Refactor models for better readability

**Problem**
When working with data, the error messages could be more descriptive.

**Suggestion**
Improve error handling and add detailed error messages.

**Context**
This would help with debugging and maintenance.

The issue names no files, tests, or model entry points, so first locate the models and error-handling paths involved in data operations. Clarify which failures need more detail and define tests that demonstrate the improved messages before changing the implementation.

Written by the indexing model from the issue text.