`__.
Specifying units for a column
-----------------------------
Datasette supports attaching units to a column, which will be used when displaying
values from that column. SI prefixes will be used where appropriate.
Column units are configured in the metadata like so:
.. code-block:: json
{
"databases": {
"database1": {
"tables": {
"example_table": {
"units": {
"column1": "metres",
"column2": "Hz"
}
}
}
}
}
}
Units are interpreted using Pint_, and you can see the full list of available units in
Pint's `unit registry`_. You can also add `custom units`_ to the metadata, which will be
registered with Pint:
.. code-block:: json
{
"custom_units": [
"decibel = [] = dB"
]
}
.. _Pint: https://pint.readthedocs.io/
.. _unit registry: https://github.com/hgrecco/pint/blob/master/pint/default_en.txt
.. _custom units: http://pint.readthedocs.io/en/latest/defining.html
.. _metadata_default_sort:
Setting a default sort order
----------------------------
By default Datasette tables are sorted by primary key. You can over-ride this default for a specific table using the ``"sort"`` or ``"sort_desc"`` metadata properties:
.. code-block:: json
{
"databases": {
"mydatabase": {
"tables": {
"example_table": {
"sort": "created"
}
}
}
}
}
Or use ``"sort_desc"`` to sort in descending order:
.. code-block:: json
{
"databases": {
"mydatabase": {
"tables": {
"example_table": {
"sort_desc": "created"
}
}
}
}
}
.. _metadata_page_size:
Setting a custom page size
--------------------------
Datasette defaults to displaing 100 rows per page, for both tables and views. You can change this default page size on a per-table or per-view basis using the ``"size"`` key in ``metadata.json``:
.. code-block:: json
{
"databases": {
"mydatabase": {
"tables": {
"example_table": {
"size": 10
}
}
}
}
}
This size can still be over-ridden by passing e.g. ``?_size=50`` in the query string.
.. _metadata_sortable_columns:
Setting which columns can be used for sorting
---------------------------------------------
Datasette allows any column to be used for sorting by default. If you need to
control which columns are available for sorting you can do so using the optional
``sortable_columns`` key:
.. code-block:: json
{
"databases": {
"database1": {
"tables": {
"example_table": {
"sortable_columns": [
"height",
"weight"
]
}
}
}
}
}
This will restrict sorting of ``example_table`` to just the ``height`` and
``weight`` columns.
You can also disable sorting entirely by setting ``"sortable_columns": []``
You can use ``sortable_columns`` to enable specific sort orders for a view called ``name_of_view`` in the database ``my_database`` like so:
.. code-block:: json
{
"databases": {
"my_database": {
"tables": {
"name_of_view": {
"sortable_columns": [
"clicks",
"impressions"
]
}
}
}
}
}
.. _label_columns:
Specifying the label column for a table
---------------------------------------
Datasette's HTML interface attempts to display foreign key references as
labelled hyperlinks. By default, it looks for referenced tables that only have
two columns: a primary key column and one other. It assumes that the second
column should be used as the link label.
If your table has more than two columns you can specify which column should be
used for the link label with the ``label_column`` property:
.. code-block:: json
{
"databases": {
"database1": {
"tables": {
"example_table": {
"label_column": "title"
}
}
}
}
}
.. _metadata_hiding_tables:
Hiding tables
-------------
You can hide tables from the database listing view (in the same way that FTS and
SpatiaLite tables are automatically hidden) using ``"hidden": true``:
.. code-block:: json
{
"databases": {
"database1": {
"tables": {
"example_table": {
"hidden": true
}
}
}
}
}
.. _metadata_yaml:
Using YAML for metadata
-----------------------
Datasette accepts YAML as an alternative to JSON for your metadata configuration file. YAML is particularly useful for including multiline HTML and SQL strings.
Here's an example of a ``metadata.yml`` file, re-using an example from :ref:`canned_queries`.
.. code-block:: yaml
title: Demonstrating Metadata from YAML
description_html: |-
This description includes a long HTML string
- YAML is better for embedding HTML strings than JSON!
license: ODbL
license_url: https://opendatacommons.org/licenses/odbl/
databases:
fixtures:
tables:
no_primary_key:
hidden: true
queries:
neighborhood_search:
sql: |-
select neighborhood, facet_cities.name, state
from facetable join facet_cities on facetable.city_id = facet_cities.id
where neighborhood like '%' || :text || '%' order by neighborhood;
title: Search neighborhoods
description_html: |-
This demonstrates basic LIKE search
The ``metadata.yml`` file is passed to Datasette using the same ``--metadata`` option::
datasette fixtures.db --metadata metadata.yml