defer commit of module entry until we set the context and validate

module_build_service/common/models.py

@@ -621,6 +621,7 @@ class ModuleBuild(MBSBase):
         rebuild_strategy=None,
         scratch=False,
         srpms=None,
+        commit=True,
         **kwargs
     ):
         now = datetime.utcnow()
@@ -650,7 +651,8 @@ class ModuleBuild(MBSBase):
             module.buildrequires.append(base_module)
 
         db_session.add(module)
-        db_session.commit()
+        if commit:
+            db_session.commit()
         return module
 
     def transition(self, db_session, conf, state, state_reason=None, failure_type="unspec"):

module_build_service/web/submit.py

@@ -701,6 +701,8 @@ def submit_module_build(db_session, username, stream_or_packager, params, module
                 reused_module_id=params.get("reuse_components_from"),
                 scratch=params.get("scratch"),
                 srpms=params.get("srpms"),
+                # don't commit now, we do it ourselves below
+                commit=False,
             )
             module.build_context, module.runtime_context, module.context, \
                 module.build_context_no_bms = module.contexts_from_mmd(module.modulemd)