Migrate Content Fields

Field Transformation Code Generation

Produces ready-to-use C# code files for the Migration.Tool.Extensions project. Takes the migration plan output from the migrate-content-plan skill — or a direct text description — as input.

Workflow

Step 1: Read Reference Materials

• Read references/field-migration-api.md for the complete API patterns and decision guides.
• If you need pattern examples for implementation, read assets/FIELD_MIGRATION_EXAMPLE.cs for a complete annotated reference implementation.
• If you need context on the migration tool's extension points or configuration, read ../_shared/references/migration-tool.md.
• If you need documentation links for the Kentico Migration Tool, read ../_shared/references/migration-docs.md.
• If a Kentico documentation lookup tool is available, use it for additional context on XbyK form components, data types, or the Migration Tool API.

Step 2: Analyze Input

• If a migration plan file path is provided → read it and extract from the Field Mappings section: Field Changes tables (scan for data type or form control changes), Custom Form Control Fields table (lists fields with non-built-in form controls and their handling mechanisms), and Custom Value Transforms table.
• If the migration plan has no Custom Form Control Fields section, scan the Field Changes tables for any field with a data type change or form control change column that is not handled by a built-in mapping or WithFieldPatch in an IClassMapping. These are candidates for IFieldMigration code or appsettings.json FieldMigrations config.
• If a direct text description is provided → identify source form controls, data types, field names, and transformation needs.
• Ask clarifying questions if the transformation logic, target form components, or scope (which classes) are ambiguous.

Step 3: Identify Migrations to Generate

Determine the set of IFieldMigration classes needed:

• One IFieldMigration class per logical transformation concern (e.g., one for custom rich text editors, one for HTML cleanup, one for date format conversion).
• Group related form controls or data types into a single migration when they share the same transformation logic.
• One ServiceCollectionExtensions class for DI registration.
• Cross-reference the built-in mapping table in ../_shared/references/migration-tool.md — the migration tool has default FieldMigration entries for standard data type + form control combinations (e.g., text + TextBoxControl → TextInput, longtext + HtmlAreaControl → RichTextEditor). It also has catch-all entries per data type (e.g., text + _other_ → TextInput, longtext + _other_ → TextArea). If a source form control matches a built-in entry or catch-all AND the target data type doesn't change, no IFieldMigration is needed.
• Check for data type changes: Built-in catch-all mappings preserve the source data type — they do not change it. If a field requires a data type change (e.g., text → longtext) AND a form control change, the catch-all won't produce the correct result. Use IFieldMigration code, appsettings.json FieldMigrations config, or IClassMapping.WithFieldPatch instead.
• Check the migration plan's Custom Form Control Fields section (if present) — fields marked with handling mechanism "IFieldMigration code" need code generation. Fields marked "Built-in catch-all", "FieldMigrations config", or "WithFieldPatch" do not.
• Skip code generation for:
  • Simple form control swaps with no value change → use appsettings.json FieldMigrations config instead.
  • Field renames or per-class value transforms → use IClassMapping SetFrom/ConvertFrom instead.
  • Field definition changes scoped to a single class → consider IClassMapping.WithFieldPatch instead.
  • Built-in conversions already handled by the migration tool defaults (including catch-all entries).
• Recommend IClassMapping.ConvertFrom when the transform is specific to one class and one field (per-class scope, not cross-class).
• Recommend IClassMapping.WithFieldPatch when the field definition change (data type, form component) is scoped to a single class and paired with an IClassMapping that already exists for that class.

Step 4: Generate Field Migration Code

For each migration, generate a class implementing IFieldMigration:

• Rank — use values < 100,000 (built-in defaults use 100,000+). Leave gaps between values (1000, 2000, 3000) for future insertions.
• ShallMigrate — precise matching on SourceFormControl, SourceDataType, FieldName, or ClassName. Avoid overly broad matches that interfere with built-in migrations.
• MigrateFieldDefinition — use System.Xml.Linq XElement API to patch XML field definitions (controlname, column type, data type, settings).
• MigrateValue — null-safe (null or DBNull check), type-safe (is string s pattern), context-aware (SourceObjectContext switch when behavior differs).
• Include a per-migration IServiceCollection extension method for DI registration.

Step 5: Generate Service Registration

Generate or update the ServiceCollectionExtensions static class:

• Call each migration's extension method.
• AddSingleton<IFieldMigration>(new T()) for each migration.
• Include comment noting that fields handled by IFieldMigration code do not need entries in appsettings.json FieldMigrations config.
• Include comment noting any prerequisite appsettings or IClassMapping registrations.

Step 6: Build Verification

1. Build the Migration.Tool.Extensions project to verify the generated code compiles without errors.
2. If the build fails, analyze the error messages, fix all issues in the generated code, and rebuild.
3. Repeat up to 3 attempts. If the build still fails after 3 attempts, present the full build output and error details to the user for manual resolution.

Step 7: Present and Refine

• Save files to the user-specified path (default: Migration.Tool.Extensions/FieldMigrations/ — generated code belongs in the Migration.Tool.Extensions project, matching the Migration.Tool.Extensions.FieldMigrations namespace).

• Provide a summary table of generated migrations:

  File	Pattern	Rank	Handles
  CommunityTextEditorFieldMigration.cs	Form control replacement	1000	CommunityTextEditor → RichTextEditor
  DateTextFieldMigration.cs	Data type conversion	2000	EventDateText text → datetime

• Ask if any migrations need adjustment and iterate on feedback.

Rules

• Namespace: Migration.Tool.Extensions.FieldMigrations (user can override).
• File naming: {DescriptiveName}FieldMigration.cs.
• Use string constants for source/target form control names and data types, following the Source_/Target_ prefix convention from the example.
• Add TODO comments for values unknown at generation time (e.g., target asset paths, lookup dictionaries).
• Follow exact API patterns from field-migration-api.md — do not invent methods that don't exist.
• Every IFieldMigration must have a corresponding AddSingleton<IFieldMigration>(new T()) registration.
• Handle both structured (migration plan) and free-text input.
• MigrateFieldDefinition uses System.Xml.Linq XElement API — find or create elements, set values, remove obsolete settings.
• MigrateValue must handle null (null or DBNull) and unexpected types defensively.
• Prefer IClassMapping.ConvertFrom for class-specific, per-field transforms; use IFieldMigration for cross-class or form-control-driven transforms.
• If a Kentico documentation lookup tool is available, verify uncertain API details before generating code.
• After generating code, always build the project and fix compilation errors before considering the task complete.

Gotchas

• ShallMigrate is called for every field in every class — must be lightweight and specific. Broad matching (e.g., all "text" fields) interferes with built-in migrations.
• MigrateFieldDefinition and MigrateValue must be aligned — if the definition changes the data type, the value must be converted to match.
• Custom rank values must be < 100,000 (built-in defaults use 100,000+; lower rank = higher priority).
• Fields handled by IFieldMigration do NOT need appsettings.json FieldMigrations entries. Skip code generation when config suffices (simple form control swap, no value transform).
• When a field definition change is scoped to a single class that already has an IClassMapping, prefer WithFieldPatch over IFieldMigration — it keeps the definition change co-located with the class mapping. Only use IFieldMigration when the same form control or data type change applies across multiple classes.
• Check SourceObjectContext when transformation behavior differs across pages, custom tables, and forms.
• This skill generates IFieldMigration code only — IClassMapping, ContentItemDirectorBase, IWidgetMigration, and IWidgetPropertyMigration are separate extension points.