如何使用 switch 语句匹配传递的泛型类型和 return object[]

Question

我是一名测试人员，略懂一点编程知识，但我无法让它工作。

我正在为我的集成测试 (BaseIntegrationTest.cs) 创建一个基础 class。它使用泛型来接受特定测试 class 所针对的 DbContext 和 Repository 类型。基础 class 设置数据库上下文和连接并创建适当 repository/controller classes.

的实例

    class BaseIntegrationTest <TContext, TRepo> where TContext : DbContext where TRepo : BaseRepository
    {
        ...

    }

除了每个测试可能唯一的DbContext和Repository类型class，我们还必须确定DatabaseConnectionString和目标存储库构造函数的签名class（因为发送到构造函数的参数数量可能会有所不同）。

我根据传递的泛型类型确定这些值。 TContext 定义了我使用的 DbConnectionString，TRepo 定义了要使用的 Repository 构造函数签名。为了定义这些东西，我添加了一个 private static inner class GenericTypeHelper。我的 BaseIntegrationTest class 看起来像这样...

...

namespace OurProduct.Tests.IntegrationTests
{
    class BaseIntegrationTest <TContext, TRepo> where TContext : DbContext where TRepo : BaseRepository
    {
        ...

        protected Dictionary<string, string> LocalDbConfig = new Dictionary<string, string>();
        protected TRepo Repository;

        [OneTimeSetUp]
        public void SetUp()
        {
            DefineLocalDbConfigs();
            SetupNewLocalDB();
            Repository = SetupRepository<TContext, TRepo>();
        }

        [OneTimeTearDown]
        public void TearDown()
        {
            TearDownLocalDB();
        }

        private void DefineLocalDbConfigs()
        {
            ...
            // define LocalDbConfig dictionary and add db configs
            ...
        }

        private void SetupNewLocalDB()
        {
            ...
            // set up LocalDb databases
            ...
        }

        public RepoType SetupRepository<DbContextType, RepoType>() where DbContextType : DbContext where RepoType : BaseRepository
        {
            var configBuilder = new ConfigurationBuilder();
            configBuilder.AddInMemoryCollection(LocalDbConfig);
            var configuration = configBuilder.Build();

            var dbBuilder = new DbContextOptionsBuilder<DbContextType>();
            dbBuilder.UseSqlServer(configuration.GetConnectionString(GenericTypeHelper.DbConnStringForDbContext[typeof(DbContextType)]));

            var context = (DbContextType)Activator.CreateInstance(typeof(DbContextType), new object[] { dbBuilder.Options });
            var logger = Mock.Of<ILogger<RepoType>>();
            var clock = new SystemClock();

            var commonLogger = Mock.Of<ILogger<CommonRepository>>();
            var commonRepo = new CommonRepository(configuration, commonLogger, clock);

            var repoConstrParamObjArr = GenericTypeHelper.GetRepoConstrParamObjArr(context, logger, clock, commonRepo);
            return (RepoType)Activator.CreateInstance(typeof(RepoType), repoConstrParamObjArr);
        }

        private void TearDownLocalDB()
        {
            foreach (var dbConnDefn in LocalDbConfig)
            {
                ...
                // open, set offline, close, dispose database
                ...
            }
        }

        private static class GenericTypeHelper
        {
            internal static readonly Dictionary<Type, string> DbConnStringForDbContext = new Dictionary<Type, string>
            {
                { typeof(DataContextA), "DB1" },
                { typeof(DataContextB), "DB2" },
                { typeof(DataContextC), "DB3" },
                { typeof(DataContextD), "DB1" },
                { typeof(DataContextE), "DB2" },
                { typeof(DataContextF), "DB3" }
            };

            internal static object[] GetRepoConstrParamObjArr<DbContextType, RepoType>(
                    DbContextType context,
                    ILogger<RepoType> logger,
                    SystemClock clock,
                    CommonRepository commonRepo)
                        where DbContextType : DbContext 
                        where RepoType : BaseRepository
                => typeof(RepoType) switch
                {
                    // these give compile error... CS0150: A constant value is expected
                    typeof(DataRepositoryA) => new object[] { context, logger, clock, commonRepo },
                    typeof(DataRepositoryB) => new object[] { context, logger, clock },
                    // these give compile error... CS8121: An expression of type 'Type' cannot be handled by a pattern of type 'DataRepositoryC'
                    DataRepositoryC         => new object[] { context, logger, clock, commonRepo },
                    DataRepositoryD         => new object[] { context, logger, clock },
                    _ => new object[] { }
                };

        }

    }
}

这个内部 class 给了我编译错误（如评论中所述），我尝试使用 switch 语句将通用 RepoType 与列出的可能存储库 class 进行比较将传递给 BaseIntegrationTest 的类型。有什么方法可以使用干净的开关功能来匹配通用类型吗？

Answer 1

虽然@Matthew Watson 的回答（在@The General 的帮助下）很聪明并且解决了我的编译问题，但它没有运行符合预期。 default(RepoType) returns 基本类型的正确类型的预期默认值，但对于非基本类型，它是 returns null。这意味着 switch 语句匹配默认值 _ => new object[] { }，而不管我通常传入哪个 RepoType。

不过，我确实通过使用 nameof() 找到了适合我需要的解决方案。

原始代码给我编译错误...

    internal static object[] GetRepoConstrParamObjArr<DbContextType, RepoType>(
            DbContextType context,
            ILogger<RepoType> logger,
            SystemClock clock,
            CommonRepository commonRepo)
                where DbContextType : DbContext 
                where RepoType : BaseRepository
        => typeof(RepoType) switch
        {
            // these give compile error... CS0150: A constant value is expected
            typeof(DataRepositoryA) => new object[] { context, logger, clock, commonRepo },
            typeof(DataRepositoryB) => new object[] { context, logger, clock },
            // these give compile error... CS8121: An expression of type 'Type' cannot be handled by a pattern of type 'DataRepositoryC'
            DataRepositoryC         => new object[] { context, logger, clock, commonRepo },
            DataRepositoryD         => new object[] { context, logger, clock },
            _ => new object[] { }
        };

按预期编译和运行s 的解决方案...

    internal static object[] GetRepoConstrParamObjArr<DbContextType, RepoType>(
            DbContextType context,
            ILogger<RepoType> logger,
            SystemClock clock,
            CommonRepository commonRepo)
                where DbContextType : DbContext 
                where RepoType : BaseRepository
        => typeof(RepoType).Name switch
        {
            nameof(DataRepositoryA) => new object[] { context, logger, clock, commonRepo },
            nameof(DataRepositoryB) => new object[] { context, logger, clock },
            nameof(DataRepositoryC) => new object[] { context, logger, clock, commonRepo },
            nameof(DataRepositoryD) => new object[] { context, logger, clock },
            _                       => new object[] { }
        };

如何使用 switch 语句匹配传递的泛型类型和 return object[]

How to use switch statement to match against passed generic type and return object[]

c#

generics

types

switch-statement