如何创建一个字典，其中键是一天，值是对象列表

Question

我有以下对象：

public class ExchangeRate
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int Id { get; set; }

    [Required]
    [Min(0)]
    public double Value { get; set; }

    [Required]
    public DateTime ValidFrom { get; set; } = DateTime.Now;

    [MaxLength(3)]
    [Required]
    public int CurrencyId { get; set; }
    public virtual CurrencyDto Currency { get; set; }
}

我需要从 ExchangeRate 类型列表中创建一个字典，其中键是 ValidFrom 中的 day 属性，字典中的值是 Exchange 对象列表，其中 ValidFrom 属性 day 属性等于键。

这是我尝试过的：

var exchangeRates = dbContext.ExchangeRates.Where(x => x.ValidFrom.Year == DateTime.Now.Year)
                                           .Where(x => x.ValidFrom.Month == DateTime.Now.Month)
                                           .Where(x => x.ValidFrom.Day >= day)
                                           .GroupBy(k => k.ValidFrom.Day, v => v)
                                           .ToDictionary(x => x.Key, x => x.ToList());

我收到以下错误：

System.InvalidOperationException：LINQ 表达式 'DbSet() .Where(x => x.ValidFrom.Year == DateTime.Now.Year) .Where(x => x.ValidFrom.Month == DateTime.Now.Month) 。 Where(x => x.ValidFrom.Day >= __day_0) .GroupBy(keySelector: k => k.ValidFrom.Day, elementSelector: v => v)' 无法翻译。 以可翻译的形式重写查询，或通过插入对“AsEnumerable”、“AsAsyncEnumerable”、“ToList”或“ToListAsync”的调用显式切换到客户端评估。

谢谢

Answer 1

这就是我最后解决的方法：

        var exchangeRates = await dbContext.ExchangeRates.Where(x => x.ValidFrom.Year == DateTime.Now.Year)
                                                         .Where(x => x.ValidFrom.Month == DateTime.Now.Month)
                                                         .Where(x => x.ValidFrom.Day >= day)
                                                         .GroupBy(k => k.ValidFrom.Day, v => v)
                                                         .Select(x => new KeyValuePair<int, List<ExchangeRateDto>>(x.Key, x.ToList()))
                                                         .ToDictionaryAsync(x => x.Key, x => x.Value);