_list:
        data.append({
            'date_time': str(i.revision.date_created),
            'user': str(i.revision.user),
            'object': i.object_repr,
            'field': i.revision.comment.split(' ')[-1],
            'new_value_field': str(i.field_dict),
            'type': i.content_type.name,
            'comment': i.revision.comment
        })

    data_ser = json.dumps(data)
    return HttpResponse(data_ser, content_type="application/json")

When I run the above snippet I get the output json as 

[{"type": "fruits", "field": "colour", "object": "anyobject", "user": "anyuser", "new_value_field": "{'price': $23, 'weight': 2kgs, 'colour': 'red'}", "comment": "Changed colour."}]

From the function above,

'comment': i.revision.comment

returns json as "comment": "changed colour" and colour is the field which I have written in the function to retrieve it from comment as

'field': i.revision.comment.split(' ')[-1]

But i assume getting fieldname and value from field_dict is a better approach

Problem: from the above json list I would like to filter new_field_value and old_value. In the new_filed_value only value of colour.

Praneeth
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1 Answers1

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Getting the changed fields isn't as easy as checking the comment, as this can be overridden.

Django-reversion just takes care of storing each version, not comparing.

Your best option is to look at the django-reversion-compare module and its admin.py code.

The majority of the code in there is designed to produce a neat side-by-side HTML diff page, but the code should be able to be re-purposed to generate a list of changed fields per object (as there can be more than one changed field per version).

The code should* include a view independent way to get the changed fields at some point, but this should get you started:

from reversion_compare.admin import CompareObjects
from reversion.revisions import default_revision_manager

def changed_fields(obj, version1, version2):
    """
    Create a generic html diff from the obj between version1 and version2:
        A diff of every changes field values.
    This method should be overwritten, to create a nice diff view
    coordinated with the model.
    """
    diff = []

    # Create a list of all normal fields and append many-to-many fields
    fields = [field for field in obj._meta.fields]
    concrete_model = obj._meta.concrete_model
    fields += concrete_model._meta.many_to_many

    # This gathers the related reverse ForeignKey fields, so we can do ManyToOne compares
    reverse_fields = []
    # From: http://stackoverflow.com/questions/19512187/django-list-all-reverse-relations-of-a-model
    changed_fields = []
    for field_name in obj._meta.get_all_field_names():
        f = getattr(
            obj._meta.get_field_by_name(field_name)[0],
            'field',
            None
        )
        if isinstance(f, models.ForeignKey) and f not in fields:
            reverse_fields.append(f.rel)

    fields += reverse_fields

    for field in fields:
        try:
            field_name = field.name
        except:
            # is a reverse FK field
            field_name = field.field_name

        is_reversed = field in reverse_fields
        obj_compare = CompareObjects(field, field_name, obj, version1, version2, default_revision_manager, is_reversed)

        if obj_compare.changed():
            changed_fields.append(field)

    return changed_fields

This can then be called like so:

changed_fields(MyModel,history_list_item1, history_list_item2)

Where history_list_item1 and history_list_item2 correspond to various actual Version items.

*: Said as a contributor, I'll get right on it.

Community
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