具有 nHibernate 的通用存储库

我目前有这个类为我的通用存储库组成

public abstract class RepositoryBase<T> where T : class
{
    private readonly ISession session;
    public RepositoryBase(ISession session)
    {
        this.session = session;
        this.session.FlushMode = FlushMode.Auto;
    }
    public void Start()
    {
        this.session.BeginTransaction();
    }
    public bool Add(T entity)
    {
        this.session.Save(entity);
        return true;
    }
    public bool AddAll(IEnumerable<T> items)
    {
        foreach (T item in items)
        {
            this.session.Save(item);
        }
        return true;
    }
    public bool Update(T entity)
    {
        this.session.Flush();
        this.session.Update(entity);
        return true;
    }
    public bool Delete(T entity)
    {
        this.session.Delete(entity);
        return true;
    }
    public bool DeleteAll(IEnumerable<T> entities)
    {
        foreach (T entity in entities)
        {
            this.Delete(entity);
        }
        return true;
    }
    public T GetById(int id)
    {
        return this.session.Get<T>(id);
    }
    public T GetById(string id)
    {
        return this.session.Get<T>(id);
    }
    public T GetById(long id)
    {
        return this.session.Get<T>(id);
    }
    public T GetById(Guid id)
    {
        return this.session.Get<T>(id);
    }
    public IQueryable<T> GetAll()
    {
        return this.session.Query<T>();
    }
    public T Get(Expression<System.Func<T, bool>> expression)
    {
        return GetMany(expression).SingleOrDefault();
    }
    public IQueryable<T> GetMany(Expression<System.Func<T, bool>> expression)
    {
        return GetAll().Where(expression).AsQueryable();
    }
}

当我调用采用字符串参数的 GetById 方法时，我遇到了异常错误，指出 GetById 需要类型 Guid 而不是字符串。如何设计此方法以接受字符串参数？

public abstract class Repository<T, TId>
{
    public T Get(TId id)
    {
    }
}