render_cell(value) plugin hook, closes #352

New plugin hook for customizing the way cells values are rendered in HTML.

The first full example of this hook in use is https://github.com/simonw/datasette-json-html

datasette/app.py

@@ -2,7 +2,6 @@ import asyncio
 import click
 import collections
 import hashlib
-import importlib
 import itertools
 import os
 import sqlite3
@@ -14,7 +13,6 @@ from concurrent import futures
 from pathlib import Path
 
 from markupsafe import Markup
-import pluggy
 from jinja2 import ChoiceLoader, Environment, FileSystemLoader, PrefixLoader
 from sanic import Sanic, response
 from sanic.exceptions import InvalidUsage, NotFound
@@ -28,7 +26,6 @@ from .views.index import IndexView
 from .views.special import JsonDataView
 from .views.table import RowView, TableView
 
-from . import hookspecs
 from .utils import (
     InterruptedError,
     Results,
@@ -40,26 +37,13 @@ from .utils import (
     to_css_class
 )
 from .inspect import inspect_hash, inspect_views, inspect_tables
+from .plugins import pm
 from .version import __version__
 
-default_plugins = (
-    "datasette.publish.heroku",
-    "datasette.publish.now",
-)
-
 app_root = Path(__file__).parent.parent
 
 connections = threading.local()
 
-pm = pluggy.PluginManager("datasette")
-pm.add_hookspecs(hookspecs)
-pm.load_setuptools_entrypoints("datasette")
-
-# Load default plugins
-for plugin in default_plugins:
-    mod = importlib.import_module(plugin)
-    pm.register(mod, plugin)
-
 
 ConfigOption = collections.namedtuple(
     "ConfigOption", ("name", "default", "help")

datasette/hookspecs.py

@@ -28,3 +28,8 @@ def extra_js_urls():
 @hookspec
 def publish_subcommand(publish):
     "Subcommands for 'datasette publish'"
+
+
+@hookspec(firstresult=True)
+def render_cell(value):
+    "Customize rendering of HTML table cell values"

datasette/plugins.py

@@ -0,0 +1,17 @@
+import importlib
+import pluggy
+from . import hookspecs
+
+default_plugins = (
+    "datasette.publish.heroku",
+    "datasette.publish.now",
+)
+
+pm = pluggy.PluginManager("datasette")
+pm.add_hookspecs(hookspecs)
+pm.load_setuptools_entrypoints("datasette")
+
+# Load default plugins
+for plugin in default_plugins:
+    mod = importlib.import_module(plugin)
+    pm.register(mod, plugin)

datasette/utils.py

@@ -16,7 +16,6 @@ import shutil
 import urllib
 import numbers
 
-
 # From https://www.sqlite.org/lang_keywords.html
 reserved_words = set((
     'abort action add after all alter analyze and as asc attach autoincrement '

datasette/views/base.py

@@ -13,6 +13,7 @@ from sanic.exceptions import NotFound
 from sanic.views import HTTPMethodView
 
 from datasette import __version__
+from datasette.plugins import pm
 from datasette.utils import (
     CustomJSONEncoder,
     InterruptedError,
@@ -493,14 +494,19 @@ class BaseView(RenderMixin):
                 display_row = []
                 for value in row:
                     display_value = value
-                    if value in ("", None):
-                        display_value = jinja2.Markup(" ")
-                    elif is_url(str(value).strip()):
-                        display_value = jinja2.Markup(
-                            '<a href="{url}">{url}</a>'.format(
-                                url=jinja2.escape(value.strip())
+                    # Let the plugins have a go
+                    plugin_value = pm.hook.render_cell(value=value)
+                    if plugin_value is not None:
+                        display_value = plugin_value
+                    else:
+                        if value in ("", None):
+                            display_value = jinja2.Markup("&nbsp;")
+                        elif is_url(str(display_value).strip()):
+                            display_value = jinja2.Markup(
+                                '<a href="{url}">{url}</a>'.format(
+                                    url=jinja2.escape(value.strip())
+                                )
                             )
-                        )
                     display_row.append(display_value)
                 display_rows.append(display_row)
             return {

datasette/views/table.py

@@ -5,6 +5,7 @@ import jinja2
 from sanic.exceptions import NotFound
 from sanic.request import RequestParameters
 
+from datasette.plugins import pm
 from datasette.utils import (
     CustomRow,
     Filters,
@@ -22,7 +23,6 @@ from datasette.utils import (
     urlsafe_components,
     value_as_boolean,
 )
-
 from .base import BaseView, DatasetteError, ureg
 
 LINK_WITH_LABEL = '<a href="/{database}/{table}/{link_id}">{label}</a>&nbsp;<em>{id}</em>'
@@ -166,7 +166,11 @@ class RowTableShared(BaseView):
                     # already shown in the link column.
                     continue
 
-                if isinstance(value, dict):
+                # First let the plugins have a go
+                plugin_display_value = pm.hook.render_cell(value=value)
+                if plugin_display_value is not None:
+                    display_value = plugin_display_value
+                elif isinstance(value, dict):
                     # It's an expanded foreign key - display link to other row
                     label = value["label"]
                     value = value["value"]

docs/plugins.rst

@@ -267,3 +267,56 @@ command. Datasette uses this hook internally to implement the default ``now``
 and ``heroku`` subcommands, so you can read
 `their source <https://github.com/simonw/datasette/tree/master/datasette/publish>`_
 to see examples of this hook in action.
+
+render_cell(value)
+~~~~~~~~~~~~~~~~~~
+
+Lets you customize the display of values within table cells in the HTML table view.
+
+``value`` is the value that was loaded from the database.
+
+If your hook returns ``None``, it will be ignored. Use this to indicate that your hook is not able to custom render this particular value.
+
+If the hook returns a string, that string will be rendered in the table cell.
+
+If you want to return HTML markup you can do so by returning a ``jinja2.Markup`` object.
+
+Here is an example of a custom ``render_cell()`` plugin which looks for values that are a JSON string matching the following format::
+
+    {"href": "https://www.example.com/", "label": "Name"}
+
+If the value matches that pattern, the plugin returns an HTML link element:
+
+.. code-block:: python
+
+    from datasette import hookimpl
+    import jinja2
+    import json
+
+
+    @hookimpl
+    def render_cell(value):
+        # Render {"href": "...", "label": "..."} as link
+        if not isinstance(value, str):
+            return None
+        stripped = value.strip()
+        if not stripped.startswith("{") and stripped.endswith("}"):
+            return None
+        try:
+            data = json.loads(value)
+        except ValueError:
+            return None
+        if not isinstance(data, dict):
+            return None
+        if set(data.keys()) != {"href", "label"}:
+            return None
+        href = data["href"]
+        if not (
+            href.startswith("/") or href.startswith("http://")
+            or href.startswith("https://")
+        ):
+            return None
+        return jinja2.Markup('<a href="{href}">{label}</a>'.format(
+            href=jinja2.escape(data["href"]),
+            label=jinja2.escape(data["label"] or "") or "&nbsp;"
+        ))

tests/fixtures.py

@@ -208,6 +208,8 @@ def extra_js_urls():
 
 PLUGIN2 = '''
 from datasette import hookimpl
+import jinja2
+import json
 
 
 @hookimpl
@@ -216,6 +218,34 @@ def extra_js_urls():
         'url': 'https://example.com/jquery.js',
         'sri': 'SRIHASH',
     }, 'https://example.com/plugin2.js']
+
+
+@hookimpl
+def render_cell(value):
+    # Render {"href": "...", "label": "..."} as link
+    if not isinstance(value, str):
+        return None
+    stripped = value.strip()
+    if not stripped.startswith("{") and stripped.endswith("}"):
+        return None
+    try:
+        data = json.loads(value)
+    except ValueError:
+        return None
+    if not isinstance(data, dict):
+        return None
+    if set(data.keys()) != {"href", "label"}:
+        return None
+    href = data["href"]
+    if not (
+        href.startswith("/") or href.startswith("http://")
+        or href.startswith("https://")
+    ):
+        return None
+    return jinja2.Markup('<a href="{href}">{label}</a>'.format(
+        href=jinja2.escape(data["href"]),
+        label=jinja2.escape(data["label"] or "") or "&nbsp;"
+    ))
 '''
 
 TABLES = '''
@@ -363,9 +393,12 @@ INSERT INTO "searchable_fts" (rowid, text1, text2, [name with . and spaces])
 CREATE TABLE [select] (
   [group] text,
   [having] text,
-  [and] text
+  [and] text,
+  [json] text
+);
+INSERT INTO [select] VALUES ('group', 'having', 'and',
+    '{"href": "http://example.com/", "label":"Example"}'
 );
-INSERT INTO [select] VALUES ('group', 'having', 'and');
 
 CREATE TABLE infinity (
     value REAL

tests/test_api.py

@@ -231,7 +231,7 @@ def test_database_page(app_client):
             ],
         },
     }, {
-        'columns': ['group', 'having', 'and'],
+        'columns': ['group', 'having', 'and', 'json'],
         'name': 'select',
         'count': 1,
         'hidden': False,
@@ -599,6 +599,7 @@ def test_table_with_reserved_word_name(app_client):
         'group': 'group',
         'having': 'having',
         'and': 'and',
+        'json': '{"href": "http://example.com/", "label":"Example"}'
     }]
 
 

tests/test_plugins.py

@@ -3,6 +3,7 @@ from .fixtures import ( # noqa
     app_client,
 )
 import pytest
+import urllib
 
 
 def test_plugins_dir_plugin(app_client):
@@ -67,3 +68,20 @@ def test_plugins_with_duplicate_js_urls(app_client):
     ) < srcs.index(
         'https://example.com/plugin2.js'
     )
+
+
+def test_plugins_render_cell(app_client):
+    sql = """
+        select '{"href": "http://example.com/", "label":"Example"}'
+    """.strip()
+    path = "/fixtures?" + urllib.parse.urlencode({
+        "sql": sql,
+    })
+    response = app_client.get(path)
+    td = Soup(
+        response.body, "html.parser"
+    ).find("table").find("tbody").find("td")
+    a = td.find("a")
+    assert a is not None, str(a)
+    assert a.attrs["href"] == "http://example.com/"
+    assert a.text == "Example"