Expose foreign key data to alter table UI

Include current foreign key metadata in the alter table page data and allow the foreign-key-targets endpoint to be read by actors with alter-table permission for a specific table.

Add API and HTML data tests for the new alter-table foreign key support.

datasette/views/table.py

@@ -382,6 +382,19 @@ async def _table_alter_ui(
         return None
 
     column_types_map = await datasette.get_column_types(database_name, table_name)
+    foreign_keys_by_column = {}
+    for fk in await db.foreign_keys_for_table(table_name):
+        other_column = fk["other_column"]
+        if other_column is None and await db.table_exists(fk["other_table"]):
+            other_pks = await db.primary_keys(fk["other_table"])
+            if len(other_pks) == 1:
+                other_column = other_pks[0]
+        if other_column is None:
+            continue
+        foreign_keys_by_column[fk["column"]] = {
+            "fk_table": fk["other_table"],
+            "fk_column": other_column,
+        }
     columns = []
     for column in await db.table_column_details(table_name):
         if column.hidden:
@@ -397,6 +410,7 @@ async def _table_alter_ui(
                 "default": column.default_value,
                 "has_default": column.default_value is not None,
                 "is_pk": column.name in pks,
+                "foreign_key": foreign_keys_by_column.get(column.name),
                 "column_type": (
                     {"type": column_type.name, "config": column_type.config}
                     if column_type is not None
@@ -412,6 +426,10 @@ async def _table_alter_ui(
         "primaryKeys": pks,
         "columnTypes": ALTER_TABLE_COLUMN_TYPES,
         "defaultExpressions": list(DEFAULT_EXPR_SQL),
+        "foreignKeyTargetsPath": "{}/-/foreign-key-targets?table={}".format(
+            datasette.urls.database(database_name),
+            urllib.parse.quote(table_name, safe=""),
+        ),
     }
     can_set_column_type = await datasette.allowed(
         action="set-column-type",

datasette/views/table_create_alter.py

@@ -867,11 +867,20 @@ class DatabaseForeignKeyTargetsView(BaseView):
         db = await self.ds.resolve_database(request)
         database_name = db.name
 
-        if not await self.ds.allowed(
+        table_name = request.args.get("table")
+        can_create_table = await self.ds.allowed(
             action="create-table",
             resource=DatabaseResource(database=database_name),
             actor=request.actor,
-        ):
+        )
+        can_alter_table = False
+        if table_name and await db.table_exists(table_name):
+            can_alter_table = await self.ds.allowed(
+                action="alter-table",
+                resource=TableResource(database=database_name, table=table_name),
+                actor=request.actor,
+            )
+        if not (can_create_table or can_alter_table):
             return _error(["Permission denied: need create-table"], 403)
 
         hidden_tables = await db.execute_fn(

tests/test_api_write.py

@@ -1252,6 +1252,17 @@ async def test_foreign_key_targets_permission_denied(ds_write):
     }
 
 
+@pytest.mark.asyncio
+async def test_foreign_key_targets_allowed_for_alter_table(ds_write):
+    token = write_token(ds_write, permissions=["at"])
+    response = await ds_write.client.get(
+        "/data/-/foreign-key-targets?table=docs",
+        headers=_headers(token),
+    )
+    assert response.status_code == 200, response.text
+    assert response.json()["ok"] is True
+
+
 @pytest.mark.asyncio
 async def test_alter_table_permission_denied(ds_write):
     token = write_token(ds_write, permissions=["ir"])

tests/test_table_html.py

@@ -1137,6 +1137,9 @@ async def test_table_alter_action_button_and_data():
         assert alter_data["tableName"] == "items"
         assert alter_data["primaryKeys"] == ["id"]
         assert alter_data["columnTypes"] == ["text", "integer", "float", "blob"]
+        assert alter_data["foreignKeyTargetsPath"] == (
+            "/data/-/foreign-key-targets?table=items"
+        )
         assert alter_data["defaultExpressions"] == [
             "current_timestamp",
             "current_date",
@@ -1158,6 +1161,7 @@ async def test_table_alter_action_button_and_data():
                 "default": None,
                 "has_default": False,
                 "is_pk": True,
+                "foreign_key": None,
                 "column_type": None,
             },
             {
@@ -1168,6 +1172,7 @@ async def test_table_alter_action_button_and_data():
                 "default": None,
                 "has_default": False,
                 "is_pk": False,
+                "foreign_key": None,
                 "column_type": {"type": "textarea", "config": None},
             },
             {
@@ -1178,6 +1183,7 @@ async def test_table_alter_action_button_and_data():
                 "default": "5",
                 "has_default": True,
                 "is_pk": False,
+                "foreign_key": None,
                 "column_type": None,
             },
         ]