Unit test + bug fix for db.add_foreign_keys()

sqlite_utils/db.py

@@ -287,24 +287,24 @@ class Database:
                     (table, column, other_table, other_column)
                 )
 
-        # Construct list of args to be used with "UPDATE sqlite_master SET sql = ? WHERE name = ?"
-        sql_args = []
+        # Construct SQL for use with "UPDATE sqlite_master SET sql = ? WHERE name = ?"
+        table_sql = {}
         for table, column, other_table, other_column in foreign_keys:
-            old_sql = self[table].schema
+            old_sql = table_sql.get(table, self[table].schema)
             extra_sql = ",\n   FOREIGN KEY({column}) REFERENCES {other_table}({other_column})\n".format(
                 column=column, other_table=other_table, other_column=other_column
             )
             # Stick that bit in at the very end just before the closing ')'
             last_paren = old_sql.rindex(")")
             new_sql = old_sql[:last_paren].strip() + extra_sql + old_sql[last_paren:]
-            sql_args.append((new_sql, table))
+            table_sql[table] = new_sql
 
         # And execute it all within a single transaction
         with self.conn:
             cursor = self.conn.cursor()
             schema_version = cursor.execute("PRAGMA schema_version").fetchone()[0]
             cursor.execute("PRAGMA writable_schema = 1")
-            for new_sql, table_name in sql_args:
+            for table_name, new_sql in table_sql.items():
                 cursor.execute(
                     "UPDATE sqlite_master SET sql = ? WHERE name = ?",
                     (new_sql, table_name),

tests/test_create.py

@@ -303,6 +303,34 @@ def test_add_foreign_key_error_if_already_exists(fresh_db):
     assert "Foreign key already exists for author_id => authors.id" == ex.value.args[0]
 
 
+def test_add_foreign_keys(fresh_db):
+    fresh_db["authors"].insert_all(
+        [{"id": 1, "name": "Sally"}, {"id": 2, "name": "Asheesh"}], pk="id"
+    )
+    fresh_db["categories"].insert_all([{"id": 1, "name": "Wildlife"}], pk="id")
+    fresh_db["books"].insert_all(
+        [{"title": "Hedgehogs of the world", "author_id": 1, "category_id": 1}]
+    )
+    assert [] == fresh_db["books"].foreign_keys
+    fresh_db.add_foreign_keys(
+        [
+            ("books", "author_id", "authors", "id"),
+            ("books", "category_id", "categories", "id"),
+        ]
+    )
+    assert [
+        ForeignKey(
+            table="books", column="author_id", other_table="authors", other_column="id"
+        ),
+        ForeignKey(
+            table="books",
+            column="category_id",
+            other_table="categories",
+            other_column="id",
+        ),
+    ] == sorted(fresh_db["books"].foreign_keys)
+
+
 def test_add_column_foreign_key(fresh_db):
     fresh_db.create_table("dogs", {"name": str})
     fresh_db.create_table("breeds", {"name": str})