From f35e4e6662abeb8fae05408d315bd9b526943870 Mon Sep 17 00:00:00 2001
From: Simon Willison <swillison@gmail.com>
Date: Sun, 30 Jun 2019 09:42:20 -0700
Subject: [PATCH] Initial sketch for index-foreign-keys, refs #33

---
 sqlite_utils/cli.py | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/sqlite_utils/cli.py b/sqlite_utils/cli.py
index 0df540a..ea7d193 100644
--- a/sqlite_utils/cli.py
+++ b/sqlite_utils/cli.py
@@ -217,6 +217,31 @@ def add_foreign_key(path, table, column, other_table, other_column):
         raise click.ClickException(e)
 
 
+
+@cli.command(name="index-foreign-keys")
+@click.argument(
+    "path",
+    type=click.Path(exists=True, file_okay=True, dir_okay=False, allow_dash=False),
+    required=True,
+)
+def index_foreign_keys(path):
+    """
+    Ensure every foreign key column has an index on it.
+    """
+    db = sqlite_utils.Database(path)
+    for table_name in db.table_names():
+        table = db[table_name]
+        existing_indexes = {
+            i.columns[0] for i in table.indexes if len(i.columns) == 1
+        }
+        for fk in table.foreign_keys:
+            if fk.column not in existing_indexes:
+                print("Creating index on {}.{}".format(
+                    table_name, fk.column
+                ))
+                table.create_index([fk.column])
+
+
 @cli.command(name="create-index")
 @click.argument(
     "path",