如何在 ASP.NET Core Web API 中处理 Patch 请求

public class PersonInput
{
    public string? Name { get; set; }
    public int? Age { get; set; }
    public string? Gender { get; set; }
}
public class PersonEntity
{
    public string Name { get; set; }
    public int Age { get; set; }
    public string Gender { get; set; }
}

[HttpPatch]
[Route("patch")]
public ActionResult Patch([FromForm] PersonInput input)
{
    // 测试代码暂时将 AutoMapper 配置放在方法内。
    var config = new MapperConfiguration(cfg =>
    {
        cfg.CreateMap<PersonInput, PersonEntity>());
    });
    var mapper = config.CreateMapper();
    // entity 从数据库读取，这里仅演示。
    var entity = new PersonEntity
    {
        Name = "姓名", // 可能会被改变
        Age = 18, // 可能会被改变
        Gender = "我可能会被改变",
    };
    // 如果客户端只输入 Name 字段，entity 的 Age 和 Gender 将不能被正确映射或被置为 null。
    mapper.Map(input, entity);
    return Ok();
}

curl --location --request PATCH 'http://localhost:5094/test/patch' \
--form 'Name="foo"'

var keys = _httpContextAccessor.HttpContext.Request.Form.Keys;
if(keys.Contains("Name"))
{
    // 更新 Name(这里忽略合法性判断)
    entity.Name = input.Name!;
}
if (keys.Contains("Age"))
{
    // 更新 Age(这里忽略合法性判断)
    entity.Age = input.Age!;
}
// ...

public abstract class PatchInput
{
    [BindNever]
    public ICollection<string>? PatchKeys { get; set; }
}

public class PersonInput : PatchInput
{
    public string? Name { get; set; }
    public int? Age { get; set; }
    public string? Gender { get; set; }
}

public class PatchModelBinder : IModelBinder
{
    private readonly IModelBinder _internalModelBinder;
    public PatchModelBinder(IModelBinder internalModelBinder)
    {
        _internalModelBinder = internalModelBinder;
    }
    public async Task BindModelAsync(ModelBindingContext bindingContext)
    {
        await _internalModelBinder.BindModelAsync(bindingContext);
        if (bindingContext.Model is PatchInput model)
        {
            // 将 Form 中的 Keys 保存在 PatchKeys 中
            model.PatchKeys = bindingContext.HttpContext.Request.Form.Keys;
        }
    }
}

public class PatchModelBinderFactory : IModelBinderFactory
{
    private ModelBinderFactory _modelBinderFactory;
    public PatchModelBinderFactory(
        IModelMetadataProvider metadataProvider,
        IOptions<MvcOptions> options,
        IServiceProvider serviceProvider)
    {
        _modelBinderFactory = new ModelBinderFactory(metadataProvider, options, serviceProvider);
    }
    public IModelBinder CreateBinder(ModelBinderFactoryContext context)
    {
        var modelBinder = _modelBinderFactory.CreateBinder(context);
        // ComplexObjectModelBinder 是 internal 类
        if (typeof(PatchInput).IsAssignableFrom(context.Metadata.ModelType)
            && modelBinder.GetType().ToString().EndsWith("ComplexObjectModelBinder"))
        {
            modelBinder = new PatchModelBinder(modelBinder);
        }
        return modelBinder;
    }
}

var builder = WebApplication.CreateBuilder(args);
// Add services to the container.
builder.Services.AddPatchMapper();

public static class PatchMapperExtensions
{
    public static IServiceCollection AddPatchMapper(this IServiceCollection services)
    {
        services.Replace(ServiceDescriptor.Singleton<IModelBinderFactory, PatchModelBinderFactory>());
        return services;
    }
}

[HttpPatch]
[Route("patch")]
public ActionResult Patch([FromForm] PersonInput input)
{
    // 不需要手工给 input.PatchKeys 赋值。
    return Ok();
}

public class PatchConverter<T> : ITypeConverter<PatchInput, T> where T : new()
{
    /// <inheritdoc />
    public T Convert(PatchInput source, T destination, ResolutionContext context)
    {
        destination ??= new T();
        var sourceType = source.GetType();
        var destinationType = typeof(T);
        foreach (var key in source.PatchKeys ?? Enumerable.Empty<string>())
        {
            var sourcePropertyInfo = sourceType.GetProperty(key, BindingFlags.IgnoreCase | BindingFlags.Public | BindingFlags.Instance);
            if (sourcePropertyInfo != null)
            {
                var destinationPropertyInfo = destinationType.GetProperty(key, BindingFlags.IgnoreCase | BindingFlags.Public | BindingFlags.Instance);
                if (destinationPropertyInfo != null)
                {
                    var sourceValue = sourcePropertyInfo.GetValue(source);
                    destinationPropertyInfo.SetValue(destination, sourceValue);
                }
            }
        }
        return destination;
    }
}

[HttpPatch]
[Route("patch")]
public ActionResult Patch([FromForm] PersonInput input)
{
    // 1. 目前仅支持 `FromForm`，即 `x-www-form_urlencoded` 和 `form-data`；暂不支持 `FromBody` 如 `raw` 等。
    // 2. 使用 ModelBinderFractory 创建 ModelBinder 而不是 ModelBinderProvider 以便于未来支持更多的输入格式。
    // 3. 目前还没有支持多级结构。
    // 4. 测试代码暂时将 AutoMapper 配置放在方法内。
    var config = new MapperConfiguration(cfg =>
    {
        cfg.CreateMap<PersonInput, PersonEntity>().ConvertUsing(new PatchConverter<PersonEntity>());
    });
    var mapper = config.CreateMapper();
    // PersonEntity 有 3 个属性，客户端如果提供的参数参数不足 3 个，在 Map 时未提供参数的属性值不会被改变。
    var entity = new PersonEntity
    {
        Name = "姓名",
        Age = 18,
        Gender = "如果客户端没有提供本参数，那我的值不会被改变"
    };
    mapper.Map(input, entity);
    return Ok();
}

curl --location --request PATCH 'http://localhost:5094/test/patch' \
--form 'Name="foo"'

curl --location --request PATCH 'http://localhost:5094/test/patch' \
--header 'Content-Type: application/x-www-form-urlencoded' \
--data-urlencode 'Name=foo'