Fix very slow workflow editor loading

Loading the editor for my usegalaxy.org account takes 20 seconds. I've
narrowed this down to the unnecessary join against the workflow table
and loading all steps. I'm also returning the needed columns directly.

lib/galaxy/webapps/galaxy/controllers/workflow.py

@@ -1,8 +1,13 @@
 import logging
 
 from markupsafe import escape
-from sqlalchemy import desc
-from sqlalchemy.orm import joinedload
+from sqlalchemy import (
+    and_,
+    desc,
+    false,
+    func,
+    select,
+)
 
 from galaxy import (
     model,
@@ -166,13 +171,32 @@ def editor(self, trans, id=None, workflow_id=None, version=None, **kwargs):
 
         # The following query loads all user-owned workflows,
         # So that they can be copied or inserted in the workflow editor.
-        workflows = (
-            trans.sa_session.query(model.StoredWorkflow)
-            .filter_by(user=trans.user, deleted=False, hidden=False)
-            .order_by(desc(model.StoredWorkflow.table.c.update_time))
-            .options(joinedload(model.StoredWorkflow.latest_workflow).joinedload(model.Workflow.steps))
-            .all()
+        assert trans.user  # help out type checker, require_login means we will have a user
+        workflow_stmnt = (
+            select(
+                model.StoredWorkflow.id,
+                model.StoredWorkflow.latest_workflow_id,
+                model.StoredWorkflow.name,
+                func.coalesce(func.count(model.WorkflowStep.id), 0).label("step_count"),
+            )
+            .join(
+                model.WorkflowStep,
+                model.StoredWorkflow.latest_workflow_id == model.WorkflowStep.workflow_id,
+                isouter=True,
+            )
+            .where(
+                and_(
+                    model.StoredWorkflow.user_id == trans.user.id,
+                    model.StoredWorkflow.deleted == false(),
+                    model.StoredWorkflow.hidden == false(),
+                )
+            )
+            .group_by(
+                model.StoredWorkflow.id,
+            )
+            .order_by(desc(model.StoredWorkflow.update_time))
         )
+        workflow_results = trans.sa_session.execute(workflow_stmnt).all()
 
         # create workflow module models
         module_sections = []
@@ -219,13 +243,13 @@ def editor(self, trans, id=None, workflow_id=None, version=None, **kwargs):
         # create workflow models
         workflows = [
             {
-                "id": trans.security.encode_id(workflow.id),
-                "latest_id": trans.security.encode_id(workflow.latest_workflow.id),
-                "step_count": len(workflow.latest_workflow.steps),
-                "name": workflow.name,
+                "id": trans.security.encode_id(stored_workflow_id),
+                "latest_id": trans.security.encode_id(latest_workflow_id),
+                "step_count": step_count,
+                "name": workflow_name,
             }
-            for workflow in workflows
-            if new_workflow or workflow.id != stored.id
+            for stored_workflow_id, latest_workflow_id, workflow_name, step_count in workflow_results
+            if not stored or stored_workflow_id != stored.id
         ]
 
         # build workflow editor model
@@ -236,7 +260,7 @@ def editor(self, trans, id=None, workflow_id=None, version=None, **kwargs):
         }
 
         # for existing workflow add its data to the model
-        if new_workflow is False:
+        if stored:
             editor_config.update(
                 {
                     "id": trans.security.encode_id(stored.id),