EntityFramework、DbContextScope和Effort - 异常：在单元测试中DbContext已被释放

Question

我正在尝试使用NUnit编写服务层的单元测试，该层使用以下内容：

1. Entity Framework作为数据访问层
2. DbContextScope用于管理DbContext生命周期

我还使用Effort.EF6来模拟单元测试中的DbContext。不幸的是，我找不到一种方法使DbContextScope与Effort兼容，以便我可以正确地测试所有情况。

---

代码概述 服务层由执行某些业务逻辑的类（服务）组成。每个方法都被视为一个完整的事务，并以context.SaveChanges()结束。例如：

    private IDbContextScopeFactory _dbContextScopeFactory;

    public DepartmentsService(IDbContextScopeFactory dbContextScopeFactory)
    {
        _dbContextScopeFactory = dbContextScopeFactory;
    }

    public BusinessModel.Department Insert(BusinessModel.Department department)
    {
        using (var dbContextScope = _dbContextScopeFactory.Create())
        {
            // Validation
            ValidateAndThrowOnFailure(department, new DepartmentAddValidator());

            // Operation
            DBModel.Department newDepartment = Mapper.Map<DBModel.Department>(department);

            newDepartment.InsertDateUTC = DateTime.UtcNow;

            dbContextScope.DbContexts.Get<DPSContext>().Departments.Add(newDepartment);
            dbContextScope.SaveChanges();

            return Mapper.Map<BusinessModel.Department>(newDepartment);
        }
    }

为了对这种方法进行单元测试，在每个测试之前我都要做一些准备工作：

    private IDepartmentsService _departmentsService;
    private IDbContextScopeFactory _dbContextScopeFactory;
    private IDbContextFactory _dbContextFactory;
    private DBModel.DPSContext _dbEntities;

    [SetUp]
    public void ReInitializeTest()
    {
        // Setup DbContext with Effort.EF6
        string connStr = ConfigurationManager.ConnectionStrings["DPSContext"].ConnectionString;
        DbConnection connection = EntityConnectionFactory.CreateTransient(connStr);
        _dbEntities = new DBModel.DPSContext(connection);

        // Fill DbContext with in-memory data
        _dbEntities.Departments.AddRange(DataInitializer.GetDepartments());
        _dbEntities.SaveChanges();

        // Mock IDbContextFactory so that it returns in-memory context
        var contextFactoryMock = new Mock<IDbContextFactory>();

        contextFactoryMock
            .Setup(f => f.CreateDbContext<DBModel.DPSContext>())
            .Returns(_dbEntities);

        _dbContextFactory = contextFactoryMock.Object;

        // Setup DbContextScopeFactory to use mocked context
        _dbContextScopeFactory = new DbContextScopeFactory(_dbContextFactory);
        _departmentsService = new DepartmentsService(_dbContextScopeFactory);
    }

---

测试和问题

这是一个简单的单元测试：

    [Test]
    public void Insert_WhenValidModelPassed_ShouldInsertNewRecord()
    {
        // Given
        BusinessModel.Department newDepartment = DataInitializer.GetExampleOfNewDepartment();

        // When
        _departmentsService.Insert(newDepartment);

        // Then
        Assert.AreEqual(3, _dbEntities.Departments.Count());
    }

问题在于测试失败并出现异常：

System.InvalidOperationException : The operation cannot be completed because the DbContext has been disposed.

似乎在Insert方法中使用的DbContextScope会在using块结束时内部释放已分配的上下文，因此当调用Assert时会抛出异常。是否有人遇到过类似的问题或知道我应该怎么做才能成功测试这种和类似情况？

- PJDev

Answer 1

如果有人遇到了类似的问题，我已经创建了一个有点“肮脏但可行”的解决方案（至少我希望如此）。除了我在问题中写的内容，我创建了一个派生自真实上下文的类，并使Dispose方法什么也不做。我还添加了一个RealDispose方法，在每个测试结束时调用。

    public class TestableDPSContext : DBModel.DPSContext
    {
        public TestableDPSContext(DbConnection connection)
            : base(connection)
        {

        }

        protected override void Dispose(bool disposing)
        {
            // Do nothing
        }

        public void RealDispose(bool disposing)
        {
            // Invoke real dispose
            base.Dispose(disposing);
        }
    }

    [TearDown]
    public void FinishTest()
    {
        _dbEntities.RealDispose(false);
    }

也许还有更好的解决方案，但目前似乎可以解决测试中DbContext过早被释放的问题。

- PJDev