Refactor: replace count() > 0 check with exists() (#24583)

Co-authored-by: Yongtao Huang <99629139+hyongtao-db@users.noreply.github.com>
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>

api/models/model.py

@@ -17,7 +17,7 @@ if TYPE_CHECKING:
 import sqlalchemy as sa
 from flask import request
 from flask_login import UserMixin
-from sqlalchemy import Float, Index, PrimaryKeyConstraint, String, func, text
+from sqlalchemy import Float, Index, PrimaryKeyConstraint, String, exists, func, select, text
 from sqlalchemy.orm import Mapped, Session, mapped_column
 
 from configs import dify_config
@@ -1553,7 +1553,7 @@ class ApiToken(Base):
     def generate_api_key(prefix, n):
         while True:
             result = prefix + generate_string(n)
-            if db.session.query(ApiToken).where(ApiToken.token == result).count() > 0:
+            if db.session.scalar(select(exists().where(ApiToken.token == result))):
                 continue
             return result