Merge pull request #8 from jackton1/feature/add-create-copy-of-instan…

…ce-utility

Added create_copy_of_instance utility.

README.md

@@ -86,6 +86,39 @@ In [10]: clone.tags.all()
 Out[10]: <QuerySet [<Tag: men>, <Tag: women>]>
 ```
 
+### Creative clones without using `CloneMixin`.
+
+> NOTE: This method won't copy over related objects like Many to Many/One to Many relationships.
+
+```python
+
+In [1]: from model_clone import create_copy_of_instance
+
+In [2]: test_obj = TestModel.objects.create(title='New')
+
+In [3]: test_obj.tags.create(name='men')
+
+In [4]: test_obj.tags.create(name='women')
+
+In [5]: clone = create_copy_of_instance(test_obj, attrs={'title': 'Updated title'})
+
+In [6]: test_obj.pk
+Out[6]: 1
+
+In [7]: test_obj.title
+Out[7]: 'New'
+
+In [8]: test_obj.tags.all()
+Out[8]: <QuerySet [<Tag: men>, <Tag: women>]>
+
+In [9]: clone.pk
+Out[9]: 2
+
+In [10]: clone.title
+Out[10]: 'Updated title'
+
+In [11]: clone.tags.all()
+Out[11]: <QuerySet []>
 
 ### Duplicating Models from Django Admin view.
 

model_clone/__init__.py

@@ -1,4 +1,5 @@
 from .mixins import CloneMixin  # noqa
+from .utils import create_copy_of_instance  # noqa
 from .admin import ClonableModelAdmin  # noqa
 
-__all__ = ['CloneMixin', 'ClonableModelAdmin']
+__all__ = ['CloneMixin', 'ClonableModelAdmin', 'create_copy_of_instance']

model_clone/utils.py

@@ -0,0 +1,76 @@
+from django.core.exceptions import ValidationError
+from django.db import models
+
+
+def create_copy_of_instance(instance, exclude=(), save_new=True, attrs=()):
+    """
+    Clone an instance of `django.db.models.Model`.
+
+    Args:
+        instance(django.db.models.Model): The model instance to clone.
+        exclude(list|set): List or set of fields to exclude from unique validation.
+        **attrs: Kwargs of field and value to set on the duplicated instance.
+
+    Returns:
+        (django.db.models.Model): The new duplicated instance.
+
+    Examples:
+        >>> from django.contrib.auth import get_user_model
+        >>> from sample.models import Book
+        >>> user = get_user_model().objects.create()
+        >>> instance = Book.objects.get(pk=1)
+        >>> instance.pk
+        1
+        >>> instance.name
+        "The Beautiful Life"
+        >>> duplicate.pk
+        2
+        >>> duplicate.name
+        "Duplicate Book 2"
+    """
+
+    defaults = {}
+    attrs = attrs or {}
+    fields = instance.__class__._meta.concrete_fields
+
+    if not isinstance(instance, models.Model):
+        raise ValueError('Invalid: Expected an instance of django.db.models.Model')
+
+    if not isinstance(attrs, dict):
+        try:
+            attrs = dict(attrs)
+        except (TypeError, ValueError):
+            raise ValueError('Invalid: Expected attrs to be a dict or iterable.')
+
+    for f in fields:
+        if all([
+            not f.auto_created,
+            f.concrete,
+            f.editable,
+            f not in instance.__class__._meta.related_objects,
+            f not in instance.__class__._meta.many_to_many,
+        ]):
+            defaults[f.attname] = getattr(instance, f.attname, f.get_default())
+    defaults.update(attrs)
+
+    new_obj = instance.__class__(**defaults)
+
+    exclude = exclude or [
+        f.name for f in instance._meta.fields
+        if any([
+            f.name not in defaults,
+            f.has_default(),
+            f.null,
+        ])
+    ]
+
+    try:
+        # Run the unique validation before creating the instance.
+        new_obj.full_clean(exclude=exclude)
+    except ValidationError as e:
+        raise ValidationError(', '.join(e.messages))
+
+    if save_new:
+        new_obj.save()
+
+    return new_obj