refactor: Replaces direct DB session usage with context managers (#20569)

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

api/core/workflow/graph_engine/graph_engine.py

 from core.workflow.nodes.enums import ErrorStrategy, FailBranchSourceHandle
 from core.workflow.nodes.event import RunCompletedEvent, RunRetrieverResourceEvent, RunStreamChunkEvent
 from core.workflow.nodes.node_mapping import NODE_TYPE_CLASSES_MAPPING
-from extensions.ext_database import db
 from models.enums import UserFrom
 from models.workflow import WorkflowType
 
                         error=str(e),
                     )
                 )
-            finally:
-                db.session.remove()
 
     def _run_node(
         self,
             agent_strategy=agent_strategy,
         )
 
-        db.session.close()
         max_retries = node_instance.node_data.retry_config.max_retries
         retry_interval = node_instance.node_data.retry_config.retry_interval_seconds
         retries = 0
             except Exception as e:
                 logger.exception(f"Node {node_instance.node_data.title} run failed")
                 raise e
-            finally:
-                db.session.close()
 
     def _append_variables_recursively(self, node_id: str, variable_key_list: list[str], variable_value: VariableValue):
         """

api/core/workflow/nodes/agent/agent_node.py

 from collections.abc import Generator, Mapping, Sequence
 from typing import Any, Optional, cast
 
+from sqlalchemy import select
+from sqlalchemy.orm import Session
+
 from core.agent.entities import AgentToolEntity
 from core.agent.plugin_entities import AgentStrategyParameter
 from core.memory.token_buffer_memory import TokenBufferMemory
             return None
         conversation_id = conversation_id_variable.value
 
-        # get conversation
-        conversation = (
-            db.session.query(Conversation)
-            .filter(Conversation.app_id == self.app_id, Conversation.id == conversation_id)
-            .first()
-        )
+        with Session(db.engine, expire_on_commit=False) as session:
+            stmt = select(Conversation).where(Conversation.app_id == self.app_id, Conversation.id == conversation_id)
+            conversation = session.scalar(stmt)
 
-        if not conversation:
-            return None
+            if not conversation:
+                return None
 
         memory = TokenBufferMemory(conversation=conversation, model_instance=model_instance)
 

api/core/workflow/nodes/knowledge_retrieval/knowledge_retrieval_node.py

 
 from sqlalchemy import Float, and_, func, or_, text
 from sqlalchemy import cast as sqlalchemy_cast
+from sqlalchemy.orm import Session
 
 from core.app.app_config.entities import DatasetRetrieveConfigEntity
 from core.app.entities.app_invoke_entities import ModelConfigWithCredentialsEntity
                 redis_client.zremrangebyscore(key, 0, current_time - 60000)
                 request_count = redis_client.zcard(key)
                 if request_count > knowledge_rate_limit.limit:
-                    # add ratelimit record
-                    rate_limit_log = RateLimitLog(
-                        tenant_id=self.tenant_id,
-                        subscription_plan=knowledge_rate_limit.subscription_plan,
-                        operation="knowledge",
-                    )
-                    db.session.add(rate_limit_log)
-                    db.session.commit()
+                    with Session(db.engine) as session:
+                        # add ratelimit record
+                        rate_limit_log = RateLimitLog(
+                            tenant_id=self.tenant_id,
+                            subscription_plan=knowledge_rate_limit.subscription_plan,
+                            operation="knowledge",
+                        )
+                        session.add(rate_limit_log)
+                        session.commit()
                     return NodeRunResult(
                         status=WorkflowNodeExecutionStatus.FAILED,
                         inputs=variables,

api/core/workflow/nodes/llm/node.py

 from typing import TYPE_CHECKING, Any, Optional, cast
 
 import json_repair
+from sqlalchemy import select, update
+from sqlalchemy.orm import Session
 
 from configs import dify_config
 from core.app.entities.app_invoke_entities import ModelConfigWithCredentialsEntity
         prompt_messages: Sequence[PromptMessage],
         stop: Optional[Sequence[str]] = None,
     ) -> Generator[NodeEvent, None, None]:
-        db.session.close()
-
         invoke_result = model_instance.invoke_llm(
             prompt_messages=list(prompt_messages),
             model_parameters=node_data_model.completion_params,
             return None
         conversation_id = conversation_id_variable.value
 
-        # get conversation
-        conversation = (
-            db.session.query(Conversation)
-            .filter(Conversation.app_id == self.app_id, Conversation.id == conversation_id)
-            .first()
-        )
-
-        if not conversation:
-            return None
+        with Session(db.engine, expire_on_commit=False) as session:
+            stmt = select(Conversation).where(Conversation.app_id == self.app_id, Conversation.id == conversation_id)
+            conversation = session.scalar(stmt)
+            if not conversation:
+                return None
 
         memory = TokenBufferMemory(conversation=conversation, model_instance=model_instance)
 
                 used_quota = 1
 
         if used_quota is not None and system_configuration.current_quota_type is not None:
-            db.session.query(Provider).filter(
-                Provider.tenant_id == tenant_id,
-                # TODO: Use provider name with prefix after the data migration.
-                Provider.provider_name == ModelProviderID(model_instance.provider).provider_name,
-                Provider.provider_type == ProviderType.SYSTEM.value,
-                Provider.quota_type == system_configuration.current_quota_type.value,
-                Provider.quota_limit > Provider.quota_used,
-            ).update(
-                {
-                    "quota_used": Provider.quota_used + used_quota,
-                    "last_used": datetime.now(tz=UTC).replace(tzinfo=None),
-                }
-            )
-            db.session.commit()
+            with Session(db.engine) as session:
+                stmt = (
+                    update(Provider)
+                    .where(
+                        Provider.tenant_id == tenant_id,
+                        # TODO: Use provider name with prefix after the data migration.
+                        Provider.provider_name == ModelProviderID(model_instance.provider).provider_name,
+                        Provider.provider_type == ProviderType.SYSTEM.value,
+                        Provider.quota_type == system_configuration.current_quota_type.value,
+                        Provider.quota_limit > Provider.quota_used,
+                    )
+                    .values(
+                        quota_used=Provider.quota_used + used_quota,
+                        last_used=datetime.now(tz=UTC).replace(tzinfo=None),
+                    )
+                )
+                session.execute(stmt)
+                session.commit()
 
     @classmethod
     def _extract_variable_selector_to_variable_mapping(

api/core/workflow/nodes/parameter_extractor/parameter_extractor_node.py

 from core.workflow.nodes.enums import NodeType
 from core.workflow.nodes.llm import LLMNode, ModelConfig
 from core.workflow.utils import variable_template_parser
-from extensions.ext_database import db
 
 from .entities import ParameterExtractorNodeData
 from .exc import (
         tools: list[PromptMessageTool],
         stop: list[str],
     ) -> tuple[str, LLMUsage, Optional[AssistantPromptMessage.ToolCall]]:
-        db.session.close()
-
         invoke_result = model_instance.invoke_llm(
             prompt_messages=prompt_messages,
             model_parameters=node_data_model.completion_params,