Allow partial update for creating embeddings based on @Vectorize annotation

[raphaeldelio]

[bsbodden]

@raphaeldelio can you add some detail? Thx!

Does this 👇 match?

Issue #597: Allow partial update for creating embeddings based on @vectorize annotation

Problem:
Currently, when saving an entity with @vectorize annotated fields, the embedder always regenerates the embedding regardless of whether the source field has actually changed. This is problematic
because:

1. Cost: Embedding generation via external APIs (OpenAI, Azure, etc.) incurs API costs
2. Latency: Embedding generation adds latency to save operations
3. Unnecessary work: If you're updating a non-vectorized field (e.g., price), you shouldn't need to regenerate the embedding for description

Current Behavior:
In DefaultEmbedder.processEntity():

  if (fieldValue != null) {
      // Always generates embedding if source field has a value
      processSentenceEmbedding(accessor, vectorize, fieldValue, isDocument);
  }

Proposed Solution:

The fix requires tracking whether the source field has changed. Options include:

1. Compare with existing embedding source: Before generating, check if the current source value differs from what was used to generate the existing embedding (requires storing the source hash or
   value)
2. Add @vectorize option for conditional generation: Add an option like onlyIfChanged = true that skips regeneration if the destination field already has a value
3. Dirty field tracking: Track which fields have been modified and only regenerate embeddings for changed source fields
4. Explicit partial update API: Provide a separate method like updateWithoutVectorization() or add options to save() to skip embedding generation

Simplest Implementation (Option 2):

Add a skipIfPopulated attribute to @vectorize:

  @Vectorize(destination = "descriptionEmbedding", skipIfPopulated = true)
  private String description;

  Then in DefaultEmbedder.processEntity():
  if (fieldValue != null) {
      Object existingEmbedding = accessor.getPropertyValue(vectorize.destination());
      if (!vectorize.skipIfPopulated() || existingEmbedding == null) {
          // Generate embedding
      }
  }

This allows users to opt-in to skip regeneration when the embedding already exists.