How to handle nested backward lookups in a template for a generic detail view?

[Thomas Hughes]

I have a generic detail view serving content for 'project' to an HTML template with the following code: 

{% for detail in project.projectdetail_set.all %}
    {% for image in detail.projectdetailimage_set.all %}
        do something with image
    {% endfor %}
{% endfor %}

and my models look like:

class Project(models.Model):
    name = models.CharField(max_length=1000)
    start_date = models.DateField()
    abstract = models.TextField()
    abstract_image = models.ImageField(storage=PROJECT_STORAGE)

    def __str__(self):
        return self.name

class ProjectDetail(models.Model):
    project = models.ForeignKey(Project, on_delete=models.CASCADE)
    name = models.CharField(max_length=1000)
    text = models.TextField()

    def __str__(self):
        return self.name

class ProjectDetailImage(models.Model):
    detail = models.ForeignKey(ProjectDetail, on_delete=models.CASCADE)
    image = models.ImageField(storage=PROJECT_STORAGE)

It looks like generic detail view only arranges for backward lookup on the 'project' via .projectdetail_set.all but not on the 'detail' as the HTML for .projectdetailimage_set.all just never shows up in the HTML source. I am wondering then what is the proper way to handle nested ForeignKeys like this, basically like a Book > Section > Chapter structure where a Book has several Sections and a Section has several Chapters and Chapters are only associated with Sections and Sections are only associated with Books.

[Thomas Hughes]

Just FYI - the issue was with using 'image.url' rather than 'image.image.url' in code labeled with 'do something with image' in the HTML template above.

["Александр Христюхин (roboslone)"]

Hi,

First of all, you can use `related_name` in your model fields to get pretty backref names (so you don't have to use image_set everywhere).

Second, you're missing dots in your template (`for detail in project.projectdetail_set.all`).

And finally, your model is called ProjectDetailImage and it has a field, that is named `image`. So you won't be able to get rid of `image.image.url`. However, you can move your image to ProjectDetail model (add field `image = models.ImageField(...)`) and use it like so:

{% for detail in project.projectdetail_set.all %}

    <img src="{{ detail.image.url }}"/>

{% endfor %}

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["Александр Христюхин (roboslone)"]

Whoops, looks like all dots are in place, my mistake. First and last points are still valid, though.

[Thomas Hughes]

Thank you for your reply.

I understand your third point.  In this application though I have a many images to a single detail structure.

For your first point "use `related_name` in your model fields to get pretty backref names (so you don't have to use image_set everywhere)", how do I do that and maintain the ability to reference the data via the two-fold nested loop I need in my HTML template?

Thanks,

Tom

["Александр Христюхин (roboslone)"]

You still can reference the data:

class Foo(models.Model):

    pass

class Bar(models.Model):

    foo = models.ForeignKey(Foo, related_name='bars')

f = Foo()

b1 = Bar(foo=f)

b2 = Bar(foo=f)

f.bars.all()  # <QuerySet [b1, b2]>

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