django admin - add custom form fields that are not part of the model

Question

I have a model registered in the admin site  One of its fields is a long string expression  I d like to add custom form fields to the add update page of this model in the admin that based on these fields values I will build the long string expression and save it in the relevant model field   How can I do that   UPDATE  Basically what I m doing is building a mathematical or string expression from symbols  the user chooses symbols  these are the custom fields that are not part of the model  and when he clicks save then I create a string expression representation from the list of symbols and store it in the DB  I don t want the symbols are part of the model and DB  only the final expression

User · Answer

Either in your admin py or in a separate forms py you can add a ModelForm class and then declare your extra fields inside that as you normally would  I ve also given an example of how you might use these values in form save     from django import forms from yourapp models import YourModel   class YourModelForm forms ModelForm        extra field   forms CharField        def save self  commit True           extra field   self cleaned data get  extra field   None               do something with extra field here            return super YourModelForm  self  save commit commit       class Meta          model   YourModel   To have the extra fields appearing in the admin just    edit your admin py and set the form property to refer to the form you created above include your new fields in your fields or fieldsets declaration   Like this   class YourModelAdmin admin ModelAdmin        form   YourModelForm      fieldsets              None                 fields     name    description    extra field                         UPDATE  In django 1 8 you need to add fields      all    to the metaclass of YourModelForm

User · Answer

you can always create new admin template   and do what you need in your admin view  override the admin add url to your admin view     url r  admin mymodel mymodel add       admin views add my special model

User · Answer

If you absolutely only want to store the combined field on the model and not the two seperate fields  you could do something like this    Create a custom form using the form attribute on your ModelAdmin  https   docs djangoproject com en dev ref contrib admin  django contrib admin ModelAdmin form  Parse the custom fields in the save formset method on your ModelAdmin  https   docs djangoproject com en dev ref contrib admin  django contrib admin ModelAdmin save model    I never done something like this so I m not completely sure how it will work out

User · Answer

Django 2 1 1 The primary answer got me halfway to answering my question  It did not help me save the result to a field in my actual model   In my case I wanted a textfield that a user could enter data into  then when a save occurred the data would be processed and the result put into a field in the model and saved   While the original answer showed how to get the value from the extra field  it did not show how to save it back to the model at least in Django 2 1 1  This takes the value from an unbound custom field  processes  and saves it into my real description field   class WidgetForm forms ModelForm       extra field   forms CharField required False       def processData self  input             example of error handling         if False              raise forms ValidationError  Processing failed             return input     has been processed       def save self  commit True           extra field   self cleaned data get  extra field   None             self description    my result  note that this does not work            Get the form instance so I can write to its fields         instance   super WidgetForm  self  save commit commit             this writes the processed data to the description field         instance description   self processData extra field           if commit              instance save            return instance      class Meta          model   Widget         fields      all

User · Answer

It it possible to do in the admin  but there is not a very straightforward way to it  Also  I would like to advice to keep most business logic in your models  so you won t be dependent on the Django Admin   Maybe it would be easier  and maybe even better  if you have the two seperate fields on your model  Then add a method on your model that combines them   For example   class MyModel models model        field1   models CharField max length 10      field2   models CharField max length 10       def combined fields self           return         format self field1  self field2    Then in the admin you can add the combined fields   as a readonly field   class MyModelAdmin models ModelAdmin        list display     field1    field2    combined fields       readonly fields     combined fields         def combined fields self  obj           return obj combined fields     If you want to store the combined fields in the database you could also save it when you save the model   def save self   args    kwargs       self field3   self combined fields       super MyModel  self  save  args    kwargs

[django] django admin - add custom form fields that are not part of the model

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