From faf33515b2e6ef8b891e7c9693c66aba2a77dc54 Mon Sep 17 00:00:00 2001
From: Simon Willison <swillison@gmail.com>
Date: Wed, 15 May 2019 20:23:33 -0700
Subject: [PATCH] Sometimes sort tables by number of relationships, closes #460

---
 datasette/app.py            |  6 ++++++
 datasette/views/database.py |  4 +---
 datasette/views/index.py    | 15 ++++++++++++++-
 tests/test_api.py           | 15 +++++++++++++++
 4 files changed, 36 insertions(+), 4 deletions(-)

diff --git a/datasette/app.py b/datasette/app.py
index c2bf330f..db771e40 100644
--- a/datasette/app.py
+++ b/datasette/app.py
@@ -30,6 +30,7 @@ from .utils import (
     detect_spatialite,
     escape_css_string,
     escape_sqlite,
+    get_all_foreign_keys,
     get_outbound_foreign_keys,
     get_plugins,
     module_from_path,
@@ -261,6 +262,11 @@ class ConnectedDatabase:
         )
         return [r[0] for r in results.rows]
 
+    async def get_all_foreign_keys(self):
+        return await self.ds.execute_against_connection_in_thread(
+            self.name, get_all_foreign_keys
+        )
+
     def __repr__(self):
         tags = []
         if self.is_mutable:
diff --git a/datasette/views/database.py b/datasette/views/database.py
index 5fab04b0..5065b90f 100644
--- a/datasette/views/database.py
+++ b/datasette/views/database.py
@@ -29,9 +29,7 @@ class DatabaseView(BaseView):
         table_counts = await db.table_counts(5)
         views = await db.view_names()
         hidden_table_names = set(await db.hidden_table_names())
-        all_foreign_keys = await self.ds.execute_against_connection_in_thread(
-            database, get_all_foreign_keys
-        )
+        all_foreign_keys = await db.get_all_foreign_keys()
 
         metadata = (self.ds.metadata("databases") or {}).get(database, {})
         self.ds.update_with_inherited_metadata(metadata)
diff --git a/datasette/views/index.py b/datasette/views/index.py
index bca901f5..d3d82bae 100644
--- a/datasette/views/index.py
+++ b/datasette/views/index.py
@@ -54,14 +54,27 @@ class IndexView(RenderMixin):
                     "fts_table": await self.ds.execute_against_connection_in_thread(
                         name, lambda conn: detect_fts(conn, table)
                     ),
+                    "num_relationships_for_sorting": 0,
                 }
+
+            if request.args.get("_sort") == "relationships" or not table_counts:
+                # We will be sorting by number of relationships, so populate that field
+                all_foreign_keys = await db.get_all_foreign_keys()
+                for table, foreign_keys in all_foreign_keys.items():
+                    count = len(foreign_keys["incoming"] + foreign_keys["outgoing"])
+                    tables[table]["num_relationships_for_sorting"] = count
+
             hidden_tables = [t for t in tables.values() if t["hidden"]]
             visible_tables = [t for t in tables.values() if not t["hidden"]]
 
             tables_and_views_truncated = list(
                 sorted(
                     (t for t in tables.values() if t not in hidden_tables),
-                    key=lambda t: t["count"] or 0,
+                    key=lambda t: (
+                        t["num_relationships_for_sorting"],
+                        t["count"] or 0,
+                        t["name"],
+                    ),
                     reverse=True,
                 )[:TRUNCATE_AT]
             )
diff --git a/tests/test_api.py b/tests/test_api.py
index ea5d2a2d..b4599ab3 100644
--- a/tests/test_api.py
+++ b/tests/test_api.py
@@ -34,6 +34,21 @@ def test_homepage(app_client):
     assert d["views_count"] == 4
 
 
+def test_homepage_sort_by_relationships(app_client):
+    response = app_client.get("/.json?_sort=relationships")
+    assert response.status == 200
+    tables = [
+        t["name"] for t in response.json["fixtures"]["tables_and_views_truncated"]
+    ]
+    assert [
+        "simple_primary_key",
+        "complex_foreign_keys",
+        "searchable_tags",
+        "foreign_key_references",
+        "facetable",
+    ] == tables
+
+
 def test_database_page(app_client):
     response = app_client.get("/fixtures.json")
     data = response.json