实体框架 6：删除多个父项的子项

Question

请帮忙。我使用 EntityFramework 6。拥有实体：

public class PowerStation {

        public Guid PowerStationId { get; set; }
        public string Name { get; set; }

        public Guid PowerStationTypeId { get; set; }
        public virtual PowerStationType PowerStationType { get; set; }

        public Guid SubjectId { get; set; }
        public DateTime SubjectTransactionTime { get; set; }
        public virtual Subject Subject { get; set; }

        public Guid ParticipantOremId { get; set; }
        public DateTime ParticipantOremTransactionTime { get; set; }
        public virtual ParticipantOrem ParticipantOrem { get; set; }

        public Guid? DcId { get; set; }
        public DateTime? DcTransactionTime { get; set; }
        public virtual Dc Dc { get; set; }

        public virtual ICollection<Equipment> Equipments { get; set; }
        public virtual ICollection<DcLink> DcLinks { get; set; }   
        public virtual ICollection<DcPowerStationProposal> DcPowerStationProposals { get; set; }
}

我尝试删除此实体，但出现异常：

操作失败：无法更改关系，因为 一个或多个外键属性不可为空。当一个 对关系进行更改，相关的外键属性是 设置为空值。如果外键不支持空值， 必须定义一个新的关系，外键属性必须是 分配了另一个非空值，或者不相关的对象必须是 已删除。

我可以试试这个：

entity = db.PowerStations
                    .Include(x => x.Equipments)
                    .Include(x => x.DcLinks)
                    .Include(x => x.DcPowerStationProposals)
                    .FirstOrDefault(x => x.PowerStationId == entity.PowerStationId && x.TransactionTime == entity.TransactionTime);


var station = db.ParticipantOrems.FirstOrDefault(x => x.ParticipantOremId == entity.ParticipantOremId
                && x.TransactionTime == entity.ParticipantOremTransactionTime);
                station.PowerStations.Remove(entity);

var subject = db.Subjects.FirstOrDefault(x => x.SubjectId == entity.SubjectId
                && x.TransactionTime == entity.SubjectTransactionTime);
                subject.PowerStations.Remove(entity);

var dc = db.Dcs.FirstOrDefault(x => x.DcId == entity.DcId
                && x.TransactionTime == entity.DcTransactionTime);
                dc.PowerStations.Remove(entity);

var type = db.PowerStationTypes.FirstOrDefault(x => x.PowerStationTypeId == entity.PowerStationTypeId);
                type.PowerStations.Remove(entity);

db.Equipments.Local.Where(x => x.PowerStation == null).ToList().ForEach(r => Equipments.Remove(r));
db.DcLinks.Local.Where(x => x.PowerStation == null).ToList().ForEach(r => DcLinks.Remove(r));
db.PowerStationProposals.Where(x => x.PowerStation == null).ToList().ForEach(r => DcPowerStationProposals.Remove(r));

Answer 1

如果你想删除整个 PowerStation，你应该删除迁移并重新更新它