Tutorial¶

Note

This tutorial is intended for a reader that is well versed in the Django basics of the ORM, urls routing, function based views, and templates.

It is also expected that you have already installed iommi in your project. Read section 1 of Getting started.

In this tutorial you will build a discography app. By the end you will have:

an index page with album artwork
an artist page, and a page listing artists
an album page, and a page listing albums
a tracks page
the iommi admin, enabled for all of these

Every step shows the code and the page it produces. Type the code in as you go; each step builds on the one before it.

Set up¶

Put these models in your app’s models.py:

class Genre(Model):
    name = CharField(max_length=255, db_index=True)

class Artist(Model):
    name = CharField(max_length=255, db_index=True)

class Album(Model):
    name = CharField(max_length=255, db_index=True)
    artist = ForeignKey(Artist, on_delete=CASCADE, related_name='albums')
    year = IntegerField(default=1980)
    genres = ManyToManyField(Genre, related_name='albums')
    published_date = DateField(null=True, blank=True)

class Track(Model):
    name = CharField(max_length=255, db_index=True)
    index = IntegerField()
    album = ForeignKey(Album, on_delete=CASCADE, related_name='tracks')
    duration = CharField(max_length=255, db_index=False, null=True, blank=True)

Create the tables:

python manage.py makemigrations
python manage.py migrate

Now load the same example data used in this tutorial, so your pages look like the screenshots. Download big_discography.py into your project and run it:

python manage.py shell < big_discography.py

You’re ready to build the first page.

# Regenerates the example data script that the `Set up` section of this page
# links to. Nothing is rendered into the docs from here.

Tables¶

Creating a table view of a model in iommi is simple:

urlpatterns = [
    path('', Table(auto__model=Album).as_view()),
]

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You get sorting and pagination by default, and we’re using the default bootstrap 5 style. iommi ships with more styles that you can switch to, or you can implement your own custom style.

At this point you might think “Hold on! Where is the template?”. There isn’t one. We don’t need a template. iommi works at a higher level of abstraction. Don’t worry, you can drop down to templates if you need to. There are examples of this in the table cookbook, and much more. One of the most important concepts is to include or exclude columns using includes: auto__include=['name', 'artist'], or using excludes: auto__exclude=['artist', 'year'].

Pages¶

So far we’ve just created a single table, but often you want something a little more complex, especially for your index page. iommi has a concept of a Page that is used to build up a bigger page from smaller building blocks. Let’s build out our simple web app to have separate pages for albums, artists and tracks:

urlpatterns = [
    path('albums/', Table(auto__model=Album).as_view()),
    path('artists/', Table(auto__model=Artist).as_view()),
    path('tracks/', Table(auto__model=Track).as_view()),
]

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and an index page with three tables, a header and some text:

class IndexPage(Page):
    title = html.h1('Supernaut')
    welcome_text = 'This is a discography of the best acts in music!'

    artists = Table(auto__model=Artist, page_size=5)
    albums = Table(auto__model=Album, page_size=5)
    tracks = Table(auto__model=Track, page_size=5)

urlpatterns = [
    path('', IndexPage().as_view()),
]

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html is a little fragment builder to make it easier and faster to build small html parts. html.div('foo') is just a more convenient way to write Fragment(tag='div', children__text='foo'). Fragments are used internally throughout iommi, because they allow you to define a small bit of html that can be customized later. Let’s look at an example:

>>> class MyPage(Page):
...    title = html.h1('Supernaut')

>>> MyPage().bind().__html__()
'<h1>Supernaut</h1>'

>>> MyPage(parts__title__attrs__class__foo=True).bind().__html__()
'<h1 class="foo">Supernaut</h1>'

This is used throughout iommi to provide good defaults that can be customized easily when needed.

A Page can contain any Part (like Fragment, Table, Form, Menu, etc), plain strings or Django Template objects even. Escaping is handled like you’d expect from Django where strings are escaped, and you can use format_html/mark_safe to send your raw html straight through.

Path decoding¶

We’ll also introduce a page for an individual artist. We will use iommi’s Path decoding here.

First we register the path component we want to decode (in your AppConfig ready):

register_path_decoding(
    artist_name=Artist.name,
)

Then we define our page. Notice the lambdas we use to dynamically get the parameters to retrieve the correct data.

class ArtistPage(Page):
    title = html.h1(lambda artist, **_: artist.name)

    albums = Table(
        auto__model=Album,
        rows=lambda artist, **_: Album.objects.filter(artist=artist),
    )
    tracks = Table(
        auto__model=Track,
        rows=lambda artist, **_: Track.objects.filter(album__artist=artist),
    )

urlpatterns = [
    path('artist/<artist_name>/', ArtistPage().as_view()),
]

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Path decoders in iommi can be more convenient compared to Django path decoders, as instead of writing <artist:artist> everywhere, you can instead write <artist_name> or <artist_pk>. They are also easier to set up and give you hook points for access control if needed.

Customize the table¶

Change how a value is displayed¶

Add get_absolute_url to your Album and Artist models, then let’s make the album name link to the album page. cell__url turns a cell into a link:

albums = Table(
    auto__model=Album,
    columns__name__cell__url=lambda row, **_: row.get_absolute_url(),
)

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Notice that the artist column became a link too, without you asking for it: for a ForeignKey column iommi does this by default when the target model has get_absolute_url.

columns__name__cell__url reads as columns.name.cell.url. iommi uses __ to step down into nested configuration, because . isn’t valid in a keyword argument. You’ll see this everywhere from here on; Double underscore short form explains it properly.

When you need to build the displayed string yourself rather than just link it, use cell__format:

albums = Table(
    auto__model=Album,
    columns__artist__cell__format=lambda value, **_:
        format_html('<a href="/artist/{}/">{}</a>', value, value)
)

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There is a ladder of hooks here, and you reach for the lowest one that does the job: attr picks which attribute is read, value computes the value, format turns the value into a string, and template replaces the cell’s rendering outright, td tag included. Rows have a template too.

Add filtering¶

Tables also have built in filtering. To enable a filter make sure include is True for the filter of a column.

albums = Table(
    auto__model=Album,
    columns__name__filter__include=True,
    columns__year__filter__include=True,
    columns__year__filter__field__include=False,
    columns__artist__filter__include=True,
)

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columns__year__filter__field__include=False means we turn off the Field in the form that is created, but we can still search for the year in the advanced search language.

To handle selecting from a choice field that is backed by a QuerySet that can contain thousands or millions of rows, iommi by default uses a select2 filter control with an automatic ajax endpoint. The automatic endpoint is handled by iommi on the same url as the view. An advantage to this approach is that we only need to be sure our view has the correct permission checks and then we also know the select box (or ajax endpoint) has the same checks. This makes it easy to reason about the security of the product.

The advanced filter means users can write queries like year>1960 and title:war to find albums published after 1960 and that contain the word “war”.

Add buttons, and edit/delete links for staff¶

An Action in iommi is a link or a button. Let’s add a create button, plus edit and delete columns, and show all three only to staff. Column.edit and Column.delete are prebuilt shortcuts for the link columns:

albums = Table(
    auto__model=Album,
    actions__create_album=Action(
        attrs__href='/albums/create/',
        include=lambda request, **_: request.user.is_staff,
    ),
    columns__edit=Column.edit(
        after=0,
        include=lambda request, **_: request.user.is_staff,
    ),
    columns__delete=Column.delete(
        include=lambda request, **_: request.user.is_staff,
    ),
)

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For non-staff the “Create album” button isn’t shown, neither are the edit and delete columns:

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Show album art in a column¶

Now that we have a basic app, let’s make the index page look better. A plain table of text doesn’t look very cool, so we’ll add the album covers.

Add a column that has no model field behind it (attr=None) and give it a template that renders an image:

albums = Table(
    auto__model=Album,
    columns__album_art=Column(
        attr=None,
        cell__template=Template('''
            <td>
                <img
                    height="30"
                    src="../../album_art/{{ row.artist }}/{{ row.name }}.jpg">
            </td>
        '''),
    ),
)

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That’s a start, but we want something more showy, so let’s get rid of the html table entirely.

Turn the rows into cards¶

row__template replaces the rendering of a whole row, tr tag included. Render the table as a div instead of a table, turn off the header, and make each row a card:

albums = Table(
    auto__model=Album,
    tag='div',
    header__template=None,
    row__template=Template("""
        <div class="card" style="width: 15rem; display: inline-block;" {{ cells.attrs }}>
            <img class="card-img-top" src="../../album_art/{{ row.artist }}/{{ row.name|urlencode }}.jpg">
            <div class="card-body text-center">
                <h5>{{ cells.name }}</h5>
                <p class="card-text">
                    {{ cells.artist }}
                </p>
            </div>
        </div>
    """),
)

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You can specify the name of a template file here instead of writing the template inline like this. This way is nicer for small things and quick prototypes though.

Admin¶

With these high level abstractions we’ve seen so far (pages, tables, queries, forms, fragments) we can easily build more powerful components. Which is what we’ve done with the administration interface built into iommi. Installing it is as simple as:

class MyAdmin(Admin):
    class Meta:
        pass

urlpatterns = [
    path('iommi-admin/', include(MyAdmin.urls())),
]

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Customization is easy with IOMMI_DEBUG on (default on if DEBUG is on), here’s how to use the pick tool:

You can override an entire field rendering with template, the template of the label with label__template, the name of a field with display_name, add a CSS class to the label tag with label__attrs__class__foo=True, and much more. Customization is at all levels, and in all these cases you can supply a callable for even more flexibility.

Forms¶

iommi also comes with a library for forms. This can look very much like the forms library built into Django, but is different in some crucial ways. Let’s take a simple example of a ModelForm:

from django import forms

class AlbumForm(forms.ModelForm):
    class Meta:
        model = Album
        fields = ['name', 'artist']

{% extends "base.html" %}
{% block content %}

<form action="/your-name/" method="post">
    {% csrf_token %}
    {{ form }}
    <input type="submit" value="Submit">
</form>

{% endblock %}

In iommi the same can be written as:

class AlbumForm(Form):
    class Meta:
        auto__model = Album
        auto__include = ['name', 'artist']

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No template needed, and this is the view too with Form.edit or Form.create.

In iommi you always get a form encoding specified on the form, so they all work with file uploads. Missing form encoding on the form tag is a very common stumbling block for beginners. You also get a submit action by default which you can configure via actions__submit:

class AlbumForm(Form):
    class Meta:
        auto__model = Album
        auto__include = ['name', 'artist']
        actions__submit__display_name = 'Save'

Everything you put in class Meta is passed to the constructor, and only valid constructor arguments are accepted there – so a misspelled setting is an error, not silence. Equivalence covers what that buys you.

There are many more customization options available, you can find more in the form cookbook and the docs for Field.

Automatic views¶

iommi goes a step further than Django forms, by supplying full views that can be used from either a declarative form or an auto generated form. An example is to have a create view for an Artist:

urlpatterns = [
    path('create/', Form.create(auto__model=Artist).as_view()),
]

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There are four built in forms/views like this: create, edit, create_and_edit and delete. The delete view is a read only form with some styling for the submit button and a submit handler that deletes the object. We find this to be really nice as a confirmation page because you can see what you are about to delete.

Wrap up¶

I’m glad you read this far! This has been a very shallow introduction, but it has touched on all the major parts in some way, and there is a lot of material to cover. We hope you want to give iommi a try.