More data for custom label printing mixin

[luwol03]

Hey,

what would be the best way to get more data about a part/location/stock item via a custom LabelPrintingMixin? My first thought was to use some external library to decode the QR to text and the use the inventree API to fetch more info about the part which can then be used to be also printed on the label. But this feels like a bad workaround. Can you please let me know if there is no other option and how do I make sure, that the QR code library which is needed for decoding will be installed on plugin install?

[matmair]

@luwol03 I am not sure why you would need extra information in a plugin exposing LabelPrintingMixin APIs. This is generally meant to only take the pdf / picture and send it to some kind of printer. Kind of like a printer driver in an OS.
Maybe it will help my understanding if you give a small example what you want to achive. If you want to add information to a label my suggestion would be to change the label itself, you have access to nearly everything in the templating engine.
Plugins are generally meant to be distributed as a python packages (either via PyPi, a VCS or a private index like githubs) , you just need to add the required libraries as a requirement in the setup (see the deployment advice in the docs / the packaging page)

[SchrodingersGat]

@luwol03 to retrieve the full error message you will need to navigate to the "admin" page and share the error report - https://inventree.readthedocs.io/en/latest/settings/logs/

[luwol03]

@SchrodingersGat, sorry that I forgot this. This is the error I got.

Error

Traceback (most recent call last):

File "/home/inventree/InvenTree/plugin/base/label/label.py", line 47, in print_label
plugin.print_label(

File "/home/inventree/InvenTree/plugins/print_label.py", line 24, in print_label
print("-> LABEL - INSTANCE DATA 123", kwargs["label_instance"].get_context_data())

TypeError: get_context_data() missing 1 required positional argument: 'request'

Then I noticed, that I need to hand over None manually for the request argument, which is ok I think, because here its also set to None if not defined. After doing this, this is the new error:

Error

Traceback (most recent call last):

File "/home/inventree/InvenTree/plugin/base/label/label.py", line 47, in print_label
plugin.print_label(

File "/home/inventree/InvenTree/plugins/print_label.py", line 24, in print_label
print("-> LABEL - INSTANCE DATA 123", kwargs["label_instance"].get_context_data(None))

File "/home/inventree/InvenTree/label/models.py", line 314, in get_context_data
'category': part.category,

AttributeError: 'NoneType' object has no attribute 'category'

but then I get this error. It seems like there is no label instance handed over with the self.object_to_print attribute. So I tried to analyze the call stack:

Call stack

From what I got, the call stak is as follows:

1. InvenTree/InvenTree/label/api.py

   Line 500 in cf70e42

   def get(self, request, *args, **kwargs):

   gets called by the webUI via a GET request
2. because this class extends the PartLabelMixin, the following get_parts() method get called

   InvenTree/InvenTree/label/api.py

   Line 418 in cf70e42

   def get_parts(self):

   which fetches all parts from the db provided in the queryparams.
3. because the class extends the LabelPrintMixin with

   InvenTree/InvenTree/label/api.py

   Line 504 in cf70e42

   return self.print(request, parts)

   this method gets called:

   InvenTree/InvenTree/label/api.py

   Line 80 in cf70e42

   def print(self, request, items_to_print):

4. then all outputs are constructed with its own correct label instance

   InvenTree/InvenTree/label/api.py

   Lines 99 to 111 in cf70e42

   	# Merge one or more PDF files into a single download
   	for item in items_to_print:
   	label = self.get_object()
   	label.object_to_print = item
   	label_name = label.generate_filename(request)
   	label_names.append(label_name)
   	if debug_mode:
   	outputs.append(label.render_as_string(request))
   	else:
   	outputs.append(label.render(request))

5. then one new dummy label_instance is constructed (it has no object_to_print

   InvenTree/InvenTree/label/api.py

   Line 127 in cf70e42

   label_instance = self.get_object()

6. and then you iterate over all output items and always provide the same label_instance with the different rendered pdf files to the offload_task method

   InvenTree/InvenTree/label/api.py

   Lines 129 to 143 in cf70e42

   	for idx, output in enumerate(outputs):
   	"""For each output, we generate a temporary image file, which will then get sent to the printer."""
   	# Generate PDF data for the label
   	pdf = output.get_document().write_pdf()
   	# Offload a background task to print the provided label
   	offload_task(
   	plugin_label.print_label,
   	plugin.plugin_slug(),
   	pdf,
   	filename=label_names[idx],
   	label_instance=label_instance,
   	user=request.user,
   	)

7. the offloaded task then calls

   InvenTree/InvenTree/plugin/base/label/label.py

   Line 18 in d32054b

   def print_label(plugin_slug: str, pdf_data, filename=None, label_instance=None, user=None):

8. which then calls my plugin

   InvenTree/InvenTree/plugin/base/label/label.py

   Lines 47 to 55 in d32054b

   	plugin.print_label(
   	pdf_data=pdf_data,
   	png_file=png_file,
   	filename=filename,
   	label_instance=label_instance,
   	width=label_instance.width,
   	height=label_instance.height,
   	user=user
   	)

Patch

So I suggest the following patch for step 5. If you like that, should I create an PR for that?

diff --git a/InvenTree/label/api.py b/InvenTree/label/api.py
index 7b533c882..68c420517 100644
--- a/InvenTree/label/api.py
+++ b/InvenTree/label/api.py
@@ -95,6 +95,7 @@ class LabelPrintMixin:
         label_name = "label.pdf"
 
         label_names = []
+        label_instances = []
 
         # Merge one or more PDF files into a single download
         for item in items_to_print:
@@ -104,6 +105,7 @@ class LabelPrintMixin:
             label_name = label.generate_filename(request)
 
             label_names.append(label_name)
+            label_instances.append(label)
 
             if debug_mode:
                 outputs.append(label.render_as_string(request))
@@ -123,9 +125,6 @@ class LabelPrintMixin:
             - Return a JSON response indicating that the printing has been offloaded
             """
 
-            # Label instance
-            label_instance = self.get_object()
-
             for idx, output in enumerate(outputs):
                 """For each output, we generate a temporary image file, which will then get sent to the printer."""
 
@@ -138,7 +137,7 @@ class LabelPrintMixin:
                     plugin.plugin_slug(),
                     pdf,
                     filename=label_names[idx],
-                    label_instance=label_instance,
+                    label_instance=label_instances[idx],
                     user=request.user,
                 )

[SchrodingersGat]

@luwol03 seems like a reasonable patch, allowing you to fully recreate the label context in a plugin, if required.

[matmair]

Patch looks good

[luwol03]

Patched in #3349 for reference.