Question

我在MSDN上关注this article。我将它移植到EF Code First。

public interface IUnitOfWork
{
    IRepository<Employee> Employees { get; }
    IRepository<TimeCard> TimeCards { get; }
    void Commit();
}

public class HrContext : DbContext
{
    public DbSet<Employee> Employees { get; set; }
    public DbSet<TimeCard> TimeCards { get; set; }
    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Employee>()
                    .HasMany(e => e.TimeCards)
                    .WithOptional(tc => tc.Employee);
     }
}

public class SqlRepository<T> : IRepository<T>
    where T : class
{
    private readonly DbSet<T> entitySet;
    public SqlRepository(DbContext context)
    {
        this.entitySet = context.Set<T>();
    }
    public void Add(T newEntity)
    {
        this.entitySet.Add(newEntity);
    }
    public IQueryable<T> FindAll()
    {
        return this.entitySet;
    }
    public T FindById(params object[] keys)
    {
        return this.entitySet.Find(keys);
    }
    public IQueryable<T> FindWhere(Expression<Func<T, bool>> predicate)
    {
        return this.entitySet.Where(predicate);
    }
    public void Remove(T entity)
    {
        this.entitySet.Remove(entity);
    }
}

public class SqlUnitOfWork : IUnitOfWork, IDisposable
{
    private readonly HrContext context;
    private IRepository<Employee> employees;
    private IRepository<TimeCard> timeCards;
    public SqlUnitOfWork()
    {
        this.context = new HrContext();
    }
    public IRepository<Employee> Employees
    {
        get
        {
            return new SqlRepository<Employee>(context);
        }
    }
    public IRepository<TimeCard> TimeCards
    {
        get
        {
            return new SqlRepository<TimeCard>(context);
        }
    }
    public void Commit()
    {
        this.context.SaveChanges();
    }
    public void Dispose()
    {
        context.Dispose();
    }
}

var query = from e in unitOfWork.Employees.FindAll()
            from tc in unitOfWork.TimeCards.FindAll()
            where tc.Employee.Id == e.Id && e.Name.StartsWith("C")
            select tc;
var timeCards = query.ToList();

这个模型很棒，因为它给了我可测试性。但是，像上面那样运行查询会抛出此

LINQ to Entities does not recognize the method
 'System.Linq.IQueryable`1[DomainModel.Models.TimeCard] FindAll()' 
  method, and this method cannot be translated into a store expression.

我理解错误但是有什么方法可以避免它但是仍然保留了可测试性的存储库吗？

Answer 1

由于IQueryable<T>和查询提供程序的工作方式，您的select语句无法翻译：请参阅此主题以获取更多信息What is the difference between IQueryable<T> and IEnumerable<T>?

您可以通过将表达式划分为单独的语句来“帮助”linq提供程序：

var ems = unitOfWork.Employees.FindAll();
var tcs = unitOfWork.TimeCards.FindAll();

var query = from e in ems
            from tc in tcs
            where tc.Employee.Id == e.Id && e.Name.StartsWith("C")
            select tc;

或者你可以让FindAll（）返回IEnumerable<T>而不是IQueryable<T>，然后你的原始表达式就可以了。

LINQ to Entities无法识别该方法

1 个答案: