LINQ - 当值为NULL时排除过滤器

Question

当有一个可选参数（CountryId）可以为NULL时，我试图看看是否有更好的方法来编写下面的查询

 public static IEnumerable<Game> GameByMatchingName(this IRepositoryAsync<Game> repository,  string searchCriteria, string countryId = null)
        {
            return repository
                .Queryable()
                .Where(x => (countryId != null ? x.CountryId == countryId : true) && x.Name.Contains(searchCriteria))
                .AsEnumerable();
        }

理想情况下，我想在CountryId为NULL时排除过滤器中的条件。

-Alan -

Answer 1

public static IEnumerable<Game> GameByMatchingName(this IRepositoryAsync<Game> repository,  string searchCriteria, string countryId = null)
    {
        return repository
            .Queryable()
            .Where(x => (countryId == null) || (x.CountryId == countryId && x.Name.Contains(searchCriteria)).AsEnumerable();
    }

Answer 2

无法按步骤构建它：

public static IEnumerable<Game> GameByMatchingName(this IRepositoryAsync<Game> repository,  string searchCriteria, string countryId = null)
    {
         var ret = repository
          .Queryable()
            .Where(x=>x.Name.Contains(searchCriteria));

          if (!(countrId == null))
          {
             ret = ret.Where(y=>y.CountryId == countryId )
          }
         return ret.AsEnumerable();;
     }