从一对多关系中删除子对象

Question

(Code has been simplified)

Background description:

I have a parent class:

namespace Project_Name.Models
{
    public class ParentRecord
    {
        [Key, DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public Guid Id { get; set; }

        public virtual ICollection<ChildDetail> ChildDetails { get; set; }
    }
}

and a child class:

namespace Project_Name.Models
{
    public class ChildDetail
    {
        [Key, DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public Guid Id { get; set; }

        public string Value { get; set; }

        public Guid ParentRecord_Id { get; set; }

        [ForeignKey("ParentRecord_Id")]
        public ParentRecord ParentRecord { get; set; }
    }
}

I also have ViewModels with the names <modelName>ViewModel and almost exact structure, except with no Data Annotations and virtual ICollection is just a List

Together they form a One-to-Many relationship. ParentRecord can have many ChildDetails , and ChildDetail must be associated with a ParentRecord .

The T-SQL table structure comes out like this:

dbo.ParentRecord
+-----------+
|    Id     |
+-----------+
| <cr_guid> |
+-----------+

dbo.ChildDetail
+-----------+-----------+-----------------+
|    Id     |   Value   | ParentRecord_Id |
+-----------+-----------+-----------------+
| <cd_guid> | Some Text | <cr_guid>       |
+-----------+-----------+-----------------+

---

My problem:

I need to be able to update, add, and/or remove these child objects based on what my ViewModel has. Whatever it has, I want to be the end result.

For example, I start off by having 3 ChildDetails related to the ParentRecord , then in my View I update the 1st ChildDetail , remove the 2nd (or leave the value blank), and leave the 3rd one alone.

I hope my end result to be that this ParentRecord is left with two ChildDetails , the 1st and 3rd, with the 1st one being updated.

---

What I've done so far:

I'm able to add and update ChildDetails doing this, but it doesn't handle any deletion:

// ... code related to UnrelatedGranParent model
ParentRecord parentRecord = context.ParentRecords.FirstOrDefault(x => 
   x.Id == UnrelatedGrandParentViewModel.ParentViewModel.Id)
// ... code regarding ParentRecord's other not-shown-here properties

// Add or update each Child Detail from the View Model
foreach (var childDetailViewModel in ParentRecordViewModel
    .ChildDetailViewModels
    .Where(x => !x.Value.IsNullOrWhiteSpace()))
{
    // Map the Child Detail View Model to a Model
    var childDetail =
        Mapper.Map<ChildDetail>(childDetailViewModel);
    // Set the ParentRecord_Id property, since that doesn't get mapped
    childDetail.ParentRecord_Id = parentRecord.Id;
    // Add or update each Child Detail
    context.ChildDetails.AddOrUpdate(childDetail);
}

context.ParentRecord.AddOrUpdate(parentRecord);
context.SaveChanges();

So I want parentRecord.ChildDetails set to whatever just got passed in, assuming it's not null or whitespace.
So I have to delete everything else.

I've tried looping through each existing ChildDetail and using either .Remove() on them or setting their context.Entry(childDetail).State = EntityState.Deleted or EntityState.Detached then as I loop through the values from the view model setting them to either EntityState.Added or EntityState.Modified , but keeps throwing errors either when I'm changing the state or saving changes depending.

I can also move the .Where(x => !x.Value.IsNullOrWhiteSpace()) into the foreach loop to be:

// map the childDetail
if (childDetail.Value.IsNullOrWhiteSpace())
{
    context.Entry(childDetail).State = EntityState.Deleted;
    continue;
}
context.ChildDetails.AddOrUpdate(childDetail);

But this doesn't account for those simply not passed in, and I don't know if it's a good practice to directly set EntityStates.

Answer 1

Thanks to DevilSuichiro's comment I was able to come to this easy solution where I simply check if each ChildDetail from the context exists in the ViewModel's list of ChildDetails , and if it doesn't: delete it!

// Add or update each Child Detail from the View Model
foreach (var childDetailViewModel in callDetailsViewModel.ParentRecordViewModel
    .ChildDetailViewModels)
{
    // Map the Child Detail View Model to a Model
    var childDetail =
        Mapper.Map<ChildDetail>(childDetailViewModel);
    // Set the ParentRecord_Id property, since that doesn't get mapped
    childDetail.ParentRecord_Id = parentRecord.Id;
    // Delete those that are null or whitespace
    if (childDetail.Value.IsNullOrWhiteSpace())
    {
        context.Entry(childDetail).State = EntityState.Deleted;
        continue;
    }

    // Add or update each Child Detail
    context.ChildDetails.AddOrUpdate(childDetail);
}

// For each contextChildDetail in the context, where they have matching Parent Record Id...
foreach (var contextChildDetail in context.ChildDetail.Where(x => x.ParentRecord_Id == parentRecord.Id))
{
    // ... and if we can't find it in the ViewModel list, then delete it
    if (callDetailsViewModel.ParentRecordViewModel.ChildDetailViewModels.FirstOrDefault(
            x => x.Id == contextChildDetail.Id) == null)
    {
        context.ChildDetail.Remove(contextChildDetail);
    }
}