Make URN mandatory for UK schools and NCES ID mandatory for US schools

[Mohamed-RPF]

Make URN mandatory for UK schools and NCES ID mandatory for US schools

Add conditional presence validation for UK URN (reference) and US NCES ID (district_nces_id) fields, with format validation and scoped uniqueness to allow reuse after school rejection. This improves validation error handling so users receive specific, actionable error messages instead of generic form errors.

Status

Closes: https://github.com/orgs/RaspberryPiFoundation/projects/51/views/11?pane=issue&itemId=120513360&issue=RaspberryPiFoundation%7Cdigital-editor-issues%7C780

Related to: (standalone url)

Points for consideration:

Security

• Partial unique indexes prevent duplicate entries among active (non-rejected) schools
• Format validation enforces strict digit patterns (5-6 digits for URN, 12 digits for NCES ID)
• Case-insensitive uniqueness check prevents bypass attempts

What's changed?

Database:

• Converted reference index to partial unique index (WHERE rejected_at IS NULL)
• Converted district_nces_id index to partial unique index (WHERE rejected_at IS NULL)
• This allows rejected schools to release their identifiers for reuse by legitimate schools

Model (School):

• Added conditional presence validation: reference required for UK (country_code == 'GB')
• Added conditional presence validation: district_nces_id required for US (country_code == 'US')
• Added format validation: URN must be 5-6 digits, NCES ID must be 12 digits
• Added scoped uniqueness: only active (non-rejected) schools are checked for duplicates
• Added united_kingdom? and united_states? helper methods

API Error Responses:

Field	Validation	Error Message
reference	presence	"can't be blank"
reference	uniqueness	"has already been taken"
reference	format	"must be 5-6 digits (e.g., 100000)"
district_nces_id	presence	"can't be blank"
district_nces_id	uniqueness	"has already been taken"
district_nces_id	format	"must be 12 digits (e.g., 010000000001)"

Tests:

• 16 comprehensive validation tests covering:
  • Conditional presence (UK/US specific)
  • Format validation (valid/invalid patterns)
  • Scoped uniqueness (allows reuse after rejection)
• Updated factory to include valid reference for default GB schools