Question

我在我的基础仓库里有一个这样的方法。

public async Task<TEntity> GetByCondition(Expression<Func<TEntity, bool>> predicate, Func<DbSet<TEntity>, IQueryable<TEntity>> baseQuery = null, Expression<Func<TEntity, TEntity>> projection = null)
        {
            IQueryable<TEntity> q = _context.Set<TEntity>();

            if (baseQuery != null)
            {
                q = baseQuery(_context.Set<TEntity>());
            }
        if (projection != null)
        {
            q = q.Select(projection);
        }

        return await q.Where(predicate).FirstOrDefaultAsync();
    }

我试着调用这个方法，就像这样

Expression<Func<Businesses, bool>> predicate = x => x.Id == id && x.Status == (int)EnumGringo.LU_Status.active;

            IQueryable<Businesses> baseQuery(DbSet<Businesses> x) => x.Include(c => c.BusinessDetails)
                                                                      .Include(c => c.BusinessFacilities).ThenInclude(c => c.Facility)
                                                                      .Include(c => c.BusinessImages);


            Expression<Func<Businesses, Businesses>> projection = x => new Businesses
            {
                BusinessDetails = x.BusinessDetails.Where(bd => bd.Status == (int)EnumGringo.LU_Status.active && bd.LanguageTypeId == (int)EnumGringo.Lu_LanguageTypes.he).ToList(),
                Name = "Name projection"
            };

            Businesses business = await _repository.GetByCondition(predicate, baseQuery, projection);

在这个阶段，我得到一个错误，比如：

类型为 "System.Collections.Generic.IAsyncEnumerable "的表达式。

1[DAL.Models.BusinessDetails]'
  cannot be used for parameter of type
  'System.Collections.Generic.IEnumerable

1[DAL.Models.BusinessDetails]"的方法'System.Collections.Generic.List

1[DAL.Models.BusinessDetails]
  ToList[BusinessDetails](System.Collections.Generic.IEnumerable

1[DAL.Models.BusinessDetails])'。

所以我有2个问题。1) 我如何让它工作？2) 如果我发送投射参数或者像这样过滤我的实体，有什么区别吗？

Businesses business = await _repository.GetByCondition(predicate, baseQuery);
            business.BusinessDetails = business.BusinessDetails.Where(bd => bd.Status == (int)EnumGringo.LU_Status.active && bd.LanguageTypeId == (int)EnumGringo.Lu_LanguageTypes.he).ToList();

Answer 1

问题就在这里。

        if (projection != null)
        {
            q = q.Select(projection);
        }

        return await q.Where(predicate).FirstOrDefaultAsync();

试着先过滤一下 IQuerable 然后得到这样的投影。

        q = q.Where(predicate);
        if (projection != null)
        {
            q = q.Select(projection);
        }

        return await q.FirstOrDefaultAsync();