Extracting Admin ManyToManyField to CSV file

Question

I'm currently trying to learn django. I'm working on a personal project. I'm trying to create an action in the admin panel for extracting data from my model to a CSV File. For example, I have the following Model:

class OrderItem(models.Model):
    order = models.ForeignKey(Order, related_name='items', on_delete=models.CASCADE)
    type_product = models.ForeignKey(Sous_Categories_Article, verbose_name="Catégorie Article", on_delete=models.PROTECT)
    product = models.ManyToManyField(Variations_Articles, max_length=1000, verbose_name='Article')
    price = models.DecimalField(max_digits=10, decimal_places=2)
    quantity = models.PositiveIntegerField(default=1)

I use the following code at that time:

def export_to_csv(modeladmin, request, queryset):
    opts = modeladmin.model._meta
    response = HttpResponse(content_type='text/csv')
    response['Content-Disposition'] = 'attachment; filename=%s.csv' % str(opts).replace('.', '_')

    writer = csv.writer(response, delimiter=";")
    fields = []
    fields = [field for field in opts.get_fields()]

    writer.writerow([field.name.title() for field in fields])


    for obj in queryset:
        data_row = []
        for field in fields:        
            if field.many_to_many == True or field.one_to_many == True:
                try:
                    value = list(getattr(obj,field.name).all().values_list('id', flat=True))
                except:
                value = str(obj).replace(";", "")
            else:
                value = str(getattr(obj, field.name)).replace(";", "")
            if isinstance(value, datetime.datetime):
                value = value.strftime('%d/%m/%Y')
            data_row.append(value)
        writer.writerow(data_row)
    return response

export_to_csv.short_description = 'Export to CSV'

I have two questions. I like to extract other models that have ManyToManyField or One to Many Field. How can i proceed? The following code only applies to a specific Model:

values = obj.product.all().values_list('id', flat=True)

How can I use a "variable" in my query instead of duplicating the code for each model?

My second question is about creating a new line each time there are several records in the many to many field. For example, as mentioned above, an order could have several products. I'd like to create a new line for each product in the order (duplicating data):

Order 1 Type_Product Quantity Price Product 1
Order 1 Type_Product Quantity Price Product 2

At that time, I was able to create one line:

Order 1 Type_Product Quantity Price Product 1 Product 2

Thank you for your help,

Singertwist

Question 2: solution (not the best one but working)

def export_to_csv_sales(modeladmin, request, queryset):
    opts = modeladmin.model._meta
    response = HttpResponse(content_type='text/csv')
    response['Content-Disposition'] = 'attachment; filename=%s.csv' % str(opts).replace('.', '_')
    writer = csv.writer(response, delimiter=";")
    # fields = [field for field in opts.get_fields() if not field.many_to_many and not field.one_to_many]
    fields = []
    fields = [field for field in opts.get_fields()]

# Write a first row with header information
# writer.writerow([field.verbose_name.title() for field in fields]) # Title nécessaire car sinon ID est le premier champ et provoque un avertissement lors de l'ouverture sous Excel( fichier de type Sylk).
writer.writerow([field.name.title() for field in fields])


# Write data rows
for obj in queryset:
    data_row = []
    for field in fields:        
        if field.many_to_many == True or field.one_to_many == True:
            try:
                values = list(getattr(obj, field.name).all().values_list('id', flat=True)) # On récupérère sous forme de liste les id relatifs aux articles.
            except:
                value = str(obj).replace(";", "") # Replace permet de supprimer les point virgule des chaines de caractères afin de ne pas interférer avec le séparateur du CSV.
        else:
            value = str(getattr(obj, field.name)).replace(";", "") # Replace permet de supprimer les point virgule des chaines de caractères afin de ne pas interférer avec le séparateur du CSV.
        if isinstance(value, datetime.datetime):
            value = value.strftime('%d/%m/%Y')
        data_row.append(value) # On aggrège toutes les données d'une ligne dans la liste data_row.

    # Si values est différent de None, cela veut dire que l'on a une liste présente dans la commande. Donc une composition. On va créé pour une ligne pour chaque item de la composition. 
    if values != None:
        for data in values: # On parcours la liste contenant les différents ingrédients de la commande.
            data_row[-1] = data # On remplace la liste par les données de la liste. Pour sélectionner la dernière colonne contenant les produits, on utilise l'index [-1], le -1 signifie que l'on sélection la première colonne en partant de la fin.
            writer.writerow(data_row) # On écrit une ligne avec l'ID qui a été inséré
    else:
        writer.writerow(data_row) # S'il n'y a pas de composition on écrit la ligne normalement.
return response

export_to_csv_sales.short_description = 'Exporter au format CSV'

Answer 1

For your first question: have you tried this?

values = getattr(obj, field_name).all().values_list('id', flat=True)

You should get field_name within your code. I think you have it there.