V2: Add merge props (#60)

* Add merge props

* add docs

README.md

@@ -183,6 +183,34 @@ def example(request):
 
 In the example above, the `data1`, and `data2` props will be fetched in one request, while the `data` prop will be fetched in a separate request in parallel. Group names are arbitrary strings and can be anything you choose.
 
+### Merge Props
+
+By default, Inertia overwrites props with the same name when reloading a page. However, there are instances, such as pagination or infinite scrolling, where that is not the desired behavior. In these cases, you can merge props instead of overwriting them.
+
+```python
+from inertia import merge, inertia
+
+@inertia('ExampleComponent')
+def example(request):
+  return {
+    'name': lambda: 'Brandon', 
+    'data': merge(Paginator(objects, 3)), 
+  }
+```
+
+You can also combine deferred props with mergeable props to defer the loading of the prop and ultimately mark it as mergeable once it's loaded.
+
+```python
+from inertia import defer, inertia
+
+@inertia('ExampleComponent')
+def example(request):
+  return {
+    'name': lambda: 'Brandon', 
+    'data': defer(lambda: Paginator(objects, 3), merge=True), 
+  }
+```
+
 ### Json Encoding
 
 Inertia Django ships with a custom JsonEncoder at `inertia.utils.InertiaJsonEncoder` that extends Django's

inertia/__init__.py

@@ -1,3 +1,3 @@
 from .http import inertia, render, location
-from .utils import lazy, optional, defer
+from .utils import lazy, optional, defer, merge
 from .share import share

inertia/http.py

@@ -5,7 +5,7 @@
 from json import dumps as json_encode
 from functools import wraps
 import requests
-from .utils import DeferredProp, LazyProp
+from .prop_classes import IgnoreOnFirstLoadProp, DeferredProp, MergeableProp
 
 INERTIA_REQUEST_ENCRYPT_HISTORY = "_inertia_encrypt_history"
 INERTIA_SESSION_CLEAR_HISTORY = "_inertia_clear_history"
@@ -37,7 +37,7 @@ def build_props():
         if key not in partial_keys():
           del _props[key]
       else:
-        if isinstance(_props[key], LazyProp) or isinstance(_props[key], DeferredProp):
+        if isinstance(_props[key], IgnoreOnFirstLoadProp):
           del _props[key]
 
     return deep_transform_callables(_props)
@@ -52,7 +52,20 @@ def build_deferred_props():
         _deferred_props.setdefault(prop.group, []).append(key)
 
     return _deferred_props
-
+
+  def build_merge_props():
+    reset_keys = request.headers.get('X-Inertia-Reset', '').split(',')
+
+    return [
+      key 
+      for key, prop in props.items()
+      if (
+        isinstance(prop, MergeableProp)
+        and prop.should_merge()
+        and key not in reset_keys
+      )
+    ]
+
   def render_ssr():
     data = json_encode(page_data(), cls=settings.INERTIA_JSON_ENCODER)
     response = requests.post(
@@ -88,6 +101,10 @@ def page_data():
     if _deferred_props:
       _page['deferredProps'] = _deferred_props
 
+    _merge_props = build_merge_props()
+    if _merge_props:
+      _page['mergeProps'] = _merge_props
+
     return _page
 
   if 'X-Inertia' in request.headers:

inertia/prop_classes.py

@@ -0,0 +1,33 @@
+from abc import ABC, abstractmethod
+import warnings
+
+class CallableProp(ABC):
+  def __init__(self, prop):
+    self.prop = prop
+
+  def __call__(self):
+    return self.prop() if callable(self.prop) else self.prop
+
+class MergeableProp(ABC):
+  @abstractmethod
+  def should_merge(self):
+    pass
+
+class IgnoreOnFirstLoadProp(ABC):
+  pass
+
+class OptionalProp(CallableProp, IgnoreOnFirstLoadProp):
+  pass
+
+class DeferredProp(CallableProp, MergeableProp, IgnoreOnFirstLoadProp):
+  def __init__(self, prop, group, merge=False):
+    super().__init__(prop)
+    self.group = group
+    self.merge = merge
+
+  def should_merge(self):
+    return self.merge
+
+class MergeProp(CallableProp, MergeableProp):
+  def should_merge(self):
+    return True

inertia/test.py

@@ -29,6 +29,12 @@ def page(self):
 
   def props(self):
     return self.page()['props']
+
+  def merge_props(self):
+    return self.page()['mergeProps']
+
+  def deferred_props(self):
+    return self.page()['deferredProps']
 
   def template_data(self):
     context = self.mock_render.call_args.args[2]
@@ -53,7 +59,7 @@ def assertHasExactTemplateData(self, template_data):
   def assertComponentUsed(self, component_name):
     self.assertEqual(component_name, self.component())
 
-def inertia_page(url, component='TestComponent', props={}, template_data={}, deferred_props=None):
+def inertia_page(url, component='TestComponent', props={}, template_data={}, deferred_props=None, merge_props=None):
   _page = {
     'component': component,
     'props': props,
@@ -65,6 +71,9 @@ def inertia_page(url, component='TestComponent', props={}, template_data={}, def
 
   if deferred_props:
     _page['deferredProps'] = deferred_props
+
+  if merge_props:
+    _page['mergeProps'] = merge_props
 
   return _page
 

inertia/tests/test_rendering.py

@@ -162,3 +162,36 @@ def test_only_deferred_props_in_group_are_included_when_requested(self):
       self.inertia.get('/defer-group/', HTTP_X_INERTIA_PARTIAL_DATA='grit', HTTP_X_INERTIA_PARTIAL_COMPONENT='TestComponent'),
       inertia_page('defer-group', props={'grit': 'intense'})
     )
+
+class MergePropsTestCase(InertiaTestCase):
+  def test_merge_props_are_included_on_initial_load(self):
+    self.assertJSONResponse(
+      self.inertia.get('/merge/'),
+      inertia_page('merge', props={
+        'name': 'Brandon',
+        'sport': 'Hockey',
+      }, merge_props=['sport', 'team'], deferred_props={'default': ['team']})
+    )
+
+
+  def test_deferred_merge_props_are_included_on_subsequent_load(self):
+    self.assertJSONResponse(
+      self.inertia.get('/merge/', HTTP_X_INERTIA_PARTIAL_DATA='team', HTTP_X_INERTIA_PARTIAL_COMPONENT='TestComponent'),
+      inertia_page('merge', props={
+        'team': 'Penguins',
+      }, merge_props=['sport', 'team'])
+    )
+
+  def test_merge_props_are_not_included_when_reset(self):
+    self.assertJSONResponse(
+      self.inertia.get(
+        '/merge/',
+        HTTP_X_INERTIA_PARTIAL_DATA='sport,team',
+        HTTP_X_INERTIA_PARTIAL_COMPONENT='TestComponent',
+        HTTP_X_INERTIA_RESET='sport,team'
+      ),
+      inertia_page('merge', props={
+        'sport': 'Hockey',
+        'team': 'Penguins',
+      })
+    )

inertia/tests/testapp/urls.py

@@ -10,7 +10,8 @@
   path('lazy/', views.lazy_test),
   path('optional/', views.optional_test),
   path('defer/', views.defer_test),
-  path('defer-group/', views.defer_group_test), 
+  path('defer-group/', views.defer_group_test),
+  path('merge/', views.merge_test),
   path('complex-props/', views.complex_props_test),
   path('share/', views.share_test),
   path('inertia-redirect/', views.inertia_redirect_test),

inertia/tests/testapp/views.py

@@ -1,7 +1,7 @@
 from django.http.response import HttpResponse
 from django.shortcuts import redirect
 from django.utils.decorators import decorator_from_middleware
-from inertia import inertia, render, lazy, optional, defer, share, location
+from inertia import inertia, render, lazy, merge, optional, defer, share, location
 from inertia.http import INERTIA_SESSION_CLEAR_HISTORY, clear_history, encrypt_history
 
 class ShareMiddleware:
@@ -77,6 +77,14 @@ def defer_group_test(request):
     'grit': defer(lambda: 'intense')
   }
 
+@inertia('TestComponent')
+def merge_test(request):
+  return {
+    'name': 'Brandon',
+    'sport': merge(lambda: 'Hockey'),
+    'team': defer(lambda: 'Penguins', merge=True),
+  }
+
 @inertia('TestComponent')
 def complex_props_test(request):
   return {

inertia/utils.py

@@ -2,6 +2,7 @@
 from django.db import models
 from django.db.models.query import QuerySet
 from django.forms.models import model_to_dict as base_model_to_dict
+from .prop_classes import OptionalProp, DeferredProp, MergeProp
 import warnings
 
 def model_to_dict(model):
@@ -17,35 +18,19 @@ def default(self, value):
 
     return super().default(value)
 
-class LazyProp:
-  def __init__(self, prop):
-    warnings.warn(
-      "lazy and LazyProp are deprecated and will be removed in a future version. Please use optional instead.",
-      DeprecationWarning,
-      stacklevel=2
-    )
-    self.prop = prop
-
-  def __call__(self):
-    return self.prop() if callable(self.prop) else self.prop
-
-class OptionalProp(LazyProp):
-  def __init__(self, prop):
-    self.prop = prop
-
-class DeferredProp:
-  def __init__(self, prop, group):
-    self.prop = prop
-    self.group = group
-
-  def __call__(self):
-    return self.prop() if callable(self.prop) else self.prop
-
 def lazy(prop):
-  return LazyProp(prop)
+  warnings.warn(
+    "lazy is deprecated and will be removed in a future version. Please use optional instead.",
+    DeprecationWarning,
+    stacklevel=2
+  )
+  return optional(prop)
 
 def optional(prop):
   return OptionalProp(prop)
 
-def defer(prop, group="default"):
-  return DeferredProp(prop, group)
+def defer(prop, group="default", merge=False):
+  return DeferredProp(prop, group=group, merge=merge)
+
+def merge(prop):
+  return MergeProp(prop)