Sqd Diag

SQLiteData Diagnostics

Symptom-based troubleshooting for SQLiteData issues.

1. Build/Compilation Errors

"Cannot find type 'Table' / '@Table'"

• Missing import SQLiteData (it re-exports StructuredQueriesSQLite)
• Package.swift missing swift-structured-queries dependency (should come transitively via SQLiteData)

"Cannot convert value of type 'X' to expected argument type..."

• Check that your @Table struct fields match the SQL schema types
• TEXT → String or UUID, INTEGER → Int or Bool, REAL → Double, BLOB → Data
• Enums must conform to QueryBindable

"Referencing static method 'buildExpression' requires..."

• Usually means a type mismatch in .select { } closure
• Check that @Selection struct field types match query expressions

Concurrency warnings on @Table structs

• Add nonisolated before the struct: @Table nonisolated struct Item { ... }

2. Runtime Database Errors

"no such table: X"

• Migration hasn't run → check migrator.migrate(database) is called
• Table name mismatch → @Table("customName") must match SQL CREATE TABLE "customName"
• In previews/tests: prepareDependencies not called

"no such column: X"

• Column name in Swift doesn't match SQL schema
• Migration adding the column hasn't been registered
• Swift property names are auto-converted to camelCase column names

"FOREIGN KEY constraint failed"

• Inserting child before parent exists
• Deleting parent without ON DELETE CASCADE
• SyncEngine handles this automatically during sync — if in app code, insert parent first

"NOT NULL constraint failed"

• Inserting NULL into a NOT NULL column without a default
• For CloudKit: use NOT NULL ON CONFLICT REPLACE DEFAULT <value>

"UNIQUE constraint failed"

• Duplicate primary key or unique column value
• For CloudKit-synced tables: unique constraints (except PK) are not allowed

"database is locked"

• Long-running read blocking writes (or vice versa)
• Consider using DatabasePool instead of DatabaseQueue
• Check for nested database.write calls

3. SyncEngine Errors

Quick symptom→fix map. For full CloudKit sync patterns, use /skill sqd-cloudkit.

4. @FetchAll / @FetchOne / @Fetch Issues

Data not updating in UI

• In @Observable class: add @ObservationIgnored to the fetch property wrappers
• Check database is the same instance: @Dependency(\.defaultDatabase) must be the prepared one
• prepareDependencies only called once?

"A blank, in-memory database is being used"

• prepareDependencies not called, or called after first access
• In previews: let _ = prepareDependencies { ... } at top of #Preview
• In tests: .dependency(\.defaultDatabase, ...) trait

Query returns empty but data exists

• Check query conditions: .where { } filter may be wrong
• Table name mismatch between SQL and @Table
• Database not migrated (tables don't exist)

Load error on @Fetch property

• Check $property.loadError for details
• Common: SQL syntax error in #sql(...) macro
• Common: Type mismatch between query output and expected type

@Fetch with FetchKeyRequest not loading

• FetchKeyRequest requires a key value before it fetches — check the key is set
• If using @Fetch(ItemRequest()) with a default key, ensure the key matches an actual row
• @Fetch does not auto-load on init — call load() or set a key to trigger the fetch
• Check $property.loadError — a nil key produces no error but also no data

ValueObservation / SharedReader stale data

• SharedReader caches the last emitted value — if the underlying query changes shape (e.g. table renamed), the reader stays stale
• @FetchAll uses ValueObservation internally — if the observed tables haven't changed, no update fires
• Writes via raw SQL (db.execute(sql:)) bypass StructuredQueries change tracking — use @Table query builders instead
• If using DatabaseQueue: only one connection, reads wait on writes — observation may appear delayed

"Cannot subscribe to observation" / subscription issues

• FetchSubscription.cancel() called too early
• Database connection closed
• Using DatabaseQueue in multithreaded context (use DatabasePool)

5. Migration Issues

eraseDatabaseOnSchemaChange causes data loss in dev

• This is expected behavior — it's a DEBUG-only convenience
• Wrap in #if DEBUG: migrator.eraseDatabaseOnSchemaChange = true
• For production: always add new migrations, never edit existing ones

migratePrimaryKeys throws

• Schema it doesn't know how to handle — fall back to manual migration
• See ManuallyMigratingPrimaryKeys docs

ALTER TABLE fails

• SQLite has limited ALTER TABLE support
• Can only: add columns, rename table, rename column
• Cannot: drop columns (SQLite 3.35+), add constraints to existing columns
• For complex changes: create new table, copy data, drop old, rename new

Migration ordering / dependencies

• Migrations run in registration order — if migration B references a table from migration A, register A first
• Never reorder existing migrations — new devices replay from the start
• If two migrations touch the same table, combine them or use explicit ordering keys
• CloudKit-synced schemas must be backwards-compatible — never remove or rename columns in migrations

6. Preview Issues

Previews crash or show empty data

#Preview {
  let _ = try! prepareDependencies {
    try $0.bootstrapDatabase()
    try? $0.defaultDatabase.seedSampleData()
  }
  ContentView()
}

CloudKit previews crash

• Mock cloud container is used automatically in preview context
• If still crashing: check SyncEngine init isn't hitting network
• Use startImmediately: false and don't call .start() in previews

7. Testing Issues

Tests interfere with each other

• Each test gets its own temporary database via defaultDatabase()
• Use .dependency(\.defaultDatabase, ...) trait per suite
• Don't share database instances across test suites

Test database has no tables

• Run migrations in test setup: try migrator.migrate(database)
• Or use bootstrapDatabase() helper

Preview works but tests fail (or vice versa)

• Preview and tests use different prepareDependencies calls — ensure both set up the same migrations
• Preview may use seedSampleData() which inserts rows — tests should start clean
• @MainActor isolation in tests can cause issues with database access — use nonisolated test methods or withDependencies for explicit setup

Device vs simulator differences

• Simulator uses different file paths — NSHomeDirectory() changes per boot
• CloudKit sync requires a real iCloud account — simulator with no account silently skips sync
• File protection levels behave differently in simulator — .completeUnlessOpen may not block reads as expected

Quick Diagnostic Checklist

1. import SQLiteData present?
2. prepareDependencies called once at app start?
3. migrator.migrate(database) called?
4. @ObservationIgnored on fetch property wrappers in @Observable?
5. Table names match between @Table and SQL?
6. Column types match between Swift and SQL?
7. For CloudKit: UUID primary keys with ON CONFLICT REPLACE?
8. For CloudKit: no UNIQUE constraints, no RESTRICT/NO ACTION?
9. Foreign key indexes created?
10. configuration.foreignKeysEnabled = true if using foreign keys?