feat(generator): add constructor-based mapping support#62
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…erialization - Introduced `DynamoMapperConstructorAttribute` to specify a constructor for DynamoDB deserialization. - Enables better control over deserialization in DynamoMapper.
- Added a new example project `DynamoMapper.MapperConstructor` to demonstrate constructor mapping. - Configured project dependencies for DynamoMapper runtime and generator. - Updated solution file to include the new example project.
- Added `RecordMapper` to map `PersonRecord` to and from DynamoDB items. - Added `ClassWithConstructor` to map `PersonClass` using a constructor for deserialization.
- Added tests for various class and record types with constructors or properties.
- Included scenarios like primary constructors, read-only properties, init-only properties,
and multiple constructors.
- Added failure cases for multiple attributed constructors.
- Ensures support for diverse constructor and property setups in DynamoMapper.
fix(diagnostics): add descriptor for multiple attributed constructors
- Introduced `DM0103` diagnostic descriptor for detecting multiple constructors marked with
`[DynamoMapperConstructor]`.
- Provides clear guidance to maintain a single attributed constructor per type.
…on methods - Added `ConstructorSelector` to determine suitable constructors for deserialization. - Introduced `InitializationMethod` to outline property initialization strategies during deserialization. - Implemented `PropertyInitializationMode` to support constructor and property-based mapping. - Enhanced property analysis with `MemberAnalyzer` for shared semantic logic. - Expanded `WellKnownTypeData` with `DynamoMapperConstructorAttribute`. This commit enables robust constructor-based deserialization in DynamoMapper.
…logic - Updated XML documentation to enhance clarity and consistency across multiple files. - Simplified conditional checks in `PropertyMappingCodeRenderer`. - Refactored `ConstructorSelector` with expanded multiline formatting for improved readability. - Applied minor naming adjustments and null checks where necessary. - Improved accessibility checks for property symbols in `AllPropertiesAccessible`. - Streamlined loop and conditional structures in `ModelClassInfo` and related files. This commit enhances code maintainability and improves readability without altering functionality.
… selection - Updated `AllPropertiesAccessible` to account for computed and read-only properties. - Improved constructor parameter matching for read-only properties during deserialization. - Refined logic to ignore computed properties that do not require construction population. - Expanded XML documentation for clear deserialization behavior guidelines. - Adjusted conditional logic to enhance clarity and deserialization accuracy.
…ML comments - Removed unused `<param>` XML comments in `PropertyMappingCodeRenderer` and `PropertyInfo`. - Corrected punctuation in diagnostic messages for consistency. - Added missing diagnostics to `AnalyzerReleases.Unshipped.md`.
- Added instructions for listing, filtering, and running tests for specific namespaces/classes. - Documented usage of xUnit v3 filtered test runs with Microsoft.Testing.Platform. - Included detailed examples for single test execution and method/class-level filters in `CLAUDE.md` and `AGENTS.md`.
…e initialization logic - Standardized punctuation for diagnostic `MessageFormat` across codebase and test snapshot files. - Adjusted comments in `ConstructorSelector` to clarify property initialization approach. - Enhanced initialization method logic to prefer object-initializer assignments for clarity and defaults.
…ection logic - Extracted property-related operations into dedicated methods for reusability and clarity. - Centralized constructor selection logic into a standalone method for improved maintainability. - Improved property analysis with modular functions for property initialization and diagnostics generation. - Enhanced readability and organization of `CreatePropertyInfos` and `CreateConstructorInfo`.
- Specified .NET SDK version as "10.0.101" for project consistency. - Added roll-forward policy set to "latestMinor" to allow minor version updates automatically.
ncipollina
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Jan 19, 2026
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I stopped my review after my comment. Let's discuss.
ncipollina
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🔥 Love this solution. One comment to address.
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❓ Why did you add this?
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This was needed to make MTP tests work when run through the CLI. I added this along with the agent commands so that coding agents could better run tests without burning tokens.
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This how you made it work with dotnet test?
Co-authored-by: Nick Cipollina <ncipollina@gmail.com>
…n in DynamoMapper - Added examples showcasing constructor-based deserialization in `index.md`. - Documented constructor selection rules for `FromItem` in `basic-mapping.md`. - Explained `[DynamoMapperConstructor]` usage in `attributes.md`. - Updated `how-it-works.md` with object construction approaches during deserialization. - Revised `phase-1.md` roadmap to include constructor-based deserialization support.
- Added detailed explanations for constructor mapping rules in `basic-mapping.md`. - Linked cross-references to constructor mapping rules from `attributes.md` and `how-it-works.md`. - Documented hybrid constructor and object initializer usage in `basic-mapping.md`. - Updated examples and added references for constructor-based deserialization scenarios.
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🚀 Pull Request
📋 Summary
This PR adds comprehensive support for constructor-based mapping in DynamoMapper, enabling the source generator to deserialize DynamoDB items into C# records and classes with parameterized constructors. This is a major enhancement that expands the types of domain models that can be used with DynamoMapper.
Key Features Added
Constructor-Based Deserialization: The generator now analyzes constructors and intelligently selects the best one for deserialization based on parameter-to-property matching.
[DynamoMapperConstructor]Attribute: Allows explicit constructor selection when multiple constructors are available.Primary Constructor Support: Full support for C# 12+ primary constructors on records and classes.
Init-Only Properties: Support for properties with
initaccessors that can only be set during object construction.Hybrid Initialization: Handles models that use both constructor parameters and settable properties, with smart property initialization mode detection.
Comprehensive Diagnostics: Added new compile-time diagnostics (DM0003-DM0007) to guide developers when constructor mapping issues are detected.
Changes by Component
Generator Enhancements:
ConstructorSelector: New component that analyzes and selects the best constructor for deserializationMemberAnalyzer: Shared logic for analyzing both properties and constructor parametersModelClassInfowith constructor metadata and initialization trackingFromItemmethodsRuntime API:
DynamoMapperConstructorAttributeto mark preferred constructorsTesting:
Documentation:
CLAUDE.mdandAGENTS.mdwith xUnit v3 test commandsDynamoMapper.MapperConstructorprojectTechnical Details
The constructor selection logic prioritizes:
[DynamoMapperConstructor]Property initialization modes are determined per-property:
ConstructorParameter: Property is set via constructor parameterDirectAssignment: Property is set after construction (regular orinitsetter)ReadOnly: Property is read-only and only set via constructor✅ Checklist
🧪 Related Issues or PRs
This PR implements a core Phase 1 feature for DynamoMapper, enabling it to work with a much broader range of domain models beyond simple POCOs with parameterless constructors.
💬 Notes for Reviewers
Areas to Focus On:
Constructor Selection Logic (
ConstructorSelector.cs): The algorithm for choosing the best constructor and matching parameters to properties. Pay attention to the name matching logic (exact, case-insensitive, underscore prefix handling).Property Initialization Modes: The logic in
ModelClassInfo.csthat determines whether each property should be set via constructor parameter or direct assignment.Template Changes (
Mapper.scriban): The newFromItemgeneration logic that handles constructor invocation with parameter mapping.Diagnostics: The new error messages (DM0003-DM0007) should be clear and actionable for developers.
Test Coverage: Review the snapshot tests in
ConstructorVerifyTests.csto ensure all edge cases are covered.Known Limitations:
Follow-up Work: