chore(db): use a better way to export models and remove unused table (#11838)

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

api/models/workflow.py

@@ -12,12 +12,12 @@ import contexts
 from constants import HIDDEN_VALUE
 from core.helper import encrypter
 from core.variables import SecretVariable, Variable
-from extensions.ext_database import db
 from factories import variable_factory
 from libs import helper
 from models.enums import CreatedByRole
 
 from .account import Account
+from .engine import db
 from .types import StringUUID
 
 
@@ -399,7 +399,7 @@ class WorkflowRun(db.Model):
     graph = db.Column(db.Text)
     inputs = db.Column(db.Text)
     status = db.Column(db.String(255), nullable=False)  # running, succeeded, failed, stopped, partial-succeeded
-    outputs: Mapped[str] = mapped_column(sa.Text, default="{}")
+    outputs: Mapped[Optional[str]] = mapped_column(sa.Text, default="{}")
     error = db.Column(db.Text)
     elapsed_time = db.Column(db.Float, nullable=False, server_default=db.text("0"))
     total_tokens = db.Column(db.Integer, nullable=False, server_default=db.text("0"))