feat: add index for workflow_conversation_variables.conversation_id

This commit adds an index to the conversation_id column in the
workflow_conversation_variables table to improve query performance
when filtering by conversation ID. This is particularly important
for API endpoints that retrieve conversation variables for a specific
conversation.

The index is created via a new migration file and will help optimize
database queries as the application scales with more conversations
and variables.

Signed-off-by: -LAN- <laipz8200@outlook.com>

api/migrations/versions/2025_05_14_1403-d28f2004b072_add_index_for_workflow_conversation_.py

@@ -0,0 +1,33 @@
+"""add index for workflow_conversation_variables.conversation_id
+
+Revision ID: d28f2004b072
+Revises: 6a9f914f656c
+Create Date: 2025-05-14 14:03:36.713828
+
+"""
+from alembic import op
+import models as models
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision = 'd28f2004b072'
+down_revision = '6a9f914f656c'
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    # ### commands auto generated by Alembic - please adjust! ###
+    with op.batch_alter_table('workflow_conversation_variables', schema=None) as batch_op:
+        batch_op.create_index(batch_op.f('workflow_conversation_variables_conversation_id_idx'), ['conversation_id'], unique=False)
+
+    # ### end Alembic commands ###
+
+
+def downgrade():
+    # ### commands auto generated by Alembic - please adjust! ###
+    with op.batch_alter_table('workflow_conversation_variables', schema=None) as batch_op:
+        batch_op.drop_index(batch_op.f('workflow_conversation_variables_conversation_id_idx'))
+
+    # ### end Alembic commands ###

api/models/workflow.py

@@ -770,7 +770,7 @@ class ConversationVariable(Base):
     __tablename__ = "workflow_conversation_variables"
 
     id: Mapped[str] = mapped_column(StringUUID, primary_key=True)
-    conversation_id: Mapped[str] = mapped_column(StringUUID, nullable=False, primary_key=True)
+    conversation_id: Mapped[str] = mapped_column(StringUUID, nullable=False, primary_key=True, index=True)
     app_id: Mapped[str] = mapped_column(StringUUID, nullable=False, index=True)
     data = mapped_column(db.Text, nullable=False)
     created_at = mapped_column(db.DateTime, nullable=False, server_default=func.current_timestamp(), index=True)