[bugfix]: AI conversation message loading issue

[P-Peaceful]

What's changed?

fixed: #3868

In HertzBeat AI feature, when users switch between multiple conversations, the chat history disappears and only the default welcome page is displayed. This is caused by JPA's @OneToMany lazy loading mechanism that prevents proper data loading.

Root Cause Analysis

The core issue lies in JPA's @OneToMany lazy loading behavior:

1. Lazy Loading Mechanism: The messages field in ChatConversation entity uses @OneToMany annotation with default lazy loading (FetchType.LAZY) strategy
2. Session Closure Issue: When fetching conversation objects via conversationDao.getReferenceById() or findById(), accessing the messages collection after Hibernate Session closure triggers LazyInitializationException or returns empty collections
3. Proxy Object Trap: getReferenceById() returns a proxy object without immediately triggering database queries, causing associated message data to remain unloaded
4. Transaction Boundary: After Service layer methods return, transactions are committed and Hibernate Sessions are closed, preventing lazy-loaded associations from being loaded

Solution

Adopt explicit query strategy instead of relying on JPA's automatic association loading:

1. Add Dedicated Query Methods: Add findByConversationIdOrderByGmtCreateAsc() and findByConversationIdInOrderByGmtCreateAsc() methods in ChatMessageDao for explicit message queries
2. Manual Message Loading: Explicitly query and set messages to conversation objects where message data is needed
3. Batch Loading Optimization: In getAllConversations() method, use IN query to load all conversation messages at once, avoiding N+1 query problem
4. Transaction Management: Add @Transactional annotation to deleteConversation() method to ensure atomicity of delete operations

Testing

20251214-212937.mp4

Checklist

• I have read the Contributing Guide
• I have written the necessary doc or comment.
• I have added the necessary unit tests and all cases have passed.

Add or update API

• I have added the necessary e2e tests and all cases have passed.

[tomsun28]

lgtm!