无法使用异步从 Type ICollection 转换为 List

Question

我在服务中有以下代码：

var countriesTask = countryIds != null && countryIds.Any()
                                    ? this.dataContext.Countries.Where(c => countryIds.Contains(c.CountryId)).ToListAsync()
                                    : Task.FromResult(new List<Country>());
        var countries = await countriesTask;

我想通过创建 RepositoryBase 来重构依赖 Datacontext class:

IRepositoryBase:
    Task<ICollection<T>> FindAllAsync(Expression<Func<T, bool>> match);

RepositoryBase:
    public virtual async Task<ICollection<T>> FindAllAsync(Expression<Func<T, bool>> match)
    {
        return await this.DbContext.Set<T>().Where(match).ToListAsync();
    }

然后将上面的重构为：

   var countriesTask = countryIds != null && countryIds.Any()
                                ? this.countryRepository.FindAllAsync(c => countryIds.Contains(c.CountryId))
                                : Task.FromResult(new List<Country>());
   var countries = await countriesTask;

我收到类型转换错误（无法从 Type ICollection Country 转换为 Type List Country，今天早上我的大脑不工作。我知道可能是 ToListAsync 引起了问题，但每个当我改变某些东西时，其他东西坏了！我该怎么办

Answer 1

在我看来你只需要这样做：

var countriesTask =
    countryIds != null && countryIds.Any()
    ? this.countryRepository.FindAllAsync(c => countryIds.Contains(c.CountryId))
    : Task.FromResult<ICollection<Country>>(new List<Country>());

基本上?:两边的运算符需要return相同的类型。您的代码试图 return Task<ICollection<Country>> & Task<List<Country>>。通过使 return Task<ICollection<Country>> 它应该可以正常工作。

无法使用异步从 Type ICollection 转换为 List

Can't convert from Type ICollection to List with async

c#

repository-pattern