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Convention-based object-to-object compile time mapper for .NET

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dotMap for .NET

Convention-based object-to-object compile time mapper for .NET.

It simplifies the process of transferring data between objects, reducing the need for manual mapping code. dotMap leverages a set of conventions to map properties between source and destination types, minimizing configuration while maintaining flexibility. This library is particularly useful in scenarios where objects have similar structures, such as in data transfer objects (DTOs) and domain models, enabling developers to focus more on business logic rather than boilerplate mapping code.

dotMap is ideal for developers looking for a streamlined and reliable solution for object mapping in .NET applications, improving code maintainability and reducing the likelihood of errors during data transfer operations.

Table of contents

Key features

  • Convention-Based Mapping: Automatically maps properties with matching names between source and destination objects.
  • Compile-Time Checking: Ensures mappings are verified at compile time, reducing runtime errors.
  • Nested Mappings: Supports deep object graphs, allowing complex objects to be mapped effortlessly.
  • Configurable: Easily configurable to support value transformations, and meet object construction requirements.

Installation

  • Install NuGet, if not installed yet.
  • Add dotMap from the package manager console.
PM> Install-Package dotMap
  • Alternatively, add dotMap from the .NET CLI.
dotnet add package dotMap

Usage example

  • Define map configuration
  • Get instance of the class by calling automatically generated extension method that is unique for your object
using FluentAssertions;
using Xunit;

public class Example
{
  [Fact]
  public void Test()
  {
    var source = new Source { Name = "Foo" };
    var destination = source.MapToDestination();
    // destination.Name has the same value as source.Name
    destination.Name.Should().Be(source.Name);
  }
  
  private class Configuration : IMapConfig
  {
    public void ConfigureMap(MapConfig config)
    {
      config
        .Map<Source>()
        .To<Destination>();
    }
  }
}

internal class Destination
{
  public string Name { get; set; }
}

public class Source
{
  public string Name { get; set; }
}

👉 Check more examples right in the source code.

How does it work?

Once the map configuration is defined, dotMap generates new files with classes that provide extension methods for the source object that allow you to get an instance of the target object while preserving the source values based on the defined configuration.

classDiagram
  class Source {
    +string name
    +getName()
  }
  class Destination {
    +string Name
    +string GetName
  }
  class Configuration {
    +ConfigureMap(MapConfig config)
  }
  class IMapConfig {
    <<Interface>>
    +ConfigureMap(MapConfig config)
  }
  class ConfigurationExtensions {
    <<Autogenerated>>
    Destination MapToDestination(this Source source)
    IEnumerable<Destination> MapToDestination(this IEnumerable<Source> source)
  }
  note for ConfigurationExtensions "var source = new Source { name = &quot;Foo&quot; };
  // Get mapped object by calling extension method
  var destination = source.MapToDestination();
  asd"
  Configuration<|--IMapConfig
  ConfigurationExtensions-->Configuration
  ConfigurationExtensions..>Source
  ConfigurationExtensions..>Destination
Loading

Here is the code that is generated for the previous example.

namespace dotMap.Tests.Examples
{
  public static class Tests_ConfigurationExtensions
  {
    internal static dotMap.Tests.Examples.Destination MapToDestination(this dotMap.Tests.Examples.Source source)
    {
      var result = new dotMap.Tests.Examples.Destination()
      {
        Name = source.Name
      };
      return result;
    }

    internal static IEnumerable<dotMap.Tests.Examples.Destination> MapToDestination(this IEnumerable<dotMap.Tests.Examples.Source> source)
    {
      return source?.Select(item => item == null ? null : Tests_ConfigurationExtensions.MapToDestination(item));
    }
  }
}

Tutorials

Configuration variations

Declarative configuration

There are several mechanisms for defining a map configuration. One is to define a configuration in a separate class by implementing the ConfigureMap method, as follows.

private class Configuration : IMapConfig
{
  public void ConfigureMap(MapConfig config)
  {
    config
      .Map<Source>()
      .To<Destination>()
      .WithDestinationNamingConvention<PascalCaseConvention>();
  }
}

An alternative solution is to define the configuration directly in the object definition.

internal class Destination : IMappable<Destination>
{
  public string Name { get; set; }
  
  public void ConfigureMap(MapConfig<Destination> map)
  {
    map
      .From<Source>()
      .WithDestinationNamingConvention<PascalCaseConvention>();
  }
}

Imperative configuration

The other way to define map configuration is to use attributes.

[MapFrom(typeof(Source), DestinationMembersNamingConvention = typeof(PascalCaseConvention))]
internal class Destination
{
  public string? Name { get; set; }

  [Ignore]
  public int Year { get; set; }
}

public class Source
{
  public string? name { get; set; }
  public int year { get; set; }
}

Multiple configurations

It is allowed to have multiple configurations.

Also, a single source object can be mapped to multiple destination objects.

private class Configuration : IMapConfig
{
  public void ConfigureMap(MapConfig config)
  {
    config
      .Map<Source>()
      .To<Destination>();
    config
      .Map<Source>()
      .To<Destination2>()
      .Ignore(m => m.Year);
  }
}

Here is another example where attributes are used for the same purpose.

[MapFrom(typeof(Source))]
[MapFrom(typeof(Source2))]
internal class Destination
{
  public string? Name { get; set; }
  // Ignore for all mappings
  [Ignore]
  public int Year { get; set;  }
  // Ignore for `Source2` mapping only
  [Ignore(For = typeof(Source2))]
  public decimal Cost { get; set; }
}

Use of naming conversion

If member names of the source and destination objects match, the map configuration can be as simple as following.

private class Configuration : IMapConfig
{
  public void ConfigureMap(MapConfig config)
  {
    config
      .Map<Source>()
      .To<Destination>();
  }
}

However, if the source object uses a different naming convention than the destination object, we need to specify the naming conversion rules to match object members between the objects.

private class Configuration : IMapConfig
{
  public void ConfigureMap(MapConfig config)
  {
    config
      .Map<Source>()
      .To<Destination>()
      .WithDestinationNamingConvention<PascalCaseConvention>();
  }
}

internal class Destination
{
  public string? Name { get; set; }
}

public class Source
{
  public string? name { get; set; }
}

Another example is constructor parameters, which may differ between source and destination objects, so the naming conversion rule should be specified to match constructor parameters.

[MapFrom(typeof(source),
  DestMappingMode = DestMappingMode.MapToConstructor,
  DestinationConstructorNamingConvention = typeof(CamelCaseConvention))]
internal class Destination
{
  public Destination(string firstName)
  {
    FirstName = firstName;
  }

  public string FirstName { get; }
}

public class source
{
  public string first_name { get; set; }
}

List of supported naming conversions

As long as source and destination objects use the same naming convention, it can be any. However, if object member names need to be converted to a different naming convention to match, the naming conversion should be used.

The following naming conversions are built in and supported:

  • CamelCase
  • pascalCase
  • snake_case

Choose members to map and ignore

Mapping mode

You can choose which object members to map, such as properties, fields, and methods. By default, properties and fields are mapped.

This behavior can be configured by specifying one of the MappingMode:

  • MapPropsAndFields to map properties and fields only
  • MapMethods to map methods only
  • MapAllMembers to map properties, fields, and methods
public void ConfigureMap(MapConfig config)
{
  config
    .Map<Source>()
    .To<Destination>()
    .WithMappingMode(SourceMappingMode.MapAllMembers);
}

Consider the following example where SourceMappingMode is set to map methods only. Since Source.GetCost() is a method, and thus can be mapped, and has a matching member name of which is a property of Destination.GetCost.

private class Configuration : IMapConfig
{
  public void ConfigureMap(MapConfig config)
  {
    config
      .Map<Source>()
      .To<Destination>()
      // Source.GetCost() gets mapped to Destination.GetCost
      .WithMappingMode(SourceMappingMode.MapMethods);
  }
}

internal class Destination
{
  public int GetCost { get; set; }
}

public class Source
{
  public int GetCost() => 100;
}

Ignore member

If a particular member is not needed, it can be excluded from the map configuration so that its value is not copied.

using FluentAssertions;
using Xunit;

private class Configuration : IMapConfig
{
  public void ConfigureMap(MapConfig config)
  {
    config
      .Map<Source>()
      // Name property gets value copied
      .To<Destination>()
      // Year property is ignored and will equal default value of 0
      .Ignore(m => m.Year);
  }
}

internal class Destination
{
  public string? Name { get; set; }
  public int Year { get; set;  }
}

public class Source
{
  public string? Name { get; set; }
  public int Year { get; set; }
}

Use of constructor

If the object construction needs to pass an argument, use ConstructFrom.

This could also be used to adjust the value of the member. However, depending on the design requirements of an object, there are other approaches available. Read more in the Customize member value tutorial.

using FluentAssertions;
using Xunit;

public class Example
{
  [Fact]
  public void Test()
  {
    var source = new Source { Name = "Foo", Year = 2024 };
    var destination = source.MapToDestination();
    destination.Name.Should().Be("Foo 2024");
  }

  private class Configuration : IMapConfig
  {
    public void ConfigureMap(MapConfig config)
    {
      config
        .Map<Source>()
        .To<Destination>()
        .ConstructFrom(source => new Destination($"{source.Name} {source.Year}"))
        .Ignore(m => m.Name);
    }
  }
}

internal class Destination(string name)
{
  public string Name { get; init; } = name;
}

public class Source
{
  public string Name { get; set; }
  public int Year { get; set; }
}

Customize member value

Object customization

Pass an action to the Finally method call to execute the logic required to adjust destination object.

using FluentAssertions;
using Xunit;

public class Example
{
  [Fact]
  public void Test()
  {
    var source = new Source { Name = "Foo", Year = 2024 };
    var destination = source.MapToDestination();
    destination.Name.Should().Be("Foo 2024");
  }

  private class Configuration : IMapConfig
  {
    public void ConfigureMap(MapConfig config)
    {
      config
      .Map<Source>()
      .To<Destination>()
      .Finally((source, destination) => destination.Name = $"{source.Name} {source.Year}");
    }
  }
}

internal class Destination
{
  public string Name { get; set; }
}

public class Source
{
  public string Name { get; set; }
  public int Year { get; set; }
}

Per-member customization

When a destination object change involves multiple member changes, it can be split to improve configuration readability and simplify maintenance.

using FluentAssertions;
using Xunit;

public class Example
{
  [Fact]
  public void Test()
  {
    var source = new Source { Name = "Foo", Year = 2024, Cost = 100 };
    var destination = source.MapToDestination();
    destination.Name.Should().Be("Bar");
    destination.Year.Should().Be(2023);
    destination.Cost.Should().Be(0);
  }

  internal class Configuration : IMapConfig
  {
    public void ConfigureMap(MapConfig config)
    {
      config
        .Map<Source>()
        .To<Destination>()
        .ForMember(d => d.Name, s => "Bar")
        .ForMember(d => d.Year, s => s.Year - 1)
        .ForMember(d => d.Cost, TransformCost);
    }

    // Note the class visibility access modifier, so `TransformCost` can be called
    public static decimal TransformCost(Source s) => 0;
  }
}

internal class Destination
{
  public string Name { get; set; }
  public int Year { get; set;  }
  public decimal Cost { get; set; }
}

public class Source
{
  public string Name { get; set; }
  public int Year { get; set; }
  public decimal Cost { get; set; }
}

Passing arguments

While it's possible to have value transformation logic defined in the map configuration, it can be extended by accepting additional parameters. To implement this, WithParameter should be defined, listing the arguments to be passed to the map configuration, as follows.

using FluentAssertions;
using Xunit;

public class Example
{
  [Fact]
  public void Test()
  {
    var source = new Source { Name = "Foo" };
    var destination = source.MapToDestination("Bar");
    destination.Name.Should().Be("Bar");
  }

  private class Configuration : IMapConfig
  {
    public void ConfigureMap(MapConfig config)
    {
      config
        .Map<Source>()
        .To<Destination>()
        .WithParameter<string>()
        .ConstructFrom((source, prm) => new Destination { Name = prm })
        .Ignore(m => m.Name);
    }
  }
}

internal class Destination
{
  public string Name { get; set; }
}

public class Source
{
  public string Name { get; set; }
}

In case of multiple parameters, the map configuration may look like the following.

private class Configuration : IMapConfig
{
  public void ConfigureMap(MapConfig config)
  {
    config
      .Map<Source>()
      .To<Destination>()
      .WithParameter<(string name, int year)>()
      .ConstructFrom((source, args) => new Destination { Name = $"{args.name} {args.year}" })
      .Ignore(m => m.Name);
  }
}

Handle lists and arrays

When a list of objects is being passed to the MapToDestination call, each item in the list is mapped according to the map configuration.

using FluentAssertions;
using Xunit;

public class Example
{
  [Fact]
  public void Test()
  {
    var sourceArray = new[]
    {
      new Source { Name = "Foo" },
      new Source { Name = "Bar" }
    };
    var destinationArray = sourceArray.MapToDestination();
    destinationArray.Select(d => d.Name).Should().ContainInOrder(sourceArray.Select(o => o.Name));
    
    var sourceList = new List<Source>
    {
      new() { Name = "Foo" },
      new() { Name = "Bar" }
    };
    var destinationList = sourceList.MapToDestination();
    destinationList.Select(d => d.Name).Should().ContainInOrder(sourceList.Select(o => o.Name));
  }

  private class Configuration : IMapConfig
  {
    public void ConfigureMap(MapConfig config)
    {
      config
      .Map<Source>()
      .To<Destination>();
    }
  }
}

internal class Destination
{
  public string Name { get; set; }
}

public class Source
{
  public string Name { get; set; }
}

Methods

Map

The Map method is used to specify the object to map.

public void ConfigureMap(MapConfig config)
{
  config.Map<Source>().To<Destination>();
}

💡 See related tutorial.

To

The To method is used to specify the object to map to.

public void ConfigureMap(MapConfig config)
{
  config
    .Map<Source>()
    .To<Destination>();
}

💡 See related tutorial.

From

The From method is used to specify the object to be mapped from.

public void ConfigureMap(MapConfig config)
{
  config
    .Map<Destination>()
    .From<Source>();
}

💡 See related tutorial.

WithDestinationNamingConvention

The WithDestinationNamingConvention method is used to specify naming convention rules to follow when attempting to identify matched members between source and destination objects.

public void ConfigureMap(MapConfig config)
{
  config
    .Map<Source>()
    .To<Destination>()
    .WithDestinationNamingConvention<PascalCaseConvention>();
}

💡 See related tutorial.

WithParameter

The WithParameter method is used to specify an argument or list of arguments that must be passed to perform object mapping.

public void ConfigureMap(MapConfig config)
{
  config
    .Map<Source>()
    .To<Destination>()
    .WithParameter<int>();
}

💡 See related tutorial.

ConstructFrom

The ConstructFrom method is used to specify how exactly the destination object should be created.

public void ConfigureMap(MapConfig config)
{
  config
    .Map<Source>()
    .To<Destination>()
    .ConstructFrom(source => new Destination { Name = "Name always Foo" });
}

💡 See related tutorial.

Finally

The Finally method is used to specify an action to be performed after the object is created.

public void ConfigureMap(MapConfig config)
{
  config
    .Map<Source>()
    .To<Destination>()
    .Finally((source, destination) =>
    {
      source.Name = "Change source name";
      destination.Name = "Change destination name";
    });
}

💡 See related tutorial.

ForMember

The ForMember method is used to specify an action to be performed on a member during mapping.

public void ConfigureMap(MapConfig config)
{
  config
    .Map<Source>()
    .To<Destination>()
    .ForMember(member => member.Name, sourceValue => $"Copied from {sourceValue}");
}

💡 See related tutorial.

Ignore

The Ignore method is used to specify a member to exclude from mapping.

public void ConfigureMap(MapConfig config)
{
  config
    .Map<Source>()
    .To<Destination>()
    .Ignore(member => member.Name);
}

💡 See related tutorial.

WithMappingMode

The WithMappingMode method is used to specify object member types to include in the mapping while excluding others.

public void ConfigureMap(MapConfig config)
{
  config
    .Map<Source>()
    .To<Destination>()
    .WithMappingMode(SourceMappingMode.MapMethods);
}

💡 See related tutorial.

Attributes

MapTo

The [MapTo] attribute is used to specify the object to map to.

[MapTo(typeof(Destination))]
public class Source
{
  public string Name { get; set; }
}

💡 See related tutorial.

MapFrom

The [MapFrom] attribute is used to specify the object to map from.

[MapFrom(typeof(Source))]
internal class Destination
{
  public string Name { get; set; }
}

💡 See related tutorial.

Ignore

The [Ignore] attribute is used to specify a member to exclude from mapping.

[MapFrom(typeof(Source))]
internal class Destination
{
  public string Name { get; set; }
  [Ignore]
  public int Year { get; set; }
}

The [Ignore] attribute [For] is used to specify the type from which the member mapping should be excluded.

[MapFrom(typeof(Source))]
internal class Destination
{
  public string Name { get; set; }
  [Ignore(For = typeof(Source))]
  public int Year { get; set; }
}

💡 See related tutorial.

DestinationMembersNamingConvention

The [DestinationMembersNamingConvention] attribute is used to specify naming convention rules to follow when attempting to identify matching members between source and destination objects.

[MapFrom(typeof(Source), DestinationMembersNamingConvention = typeof(PascalCaseConvention))]
internal class Destination
{
  public string Name { get; set; }
}

💡 See related tutorial.

DestinationConstructorNamingConvention

The [DestinationConstructorNamingConvention] attribute is used to specify naming convention rules that should be followed when attempting to resolve constructor parameters.

[MapFrom(typeof(source),
  DestMappingMode = DestMappingMode.MapToConstructor,
  DestinationConstructorNamingConvention = typeof(CamelCaseConvention))]
internal class Destination
{
  public Destination(string firstName)
  {
    FirstName = firstName;
  }

  public string FirstName { get; }
}

💡 See related tutorial.

DestMappingMode

The [DestMappingMode] attribute is used to specify which members of the destination object should be mapped, such as properties, fields, and methods.

[MapFrom(typeof(Source), DestMappingMode = DestMappingMode.MapToPropsAndFields)]
internal class Destination
{
  public string Name { get; set; }
}

💡 See related tutorial.

SourceMappingMode

The [SourceMappingMode] attribute is used to specify which members of the source object to map, such as properties, fields, and methods.

[MapTo(typeof(Destination), SourceMappingMode = SourceMappingMode.MapPropsAndFields )]
public class Source
{
  public string Name { get; set; }
}

💡 See related tutorial.

Interfaces

IMapConfig

The IMapConfig interface declares the method that must be implemented to specify the map configuration.

private class Configuration : IMapConfig
{
  public void ConfigureMap(MapConfig config)
  {
    config
      .Map<Source>()
      .To<Destination>();
  }
}

💡 See related tutorial.

IMappable

The IMappable interface declares the method that must be implemented to specify the map configuration for the object.

internal class Destination : IMappable<Destination>
{
  public string Name { get; set; }
  
  public void ConfigureMap(MapConfig<Destination> map)
  {
    map.From<Source>();
  }
}

💡 See related tutorial.

Roadmap

  • Add custom naming support

See open issues for a full list of proposed features (and known issues).

License

Distributed under the MPL 2.0 License. See LICENSE for details.

Contribution

Contributions are what make the open source community such an amazing place to learn, inspire, and create. Any contributions you make are greatly appreciated.

If you have a suggestion that would make this better, please fork the repo and create a pull request. You can also simply open an issue with the tag "enhancement". Don't forget to give the project a star! Thanks again!

  1. Fork the Project
  2. Create your Feature Branch (git checkout -b feature/AmazingFeature)
  3. Commit your Changes (git commit -m 'Add some AmazingFeature')
  4. Push to the Branch (git push source feature/AmazingFeature)
  5. Open a Pull Request

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Convention-based object-to-object compile time mapper for .NET

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