如何更新多对多关系中的联结表

Question

我要更新中间表中的 schooltypeid，这是我的存储库类。

public async Task UpdateSchoolsAsync(SchoolUpdateVm schoolUpdateVm)
        {

            if (_GpsContext != null)
            {
                var schoolsObj =  _GpsContext.School.FirstOrDefault(x => x.ID == Guid.Parse(schoolUpdateVm.id));
                var schoolTypeObj =  _GpsContext.SchoolsSchoolTypes.FirstOrDefault(x => x.SchoolTypeId == Guid.Parse(schoolUpdateVm.schoolTypeId));



                Schools schools = new Schools();
                {
                    schoolsObj.Name = schoolUpdateVm.name;
                    schoolsObj.Email = schoolUpdateVm.email;
                    schoolsObj.Phone = schoolUpdateVm.phone;
                    schoolsObj.Description = schoolUpdateVm.description;
                     schoolsObj.StateID = Guid.Parse(schoolUpdateVm.stateID);
                    schoolsObj.CountryId = Guid.Parse(schoolUpdateVm.countryId);
                     schoolTypeObj.SchoolTypeId = Guid.Parse(schoolUpdateVm.schoolTypeId); //here i can`t update schoolYype

                }
                _GpsContext.School.Update(schoolsObj);
                await _GpsContext.SaveChangesAsync();
            }
        }

这是我在实体框架中的学校表：

public partial class Schools
{
    public Guid ID { get; set; }
    public string Name { get; set; }

    // Navigations

    public ICollection<SchoolsSchoolType> SchoolsSchoolTypes { get; set; }// this is my junction table

}

这是我的 SchoolsSchoolTypes 表：（这是中间表）

Answer 1

我认为您在问题中的模型不完整。 它缺少“加入”实体。

也就是说，如果您有一个“纯”连接实体，除了键（由外键组成）之外没有其他属性，您应该将该类型添加到“Schools”类的“SchoolsSchoolTypes”集合中。 添加实体的代码应该是这样的：

var schoolsObj =  _GpsContext.School.Include(s => s.SchoolsSchoolTypes ).FirstOrDefault(x => x.ID == Guid.Parse(schoolUpdateVm.id)); //Include types to verify isn't already added
if (schoolsObj == null) throw new Exception("School not found");
if(schoolsObj.SchoolsSchoolTypes.Any(st=>st.SchoolTypeId == schoolUpdateVm.schoolTypeId) throw new Exception("School already has this type");
var schoolTypeObj =  _GpsContext.SchoolsSchoolTypes.FirstOrDefault(x => x.SchoolTypeId == Guid.Parse(schoolUpdateVm.schoolTypeId));
if (schoolsObj == null) throw new Exception("School type not  found");
schoolsObj.SchoolsSchoolTypes.Add(schoolTypeObj);
await _GpsContext.SaveChangesAsync();

如果“加入实体”有额外的属性（我怀疑是这种情况），那么你必须在将它添加到集合之前创建新的加入实体：

var schoolsObj =  _GpsContext.School.Include(s => s.SchoolsSchoolTypes ).FirstOrDefault(x => x.ID == Guid.Parse(schoolUpdateVm.id)); //Include types to verify isn't already added
if (schoolsObj == null) throw new Exception("School not found");
if(schoolsObj.SchoolsSchoolTypes.Any(st=>st.SchoolTypeId == schoolUpdateVm.schoolTypeId) throw new Exception("School already has this type");
var schoolTypeObj =  _GpsContext.SchoolTypes.FirstOrDefault(x => x.SchoolTypeId == Guid.Parse(schoolUpdateVm.schoolTypeId));
if (schoolsObj == null) throw new Exception("School type not  found");
var newSchollType = new SchoolsSchoolTypes()
{
    SchollId = Guid.Parse(schoolUpdateVm.id),
    SchoolTypeId = Guid.Parse(schoolUpdateVm.schoolTypeId),
    OtherProperty = "OtherPropertyValue"
}
schoolsObj.SchoolsSchoolTypes.Add(newSchollType);
await _GpsContext.SaveChangesAsync();