高效识别待删除子实体：无需额外DB查询的方案探讨

Nice question! Let's break down your current approaches and dive into some more robust, general-purpose solutions for managing child entity updates without needing to fetch existing data from the database first.

First, Let's Evaluate Your Two Existing Options #

Option 1: Separate Deletion ID List #

Your first approach sends a dedicated actorsToBeDeleted array alongside the updated parent entity and child list.

public class MovieUpdateRequest { 
    Movie movie; 
    int[] actorsToBeDeleted; 
}

• Pros: Clean separation of concerns—your child entity model stays untouched, and the deletion logic is explicit. Backend code can directly process the ID list to mark records as deleted.
• Cons: Frontend has extra work to track deleted IDs (e.g., handling undo-delete actions can get messy). It also doesn't handle "unchanged" child entities explicitly, though that might not be an issue for your use case.

Option 2: Non-Mapped Deletion Flag on Child Entity #

Adding a toBeDeleted flag to the Actor class (marked as not mapped to the database) lets frontend mark which children need deletion.

public class Actor { 
    int id; 
    String name; 
    @NotMapped Boolean toBeDeleted; 
}

• Pros: Intuitive for frontend—each child entity carries its own deletion state, so it's easy to tie to UI actions (like a delete button per actor).
• Cons: Pollutes your core Actor entity with UI/request-specific logic. If you reuse this entity elsewhere (e.g., for read operations), the unused flag can cause confusion or unintended side effects.

Better, More General-Purpose Solutions #

1. Use a DTO with a Status Enum (Recommended for Most Cases) #

Instead of modifying your core entity, create a Data Transfer Object (DTO) for the child entity that includes a status enum covering all possible states. This keeps your domain model clean while giving you full control over each child's intended action.

public enum EntityActionStatus {
    NEW,       // ID = 0, needs to be created
    MODIFIED,  // ID exists, needs updates
    DELETED,   // ID exists, needs to be marked as deleted
    UNCHANGED  // No action needed (can be omitted if you don't send unchanged entities)
}

public class ActorDto {
    int id;
    String name;
    EntityActionStatus status;
}

public class MovieUpdateRequest {
    Movie movie;
    List<ActorDto> actors;
}

• Why this works: Frontend sets the status for each actor (e.g., NEW when adding a new actor, DELETED when checking a delete box), and your backend can process each child in one pass:
  • For NEW: Insert the actor
  • For MODIFIED: Update the existing actor
  • For DELETED: Mark the actor as deleted (or hard delete, depending on your needs)
  • For UNCHANGED: Skip entirely
• Pros: Covers all CRUD cases in a single structure, keeps domain entities pure, and reduces ambiguity compared to a single deletion flag.

2. Delta Patch Request (Optimal for Large Datasets) #

If you're dealing with a lot of child entities and want to minimize data transfer, split your update request into three distinct lists for each action:

public class MovieUpdateRequest {
    Movie movie;
    List<Actor> newActors;       // Actors to add (ID = 0)
    List<Actor> updatedActors;   // Actors to modify (ID exists, with changes)
    int[] deletedActorIds;       // IDs of actors to delete
}

• Why this works: Frontend only sends the data that actually changed. Your backend doesn't have to filter through unchanged entities—just process each list directly.
• Pros: Maximum efficiency (smaller payload size), crystal-clear logic for both frontend and backend, and no need to parse status flags. Great for scenarios where child entities are numerous or large.

Final Recommendations #

• If you want a simple, low-effort solution that works for small to medium datasets: Stick with Option 2, but use a DTO instead of adding the flag to your core Actor entity to avoid model pollution.
• If you need a scalable, clean solution that covers all edge cases: Go with the Status Enum DTO approach—it's the most flexible and widely adopted pattern for this kind of nested CRUD.
• If performance or payload size is a top priority: Use the Delta Patch Request structure to minimize data transfer and processing overhead.

内容的提问来源于stack exchange，提问作者John Steed