Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx skills add ComeOnOliver/skillshub --skill axiom-swiftdata-migrationgit clone --depth 1 https://github.com/ComeOnOliver/skillshubWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/comeonoliver/skillshub/axiom-swiftdata-migration)<a href="https://agentmods.dev/skills/comeonoliver/skillshub/axiom-swiftdata-migration"><img src="https://agentmods.dev/badge/skills/comeonoliver/skillshub/axiom-swiftdata-migration/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/comeonoliver/skillshub/axiom-swiftdata-migration"><img src="https://agentmods.dev/badge/skills/comeonoliver/skillshub/axiom-swiftdata-migration.svg" alt="Reviewed on agentmods" width="80" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00061 | $0.06383 |
| Opus 5 | $0.00030 | $0.03191 |
| Sonnet 5 | $0.00012 | $0.01277 |
| Haiku 4.5 | $0.00006 | $0.00638 |
Grade A, and why
axiom-swiftdata-migration scanned grade A with 1 finding against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 7d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Makes network callslowCapability
Not a fault in itself. Listed so you know the mod talks to something, and to what.
let v1Notes = try context.fetch(FetchDescriptor<SchemaV1.Note>()) How it starts
The opening of the file, as written. The whole thing — 963 lines — stays where its author put it; the contents beside it link to each section on GitHub.
SwiftData Custom Schema Migrations
Overview
SwiftData schema migrations move your data safely when models change. Core principle SwiftData's willMigrate sees only OLD models, didMigrate sees only NEW models—you can never access both simultaneously. This limitation shapes all migration strategies.
Requires iOS 17+, Swift 5.9+
Target iOS 26+ (features like propertiesToFetch)
When Custom Migrations Are Required
Lightweight Migrations (Automatic)
SwiftData can migrate automatically for:
- ✅ Adding new optional properties
- ✅ Adding new required properties with default values
- ✅ Removing properties
- ✅ Renaming properties (with
@Attribute(originalName:)) - ✅ Changing relationship delete rules
- ✅ Adding new models
Custom Migrations (This Skill)
You need custom migrations for:
- ❌ Changing property types (
String→AttributedString,Int→String) - ❌ Making optional properties required (must populate existing nulls)
- ❌ Complex relationship restructuring
- ❌ Data transformations (splitting/merging fields)
- ❌ Deduplication when adding unique constraints
Example Prompts
These are real questions developers ask that this skill is designed to answer:
1. "I need to change a property from String to AttributedString. How do I migrate existing data with relationships intact?"
→ The skill shows the two-stage migration pattern that works around the willMigrate/didMigrate limitation
2. "My model has a one-to-many relationship with cascade delete. How do I preserve this during a type change migration?"
→ The skill explains relationship prefetching and maintaining inverse relationships across schema versions
3. "I have a many-to-many relationship between Tags and Notes. The migration is failing with 'Expected only Arrays for Relationships'. What's wrong?"
→ The skill covers explicit inverse relationship requirements and iOS 17.0 alphabetical naming bug
4. "I need to rename a model but keep all its relationships intact."
→ The skill shows @Attribute(originalName:) patterns for lightweight migration
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 7d ago First seen · 963 lines · 61 tokens per session scan A d9761db57e3f
axiom-swiftdata-migration is a skill published in the GitHub repository ComeOnOliver/skillshub (63 stars, last pushed 2mo ago), licensed MIT. It adds 61 tokens to every session and 6,383 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 1 finding (makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-03.
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