django-tastypie and many to many “through” relationships

Question

In Django and Tastypie I'm attempting to figure out how to properly deal with Many to Many "through" relationships, like those found here: https://docs.djangoproject.com/en/dev/topics/db/models/#extra-fields-on-many-to-many-relationships

Here are my sample models:

class Ingredient(models.Model):
    name = models.CharField(max_length=100)
    description = models.TextField()

class RecipeIngredients(models.Model):
    recipe = models.ForeignKey('Recipe')
    ingredient = models.ForeignKey('Ingredient')
    weight = models.IntegerField(null = True, blank = True)

class Recipe(models.Model):
    title = models.CharField(max_length=100)
    ingredients = models.ManyToManyField(Ingredient, related_name='ingredients', through='RecipeIngredients', null = True, blank = True)

Now my api.py file:

class IngredientResource(ModelResource):
    ingredients = fields.ToOneField('RecipeResource', 'ingredients', full=True)

    class Meta:
        queryset = Ingredient.objects.all()
        resource_name = "ingredients"


class RecipeIngredientResource(ModelResource):
    ingredient = fields.ToOneField(IngredientResource, 'ingredients', full=True)
    recipe = fields.ToOneField('RecipeResource', 'recipe', full=True)

    class Meta:
        queryset= RecipeIngredients.objects.all()


class RecipeResource(ModelResource):
    ingredients = fields.ToManyField(RecipeIngredientResource, 'ingredients', full=True)

class Meta:
    queryset = Recipe.objects.all()
    resource_name = 'recipe'

I'm trying to base my code on this example: http://pastebin.com/L7U5rKn9

Unfortunately, with this code I get this error:

"error_message": "'Ingredient' object has no attribute 'recipe'"

Does anyone know what's happening here? Or how I can include the name of the ingredient in the RecipeIngredientResource? Thanks!

EDIT:

I may have found the error myself. ToManyField should be directed toward Ingredient and not RecipeIngredient. I'll see if this does the job.

EDIT:

New error.. any ideas? The object '' has an empty attribute 'title' and doesn't allow a default or null value.

Answer 1

You mentioned:

I may have found the error myself. ToManyField should be directed toward Ingredient and not RecipeIngredient. I'll see if this does the job.

There's a better approach though [Tastypie M2M](http://blog.eugene-yeo.in/django-tastypie-manytomany-through.html) (old blog is offline: https://github.com/9gix/eugene-yeo.in/blob/master/content/web/django-tastiepie-m2m.rst)

In short summary, Instead of ToManyField to Ingredients, I use ToManyField toward the ThroughModel. And customize the attribute kwargs to be a callback function that return the ThroughModel Queryset.

Update (2014 Apr)

This answer is made long ago. Not sure if it is still useful.

Answer 2

I had the same issue as you. To solve it, I simply just removed the ToMany field (like in RecipeResource) from the API. This worked for us because the model still had the the manytomany field (just not the API), and you could still query the relation by querying the intermediate model instead.