如何在DDD存储库中使用包含值对象类型进行过滤?

Question

我用DDD方法开发了一个项目来管理假期。我有两个值对象的名字是HolidayTitle和HolidayDate。现在我想在查询存储库中过滤包含，但我不能。

我在仓库中的代码如下:

public async Task<ListResponse<IList<GetHolidaysByDatesDto>>> GetHolidays(GetHolidaysQuery param)
        {
            var query = _repository.AsQueryable();
            if (param.Date.HasValue)
                query = query.Where(x => x.Date == param.Date);
            if (!string.IsNullOrEmpty(param.Title))
                query = query.Where(x => x.Title.Contains(param.Title));
            var pagingData = await query.GetPagingData(param);
            query = query.SetPaging(param);
            var holidays = await query.ToListAsync();
            var mappedResult = _mapper.Map<IList<GetHolidaysByDatesDto>>(holidays);
            var finalResult = new ListResponse<IList<GetHolidaysByDatesDto>>()
            {
                PageCount = pagingData.PageCount,
                PageNumber = pagingData.PageNumber,
                RowCount = pagingData.RowCount,
                Result = mappedResult
            };
            return finalResult;
        }

和HolidayTitle的代码如下

public class HolidayTitle : BaseValueObject<HolidayTitle>
    {
        public static readonly int minLength = 5;
        public static readonly int maxLength = 300;
        public string Value { get; private set; }
        private HolidayTitle(string value)
        {
            if (value is null)
                throw new NullOrEmptyArgumentException(HolidayErrors.HolidayTitleIsNull);
            value = value.Trim();
            if (value == string.Empty)
                throw new NullOrEmptyArgumentException(HolidayErrors.HolidayTitleIsEmpty);
            if (value.Length > maxLength || value.Length < minLength)
                throw new RangeLengthArgumentException(HolidayErrors.HolidayTitleLengthIsNotInRangeLength, minLength.ToString(), maxLength.ToString());
            Value = value;
        }
        public bool Contains(string str)
        {
            return Value.Contains(str);
        }
        public override bool IsEqual(HolidayTitle otherObject)
        {
            return Value == otherObject.Value;
        }
        public override int ObjectGetHashCode()
        {
            return Value.GetHashCode();
        }
        public static implicit operator string(HolidayTitle value)
        {
            return value.Value;
        }
        public static HolidayTitle GetInstance(string value)
        {
            return new(value);
        }
    }

我得到这个错误

System.InvalidOperationException: 'The LINQ expression 'DbSet<Holiday>()
.Where(h => !(h.IsDeleted))
.Where(h => h.Title.Contains(__param_Title_0))' could not be translated. Additional information: Translation of method 'Core.Domain.Holidays.ValueObjects.HolidayTitle.Contains' failed. If this method can be mapped to your custom function, see https://go.microsoft.com/fwlink/?linkid=2132413 for more information. Either rewrite the query in a form that can be translated, or switch to client evaluation explicitly by inserting a call to 'AsEnumerable', 'AsAsyncEnumerable', 'ToList', or 'ToListAsync'. See https://go.microsoft.com/fwlink/?linkid=2101038 for more information.'

Answer 1

EF无法将其转换为查询。有一种方法可以将整个数据加载到内存中，然后对其进行过滤。

您必须使用下面的，因为query是IQueryable:

query.AsEnumerable()
     .Where......

Answer 2

不能写

     query = query.Where(x => x.Title.Contains(param.Title));

因为EF不知道你的HolidayTitle.Contains方法

另一方面，EF知道如何翻译方法string.Contains:

     query = query.Where(x => x.Title.Value.Contains(param.Title));