kopia lustrzana https://github.com/simonw/datasette
119 wiersze
4.2 KiB
ReStructuredText
119 wiersze
4.2 KiB
ReStructuredText
.. _facets:
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Facets
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======
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Datasette facets can be used to add a faceted browse interface to any Datasette table. With facets, tables are displayed along with a summary showing the most common values in specified columns. These values can be selected to further filter the table.
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Facets can be specified in two ways: using queryset parameters, or in ``metadata.json`` configuration for the table.
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Facets in querystrings
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----------------------
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To turn on faceting for specific columns on a Datasette table view, add one or more ``_facet=COLUMN`` parameters to the URL. For example, if you want to turn on facets for the ``city`` and ``state`` columns, construct a URL that looks like this::
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/dbname/tablename?_facet=state&_facet=city
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This works for both the HTML interface and the ``.json`` view. When enabled, facets will cause a ``facet_results`` block to be added to the JSON output, looking something like this::
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{
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"state": {
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"name": "state",
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"results": [
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{
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"value": "CA",
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"label": "CA",
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"count": 10,
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"toggle_url": "http://...?_facet=city_id&_facet=state&state=CA",
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"selected": false
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},
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{
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"value": "MI",
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"label": "MI",
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"count": 4,
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"toggle_url": "http://...?_facet=city_id&_facet=state&state=MI",
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"selected": false
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},
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{
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"value": "MC",
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"label": "MC",
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"count": 1,
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"toggle_url": "http://...?_facet=city_id&_facet=state&state=MC",
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"selected": false
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}
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],
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"truncated": false
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}
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"city_id": {
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"name": "city_id",
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"results": [
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{
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"value": 1,
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"label": "San Francisco",
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"count": 6,
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"toggle_url": "http://...?_facet=city_id&_facet=state&city_id=1",
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"selected": false
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},
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{
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"value": 2,
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"label": "Los Angeles",
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"count": 4,
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"toggle_url": "http://...?_facet=city_id&_facet=state&city_id=2",
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"selected": false
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},
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{
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"value": 3,
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"label": "Detroit",
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"count": 4,
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"toggle_url": "http://...?_facet=city_id&_facet=state&city_id=3",
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"selected": false
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},
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{
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"value": 4,
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"label": "Memnonia",
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"count": 1,
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"toggle_url": "http://...?_facet=city_id&_facet=state&city_id=4",
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"selected": false
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}
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],
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"truncated": false
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}
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}
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If Datasette detects that a column is a foreign key, the ``"label"`` proper will be automatically derived from the detected label column on the referenced table.
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Facets in metadata.json
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-----------------------
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You can turn facets on by default for specific tables by adding them to a ``"facets"`` key in a Datasette :ref:`metadata` file.
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Here's an example that turns on faceting by default for the ``qLegalStatus`` column in the ``Street_Tree_List`` table in the ``sf-trees`` database::
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{
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"databases": {
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"sf-trees": {
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"tables": {
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"Street_Tree_List": {
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"facets": ["qLegalStatus"]
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}
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}
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}
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}
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}
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Facets defined in this way will always be shown in the interface and returned in the API, regardless of the ``_facet`` arguments passed to the view.
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Suggested facets
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----------------
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Datasette's table UI will suggest facets for the user to apply, based on the following criteria:
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For the currently filtered data are there any columns which, if applied as a facet...
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* Will return 20 or less unique options
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* Will return more than one unique option
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* Will return less unique options than the total number of filtered rows
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* And the query used to evaluate this criteria can be completed in under 20ms
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That last point is particularly important: Datasette runs a query for every column that is displayed on a page, which could get expensive - so to avoid slow load times it sets a time limit of just 20ms for each of those queries. This means suggested facets are unlikely to appear for tables with millions of records in them.
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