Support self-referencing FKs in create (#537)

sqlite_utils/db.py

@@ -813,6 +813,8 @@ class Database:
             pk = hash_id
         # Soundness check foreign_keys point to existing tables
         for fk in foreign_keys:
+            if fk.other_table == name and columns.get(fk.other_column):
+                continue
             if not any(
                 c for c in self[fk.other_table].columns if c.name == fk.other_column
             ):

tests/test_create.py

@@ -288,6 +288,25 @@ def test_create_table_works_for_m2m_with_only_foreign_keys(
     )
 
 
+def test_self_referential_foreign_key(fresh_db):
+    assert [] == fresh_db.table_names()
+    table = fresh_db.create_table(
+        "test_table",
+        columns={
+            "id": int,
+            "ref": int,
+        },
+        pk="id",
+        foreign_keys=(("ref", "test_table", "id"),),
+    )
+    assert (
+        "CREATE TABLE [test_table] (\n"
+        "   [id] INTEGER PRIMARY KEY,\n"
+        "   [ref] INTEGER REFERENCES [test_table]([id])\n"
+        ")"
+    ) == table.schema
+
+
 def test_create_error_if_invalid_foreign_keys(fresh_db):
     with pytest.raises(AlterError):
         fresh_db["one"].insert(
@@ -297,6 +316,15 @@ def test_create_error_if_invalid_foreign_keys(fresh_db):
         )
 
 
+def test_create_error_if_invalid_self_referential_foreign_keys(fresh_db):
+    with pytest.raises(AlterError):
+        fresh_db["one"].insert(
+            {"id": 1, "ref_id": 3},
+            pk="id",
+            foreign_keys=(("ref_id", "one", "bad_column"),),
+        )
+
+
 @pytest.mark.parametrize(
     "col_name,col_type,not_null_default,expected_schema",
     (