Update get execution's tasks functionality

After this patch, it will validate execution-id exists in the DB while fetching tasks for the execution-id So, GET /v2/executions/execution_id/tasks API will return 404 for absent execution id.

Closes-Bug: #1998210
Change-Id: I6ac05f4b87c470a68cd67f19d1bd95a4d6cebe59

mistral/api/controllers/v2/task.py

@@ -28,6 +28,7 @@ from mistral.api.controllers.v2 import sub_execution
 from mistral.api.controllers.v2 import types
 from mistral import context
 from mistral.db.v2 import api as db_api
+from mistral.db.v2.sqlalchemy import models as db_models
 from mistral import exceptions as exc
 from mistral import expressions as expr
 from mistral.lang import parser as spec_parser
@@ -440,6 +441,12 @@ class ExecutionTasksController(rest.RestController):
         """
         acl.enforce('tasks:list', context.ctx())
 
+        with db_api.transaction():
+            db_api.get_workflow_execution(
+                workflow_execution_id,
+                fields=(db_models.WorkflowExecution.id,)
+            )
+
         filters = filter_utils.create_filters_from_request_params(
             workflow_execution_id=workflow_execution_id,
             created_at=created_at,

mistral/tests/unit/api/v2/test_executions.py

@@ -994,3 +994,17 @@ class TestExecutionsController(base.APITest):
             "The field 'id' can't hold None value.",
             resp.body.decode()
         )
+
+    @mock.patch.object(db_api, 'get_workflow_execution', MOCK_NOT_FOUND)
+    def test_get_all_tasks_within_execution(self):
+        fake_execution_id = "00000000-0000-0000-0000-000000000000"
+        resp = self.app.get(
+            '/v2/executions/%s/tasks' % fake_execution_id,
+            expect_errors=True
+        )
+
+        self.assertEqual(404, resp.status_int)
+        self.assertIn(
+            "Object not found",
+            resp.body.decode()
+        )