Question

        _context.Homestays   
                .Include(x => x.CreatedUser)
                .Include(x => x.UpdatedUser)
                .Include(x => x.HomestayEvaluations)
                .Include(x => x.HomestayContracts)
                .Include(x => x.HomestayPoliceChecks)
                .Include(x => x.HomestayHouseHolds)
                .AsNoTracking()
                .Select(x => new Homestay()
                {
                    HomestayId = x.HomestayId,
                    HomestayFamily = ConstValue.GetHomestayFamilyName(x),
                    Address = x.Address,
                    Score = x.HomestayEvaluations.Any(x1 => x1.IsEvaluationActive) ? x.HomestayEvaluations.LastOrDefault(x1 => x1.IsEvaluationActive).GetScore() : 0,
                    Contract = x.HomestayContracts.Any(x1 => x1.IsContractActive) ? x.HomestayContracts.LastOrDefault(x1 => x1.IsContractActive).ContractDate : null,
                    Students = x.Students,
                    HouseHolders = x.HomestayHouseHolds.Count(x1 => x1.IsHouseHoldActive),
                    PoliceCheck = x.HomestayPoliceChecks.Any(x1 => x1.IsPoliceCheckActive) ? x.HomestayPoliceChecks.LastOrDefault(x1 => x1.IsPoliceCheckActive).PoliceCheckDate : null,
                    Language = x.Language,
                    Room = x.Room,
                    IsActive = x.IsActive,
                    CreatedDate = x.CreatedDate,
                    CreatedUserName = ConstValue.GetUserName(x.CreatedUser),
                    UpdatedDate = x.UpdatedDate,
                    UpdatedUserName = ConstValue.GetUserName(x.UpdatedUser)
                })
                .OrderByDescending(x => x.HomestayId);

您好，我想知道如何更好地更改我的选择查询？

此代码如下所示，看起来很乱。首先执行任何，如果是真的，请获取最后一个。但是还有更短的代码吗？

Contract = x.HomestayContracts.Any（x1 =＆gt; x1.IsContractActive）？ x.HomestayContracts.LastOrDefault（x1 =＆gt; x1.IsContractActive）.ContractDate：null

我试过没有任何（），如果没有数据，它会将错误视为空对象。

请帮帮我。

谢谢：）

Answer 1

使用此

Contract = x.HomestayContracts.LastOrDefault(x1 => x1.IsContractActive)?.ContractDate ?? null

此外，您可以在上下文配置中禁用此查询的延迟加载

context.Configuration.LazyLoadingEnabled = false;

通过这种方式，您可以消除Include方法，导致语句缩短但性能不佳。使用存储过程来提高性能。 Stored Procedure in Entity Framework

在EF Core中选择性能问题

1 个答案: