c# - 在构造函数中使用 Mapper.Initialize

Question

我正在使用 AutoMapper 将 POCO 映射到 DTO。 为了实现单元可测试性，我将 IMapping 引擎传递到构造函数中，并在构造函数为 null 的情况下使用 Mapper.Initialize。

public class PeopleEfProvider : IPeopleDbContext
{
    public IMappingEngine MappingEngine { get; set; }
    public DatabaseHelpersRepo DatabaseHelpersRepo { get; set; }
    public PeopleDataContext DataContext { get; set; }
    public PeopleEfProvider(PeopleDataContext dataContext = null, IMappingEngine mappingEngine = null)
    {
        DataContext = dataContext ?? new PeopleDataContext();
        // if mappingEngine is coming from Unit Test or from another Client then use it.
        if (mappingEngine == null)
        {               
            Mapper.Initialize(mapperConfiguration =>
            {
                mapperConfiguration.AddProfile(new PeopleEfEntityProfile());
            });
            Mapper.AssertConfigurationIsValid();
            MappingEngine = Mapper.Engine;
        }
        else
        {
            MappingEngine = mappingEngine;
        }
        DatabaseHelpersRepo = new DatabaseHelpersRepo(DataContext, MappingEngine);
    }
}

以这种方式使用 AutoMapper 有什么缺点吗？我运行了超过 1000 个循环的集成测试，没有发现任何问题，另一方面，我不能说当我把它放到网上时它是否可行。

AutoMapper 是否会在下一个对象创建时尝试从头开始构建所有映射，或者它是否足够智能，不会再次映射相同的对象？

Answer 1

每个 AppDomain 只能调用一次 Mapper.Initialize，如果您不只是在应用程序启动时(App_Start 等)调用它，您将会遇到一些不稳定的线程问题。

您还可以创建一个惰性初始化程序来完成同样的事情:

public class PeopleEfProvider : IPeopleDbContext
{
    private static Lazy<IMappingEngine> MappingEngineInit = new Lazy<IMappingEngine>(() => {
        Mapper.Initialize(mapperConfiguration =>
        {
            mapperConfiguration.AddProfile(new PeopleEfEntityProfile());
        });
        Mapper.AssertConfigurationIsValid();
        return Mapper.Engine;
    });
    public IMappingEngine MappingEngine { get; set; }
    public DatabaseHelpersRepo DatabaseHelpersRepo { get; set; }
    public PeopleDataContext DataContext { get; set; }
    public PeopleEfProvider(PeopleDataContext dataContext = null, IMappingEngine mappingEngine = null)
    {
        DataContext = dataContext ?? new PeopleDataContext();
        MappingEngine = mappingEngine ?? MappingEngineInit.Value;
        DatabaseHelpersRepo = new DatabaseHelpersRepo(DataContext, MappingEngine);
    }
}