EF用导航属性遍历从表时，删除主表出错

var entitys= Repository.Table.Where(a => ids.Contains(a.UUID)).ToList();
 entitys.ForEach(a =>
 {
 　　//foreach (var deductionitem in a.Deductionitems){} //取出来就删除不了了

　　var items=a.Deductionitems

　　DoDelete(a);
 });

DeductionItems和主表配了级联删除，代码执行时会抛The relationship could not be changed because one or more of the foreign-key properties is non-nullable

场景为：删除主表时，在其对应的子表集合中，从子表通过导航属性去更新另外一个表的某个合计字段

解决方法：

遍历子表后，EF无法分辨该记录是否要保留。所以需要手动删除从表，不能再依赖级联删除

附上主表实体部分字段

public class MaterialSupplierPayApply : BaseSupplierPayApply
    {
        public MaterialSupplierPayApply() { }

        public MaterialSupplierPayApply(Currency currency, decimal exchangeRate, MaterialSupplier supplier) 
            : base(currency, exchangeRate, supplier)
        {

        }

        public override string SysBillTypeCode => FuncCodeConst.Scm.MATERIALSUPPLIERPAYAPPLY;

        private List<MaterialSupplierPayDeductionItem> _deductionItems;
        /// <summary>
        /// 应付扣款明细
        /// </summary>
        public virtual List<MaterialSupplierPayDeductionItem> DeductionItems
        {
            get => _deductionItems ?? (_deductionItems = new List<MaterialSupplierPayDeductionItem>());
            set => _deductionItems = value;
        }

    }

以下为子表实体

/// <summary>
/// 应付扣款明细
/// </summary>
public class MaterialSupplierPayDeductionItem:BaseEntityLog

    {
        public MaterialSupplierPayDeductionItem() { }

        public MaterialSupplierPayDeductionItem(MaterialSupplierPayableDeduction materialSupplierPayableDeduction,Guid billId)
        {
            BillId = billId;
            materialSupplierPayableDeduction.WriteOffStatus = WriteOffStatus.WriteOffing;
            MaterialSupplierPayableDeduction = materialSupplierPayableDeduction;
        }

        /// <summary>
        /// 付款申请
        /// </summary>
        public Guid BillId { get; set; }

        /// <summary>
        /// 材料商应付扣款Id
        /// </summary>
        public Guid MaterialSupplierPayableDeductionId { get; set; }

        /// <summary>
        /// 备注
        /// </summary>
        public string Description { get; set; }

        #region 导航属性

        /// <summary>
        /// 材料商付款申请
        /// </summary>
        public virtual MaterialSupplierPayApply MaterialSupplierPayApply { get; set; }

        /// <summary>
        /// 材料商应付扣款
        /// </summary>
        public virtual MaterialSupplierPayableDeduction MaterialSupplierPayableDeduction { get; set; }

        #endregion
    }