在Minimal API中使用AutoMapper报错：缺少类型映射配置如何解决？

我在连接Cosmos DB的新Minimal API项目中尝试使用AutoMapper，当获取所有对象时出现错误：“Missing type map configuration or unsupported mapping”，请问问题出在哪里？

相关代码 #

CarRequests类

public static class CarRequests
{
    public static WebApplication CarEndpoints(this WebApplication app)
    {
        app.MapGet("/cars", CarRequests.GetAll);
        return app;
    }

    public static IResult GetAll(ICarService service, IMapper mapper)
    {
        var cars = service.GetAll();
        var result = mapper.Map<List<CarDto>>(cars);
        return Results.Ok(result);
    }
}

Car类

public class Car
{
    [JsonProperty(PropertyName = "id")]
    public string Id { get; set; }
    [JsonProperty(PropertyName = "producent")]
    public Producent Producent { get; set; }
    [JsonProperty(PropertyName = "age")]
    public int Age { get; set; }
    [JsonProperty(PropertyName = "yearCreated")]
    public int YearCreated { get; set; }
    [JsonProperty(PropertyName = "engine")]
    public Engine Engine { get; set; }

    public Car()
    {
        Id= Guid.NewGuid().ToString();
        YearCreated = DateTime.Now.Year - Age;
    }
}

Engine类

public class Engine
{
    [JsonProperty(PropertyName = "id")]
    public string Id { get; set; }
    [JsonProperty(PropertyName = "horsePower")]
    public int HorsePower { get; set; }
    [JsonProperty(PropertyName = "description")]
    public string Description { get; set; }

    public Engine()
    {
        Id= Guid.NewGuid().ToString();
    }
}

EngineDto类

public class EngineDto
{
    [JsonProperty(PropertyName = "horsePower")]
    public int HorsePower { get; set; }
    [JsonProperty(PropertyName = "description")]
    public string Description { get; set; }
}

CarDto类

public class CarDto
{
    [JsonProperty(PropertyName = "producent")]
    public Producent Producent { get; set; }
    [JsonProperty(PropertyName = "age")]
    public int Age { get; set; }
    [JsonProperty(PropertyName = "yearCreated")]
    public EngineDto Engine { get; set; }
}

服务类GetAll方法

public async Task<IEnumerable<Car>> GetAll()
{
    string queryString = "select * from c";

    var feedIterator = _container.GetItemQueryIterator<Car>(new QueryDefinition(queryString));
    List<Car> cars = new List<Car>();

    while (feedIterator.HasMoreResults)
    {
        var response = await feedIterator.ReadNextAsync();
        cars.AddRange(response.ToList());
    }
    return cars;
}

AutoMapper配置类

public class AutoMapperProfile:Profile
{
    public AutoMapperProfile()
    {
        CreateMap<Car, CarDto>();
        CreateMap<Engine, EngineDto>();
        CreateMap<CarDto, Car>();
        CreateMap<EngineDto, Engine>();
    }
}

Program.cs中的AutoMapper注册

builder.Services.AddAutoMapper(AppDomain.CurrentDomain.GetAssemblies());

导致错误的核心原因有两个：

1. 异步方法未正确等待 #

你的GetAll服务方法返回的是Task<IEnumerable<Car>>，但在CarRequests.GetAll中直接调用service.GetAll()而没有加await，这意味着你传给AutoMapper的是一个Task对象，而不是实际的IEnumerable<Car>集合。AutoMapper没有配置从Task到List<CarDto>的映射，因此抛出错误。

修正方法：
将CarRequests.GetAll改为异步方法，添加await获取实际数据：

public static async Task<IResult> GetAll(ICarService service, IMapper mapper)
{
    var cars = await service.GetAll();
    var result = mapper.Map<List<CarDto>>(cars);
    return Results.Ok(result);
}

2. CarDto属性的JsonProperty标注错误 #

在CarDto中，你将Engine属性的JsonProperty标记为"yearCreated"，但对应的Car类中：

• YearCreated是int类型字段，对应"yearCreated"
• Engine是Engine类型字段，对应"engine"

这种标注错误会导致AutoMapper无法正确匹配属性，进而引发映射配置缺失的错误。

修正方法：
修正CarDto的JsonProperty标注，同时如果需要返回YearCreated字段，添加对应的属性：

public class CarDto
{
    [JsonProperty(PropertyName = "producent")]
    public Producent Producent { get; set; }
    [JsonProperty(PropertyName = "age")]
    public int Age { get; set; }
    [JsonProperty(PropertyName = "yearCreated")]
    public int YearCreated { get; set; }
    [JsonProperty(PropertyName = "engine")]
    public EngineDto Engine { get; set; }
}

3. 额外验证（可选） #

确认你的AutoMapperProfile所在的程序集被正确扫描到，你当前的注册方式AddAutoMapper(AppDomain.CurrentDomain.GetAssemblies())已经覆盖了所有程序集，只要AutoMapperProfile在项目程序集中，就会被自动加载，这部分通常无需调整。

完成以上修正后，重新运行项目，映射错误应该会被解决。

内容的提问来源于stack exchange，提问作者Ptrk12