DomainMapper 1.2.0

DomainMapper

Map data. Preserve invariants.

DomainMapper is a small compile-time mapper for .NET with a domain-driven design bias. Its source generator emits direct C# and does not use runtime reflection. Version 1.2.0 adds opt-in collection policies, reference preservation, runtime dispatch, and query projections while retaining domain-owned constructors and factories.

Version 1.2.0

Install DomainMapper from NuGet with:

dotnet add package DomainMapper --version 1.2.0

Domain-first mapping

using DomainMapper.Abstractions;

[DomainMapper]
public static partial class OrderMapper
{
    [DomainFactory(Input = DomainFactoryInput.Source)]
    private static OrderId ToOrderId(int value) => new(value);

    [MapToFactory(nameof(Order.Place))]
    public static partial Order Place(OrderDraft source);
}

[MapToFactory] makes the target-owned factory mandatory. DomainMapper binds source properties and additional mapping parameters to factory parameters by name and applies mapper-owned [DomainFactory] conversions where their source and target types match. Explicit mapping parameters take precedence over same-named root source properties. If the target cannot be constructed completely, generation fails instead of bypassing the domain boundary or silently dropping state.

Supported mappings

DomainMapper 1.2.0 supports:

• mutable targets with accessible parameterless constructors;
• immutable targets and records with accessible constructors;
• target-owned static factories through [MapToFactory];
• mapper-owned source-value and member-bound conversions through [DomainFactory];
• nested objects, arrays, lists, read-only collection targets, and mutable or read-only dictionary interfaces;
• existing-target property updates;
• explicit property and field renames, including nested source paths;
• typed computed target members and additional mapping parameters;
• target/source completeness, typed ignores, and allow-listed partial updates;
• conditional and null-aware assignments with constant substitution;
• typed completion hooks, mapping composition, and bounded recursion;
• Replace, ClearAndFill, and Append policies for existing-target collections;
• invocation-local reference preservation for mutable cyclic graphs;
• closed-world generated runtime dispatch with explicit derived-source opt-in;
• cached provider-neutral expression projections through the separate DomainMapper.Projections contract package;
• nested and generic mapper types and generic mapping methods;
• direct generated code that enumerates general sequences and preallocates only when the source exposes a count.

Fields participate when they are named by an explicit mapping contract; convention mapping remains property-only for compatibility. See the authoritative capabilities and limitations and versioned changelog.

Construction is fail-closed: every accessible writable target member must be mapped, and source-matched target state that is not writable from the generated mapper is rejected with DMPR101.

Unsupported projection or tracking shapes fail at build time. Private-member mutation remains unsupported, and no feature scans assemblies, infers persistence semantics, or introduces mutable runtime mapping configuration.

Build and test

dotnet restore DomainMapper.slnx -p:HUSKY=0
dotnet build DomainMapper.slnx --configuration Release --no-restore -p:HUSKY=0
dotnet test test/DomainMapper.Tests/DomainMapper.Tests.csproj --configuration Release --no-build -p:HUSKY=0

Run the sample with:

dotnet run --project samples/DomainMapper.Sample/DomainMapper.Sample.csproj

Benchmarks

The comparison suite pins Mapperly 4.3.1 and measures both generated runtime mappings and cold source generation in balanced execution orders.

DOMAINMAPPER_BENCHMARK_PAIRS=6 ./scripts/run-stable-benchmarks.sh

See the benchmark methodology.

Project layout

• src/DomainMapper.Abstractions — public, compile-time mapping attributes and policy types.
• src/DomainMapper.Projections — optional provider-neutral projection declaration contract.
• src/DomainMapper/Engine — contract discovery, semantic planning, conversion policy, and C# emission.
• test/DomainMapper.Tests — engine contract and performance-gate tests.
• benchmarks/DomainMapper.Benchmarks — balanced DomainMapper-versus-Mapperly evidence.
• samples/DomainMapper.Sample — aggregate construction through a domain factory.

License

DomainMapper is licensed under Apache-2.0. Third-party attribution is retained in NOTICE.