Custom pages and templates

Datasette provides a number of ways of customizing the way data is displayed.

CSS classes on the <body>

Every default template includes CSS classes in the body designed to support custom styling.

The index template (the top level page at /) gets this:

<body class="index">

The database template (/dbname) gets this:

<body class="db db-dbname">

The custom SQL template (/dbname?sql=...) gets this:

<body class="query db-dbname">

A canned query template (/dbname/queryname) gets this:

<body class="query db-dbname query-queryname">

The table template (/dbname/tablename) gets:

<body class="table db-dbname table-tablename">

The row template (/dbname/tablename/rowid) gets:

<body class="row db-dbname table-tablename">

The db-x and table-x classes use the database or table names themselves if they are valid CSS identifiers. If they aren't, we strip any invalid characters out and append a 6 character md5 digest of the original name, in order to ensure that multiple tables which resolve to the same stripped character version still have different CSS classes.

Some examples:

"simple" => "simple"
"MixedCase" => "MixedCase"
"-no-leading-hyphens" => "no-leading-hyphens-65bea6"
"_no-leading-underscores" => "no-leading-underscores-b921bc"
"no spaces" => "no-spaces-7088d7"
"-" => "336d5e"
"no $ characters" => "no--characters-59e024"

<td> and <th> elements also get custom CSS classes reflecting the database column they are representing, for example:

<table>
    <thead>
        <tr>
            <th class="col-id" scope="col">id</th>
            <th class="col-name" scope="col">name</th>
        </tr>
    </thead>
    <tbody>
        <tr>
            <td class="col-id"><a href="...">1</a></td>
            <td class="col-name">SMITH</td>
        </tr>
    </tbody>
</table>

Writing custom CSS

Custom templates need to take Datasette's default CSS into account. The pattern portfolio at /-/patterns (example here) is a useful reference for understanding the available CSS classes.

The core class is particularly useful - you can apply this directly to a <input> or <button> element to get Datasette's default form styles, or you can apply it to a containing element (such as <form>) to apply those styles to all of the form elements within it.

Serving static files

Datasette can serve static files for you, using the --static option. Consider the following directory structure:

metadata.json
static-files/styles.css
static-files/app.js

You can start Datasette using --static assets:static-files/ to serve those files from the /assets/ mount point:

datasette --config datasette.yaml --static assets:static-files/ --memory

The following URLs will now serve the content from those CSS and JS files:

http://localhost:8001/assets/styles.css
http://localhost:8001/assets/app.js

You can reference those files from datasette.yaml like this, see custom CSS and JavaScript for more details:

extra_css_urls:
- /assets/styles.css
extra_js_urls:
- /assets/app.js
{
  "extra_css_urls": [
    "/assets/styles.css"
  ],
  "extra_js_urls": [
    "/assets/app.js"
  ]
}

Publishing static assets

The datasette publish command can be used to publish your static assets, using the same syntax as above:

datasette publish cloudrun mydb.db --static assets:static-files/

This will upload the contents of the static-files/ directory as part of the deployment, and configure Datasette to correctly serve the assets from /assets/.

Custom templates

By default, Datasette uses default templates that ship with the package.

You can over-ride these templates by specifying a custom --template-dir like this:

datasette mydb.db --template-dir=mytemplates/

Datasette will now first look for templates in that directory, and fall back on the defaults if no matches are found.

It is also possible to over-ride templates on a per-database, per-row or per- table basis.

The lookup rules Datasette uses are as follows:

Index page (/):
    index.html

Database page (/mydatabase):
    database-mydatabase.html
    database.html

Custom query page (/mydatabase?sql=...):
    query-mydatabase.html
    query.html

Canned query page (/mydatabase/canned-query):
    query-mydatabase-canned-query.html
    query-mydatabase.html
    query.html

Table page (/mydatabase/mytable):
    table-mydatabase-mytable.html
    table.html

Row page (/mydatabase/mytable/id):
    row-mydatabase-mytable.html
    row.html

Table of rows and columns include on table page:
    _table-table-mydatabase-mytable.html
    _table-mydatabase-mytable.html
    _table.html

Table of rows and columns include on row page:
    _table-row-mydatabase-mytable.html
    _table-mydatabase-mytable.html
    _table.html

If a table name has spaces or other unexpected characters in it, the template filename will follow the same rules as our custom <body> CSS classes - for example, a table called "Food Trucks" will attempt to load the following templates:

table-mydatabase-Food-Trucks-399138.html
table.html

You can find out which templates were considered for a specific page by viewing source on that page and looking for an HTML comment at the bottom. The comment will look something like this:

<!-- Templates considered: *query-mydb-tz.html, query-mydb.html, query.html -->

This example is from the canned query page for a query called "tz" in the database called "mydb". The asterisk shows which template was selected - so in this case, Datasette found a template file called query-mydb-tz.html and used that - but if that template had not been found, it would have tried for query-mydb.html or the default query.html.

It is possible to extend the default templates using Jinja template inheritance. If you want to customize EVERY row template with some additional content you can do so by creating a row.html template like this:

{% extends "default:row.html" %}

{% block content %}
<h1>EXTRA HTML AT THE TOP OF THE CONTENT BLOCK</h1>
<p>This line renders the original block:</p>
{{ super() }}
{% endblock %}

Note the default:row.html template name, which ensures Jinja will inherit from the default template.

The _table.html template is included by both the row and the table pages, and a list of rows. The default _table.html template renders them as an HTML template and can be seen here.

You can provide a custom template that applies to all of your databases and tables, or you can provide custom templates for specific tables using the template naming scheme described above.

If you want to present your data in a format other than an HTML table, you can do so by looping through display_rows in your own _table.html template. You can use {{ row["column_name"] }} to output the raw value of a specific column.

If you want to output the rendered HTML version of a column, including any links to foreign keys, you can use {{ row.display("column_name") }}.

Here is an example of a custom _table.html template:

{% for row in display_rows %}
    <div>
        <h2>{{ row["title"] }}</h2>
        <p>{{ row["description"] }}<lp>
        <p>Category: {{ row.display("category_id") }}</p>
    </div>
{% endfor %}

Custom pages

You can add templated pages to your Datasette instance by creating HTML files in a pages directory within your templates directory.

For example, to add a custom page that is served at http://localhost/about you would create a file in templates/pages/about.html, then start Datasette like this:

datasette mydb.db --template-dir=templates/

You can nest directories within pages to create a nested structure. To create a http://localhost:8001/about/map page you would create templates/pages/about/map.html.

Path parameters for pages

You can define custom pages that match multiple paths by creating files with {variable} definitions in their filenames.

For example, to capture any request to a URL matching /about/*, you would create a template in the following location:

templates/pages/about/{slug}.html

A hit to /about/news would render that template and pass in a variable called slug with a value of "news".

If you use this mechanism don't forget to return a 404 if the referenced content could not be found. You can do this using {{ raise_404() }} described below.

Templates defined using custom page routes work particularly well with the sql() template function from datasette-template-sql or the graphql() template function from datasette-graphql.

Custom headers and status codes

Custom pages default to being served with a content-type of text/html; charset=utf-8 and a 200 status code. You can change these by calling a custom function from within your template.

For example, to serve a custom page with a 418 I'm a teapot HTTP status code, create a file in pages/teapot.html containing the following:

{{ custom_status(418) }}
<html>
<head><title>Teapot</title></head>
<body>
I'm a teapot
</body>
</html>

To serve a custom HTTP header, add a custom_header(name, value) function call. For example:

{{ custom_status(418) }}
{{ custom_header("x-teapot", "I am") }}
<html>
<head><title>Teapot</title></head>
<body>
I'm a teapot
</body>
</html>

You can verify this is working using curl like this:

curl -I 'http://127.0.0.1:8001/teapot'
HTTP/1.1 418
date: Sun, 26 Apr 2020 18:38:30 GMT
server: uvicorn
x-teapot: I am
content-type: text/html; charset=utf-8

Returning 404s

To indicate that content could not be found and display the default 404 page you can use the raise_404(message) function:

{% if not rows %}
    {{ raise_404("Content not found") }}
{% endif %}

If you call raise_404() the other content in your template will be ignored.

Custom redirects

You can use the custom_redirect(location) function to redirect users to another page, for example in a file called pages/datasette.html:

{{ custom_redirect("https://github.com/simonw/datasette") }}

Now requests to http://localhost:8001/datasette will result in a redirect.

These redirects are served with a 302 Found status code by default. You can send a 301 Moved Permanently code by passing 301 as the second argument to the function:

{{ custom_redirect("https://github.com/simonw/datasette", 301) }}

Custom error pages

Datasette returns an error page if an unexpected error occurs, access is forbidden or content cannot be found.

You can customize the response returned for these errors by providing a custom error page template.

Content not found errors use a 404.html template. Access denied errors use 403.html. Invalid input errors use 400.html. Unexpected errors of other kinds use 500.html.

If a template for the specific error code is not found a template called error.html will be used instead. If you do not provide that template Datasette's default error.html template will be used.

The error template will be passed the following context:

status - integer

The integer HTTP status code, e.g. 404, 500, 403, 400.

error - string

Details of the specific error, usually a full sentence.

title - string or None

A title for the page representing the class of error. This is often None for errors that do not provide a title separate from their error message.