From a37ee74891f14898d5810127c7ca3355e77ff57d Mon Sep 17 00:00:00 2001
From: Simon Willison <swillison@gmail.com>
Date: Mon, 29 Nov 2021 22:34:31 -0800
Subject: [PATCH] Correct link to _ prefix on row page, closes #1525

---
 datasette/templates/row.html |  2 +-
 datasette/views/table.py     | 10 +++++++++-
 tests/test_html.py           | 28 ++++++++++++++++++++++++++++
 3 files changed, 38 insertions(+), 2 deletions(-)

diff --git a/datasette/templates/row.html b/datasette/templates/row.html
index 916980b6..c86e979d 100644
--- a/datasette/templates/row.html
+++ b/datasette/templates/row.html
@@ -38,7 +38,7 @@
     <ul>
         {% for other in foreign_key_tables %}
             <li>
-                <a href="{{ urls.table(database, other.other_table) }}?{{ other.other_column }}={{ ', '.join(primary_key_values) }}">
+                <a href="{{ other.link }}">
                     {{ "{:,}".format(other.count) }} row{% if other.count == 1 %}{% else %}s{% endif %}</a>
                 from {{ other.other_column }} in {{ other.other_table }}
             </li>
diff --git a/datasette/views/table.py b/datasette/views/table.py
index 9fc6afcf..f58b78f5 100644
--- a/datasette/views/table.py
+++ b/datasette/views/table.py
@@ -1120,5 +1120,13 @@ class RowView(RowTableShared):
             count = (
                 foreign_table_counts.get((fk["other_table"], fk["other_column"])) or 0
             )
-            foreign_key_tables.append({**fk, **{"count": count}})
+            key = fk["other_column"]
+            if key.startswith("_"):
+                key += "__exact"
+            link = "{}?{}={}".format(
+                self.ds.urls.table(database, fk["other_table"]),
+                key,
+                ",".join(pk_values),
+            )
+            foreign_key_tables.append({**fk, **{"count": count, "link": link}})
         return foreign_key_tables
diff --git a/tests/test_html.py b/tests/test_html.py
index aaf7da09..a7cb105c 100644
--- a/tests/test_html.py
+++ b/tests/test_html.py
@@ -820,6 +820,34 @@ def test_row_html_no_primary_key(app_client):
     ]
 
 
+@pytest.mark.parametrize(
+    "path,expected_text,expected_link",
+    (
+        (
+            "/fixtures/facet_cities/1",
+            "6 rows from _city_id in facetable",
+            "/fixtures/facetable?_city_id__exact=1",
+        ),
+        (
+            "/fixtures/attraction_characteristic/2",
+            "3 rows from characteristic_id in roadside_attraction_characteristics",
+            "/fixtures/roadside_attraction_characteristics?characteristic_id=2",
+        ),
+    ),
+)
+def test_row_links_from_other_tables(app_client, path, expected_text, expected_link):
+    response = app_client.get(path)
+    assert response.status == 200
+    soup = Soup(response.body, "html.parser")
+    h2 = soup.find("h2")
+    assert h2.text == "Links from other tables"
+    li = h2.findNext("ul").find("li")
+    text = re.sub(r"\s+", " ", li.text.strip())
+    assert text == expected_text
+    link = li.find("a")["href"]
+    assert link == expected_link
+
+
 def test_table_html_compound_primary_key(app_client):
     response = app_client.get("/fixtures/compound_primary_key")
     assert response.status == 200