Find differences between two lists in EF Core

Question

I have two lists.

Client List: one of them receive from user (client)

Server List: one of them get from database.

I want to do 3 work on this lists.

One: Add ( if data not exists in server List and exist in the client List )

Two: Remove data ( if exist in the server List and not exist in the client List )

Three: Update ( if data exist in server List and client Server and data has Changed )

This is my model:

public class CategoryPropertyDto
{
    public Guid? Id { get; set; }
    public Guid CategoryId { get; set; }
    public string PropName { get; set; }
    public CategoryPropertyType CategoryPropertyType { get; set; }
}

the client send me the list of this model CategoryPropertyDto .

Now I write this code for adding data:

var currentValue = getAllPropByCategory.Result.Select(x => new CategoryPropertyDto
            {
                CategoryId = x.CategoryId,
                CategoryPropertyType = x.CategoryPropertyType.CategoryPropertyType,
                Id = x.Id,
                PropName = x.PropName
            }).ToList();
            /// Add New Property
            var newProp = request.CategoryPropertyDtos.Where(x => x.Id == null).ToList();
            List<CategoryProperty> CategoryProperty = new List<CategoryProperty>();
            if (newProp.Count() > 0)
            {
                foreach (var item in newProp)
                {
                    CategoryProperty.Add(new CategoryProperty(item.PropName, item.CategoryPropertyType, item.CategoryId));
                }
                await unitOfWork.CategoryRepository.CategoryPropertyRepository.AddBulkCategoryProperty(CategoryProperty, cancellationToken);
            }

and its worked well.

Now I want to find items for remove (exist in the server List but not exist in the clientList)

 var removeValue = currentValue.Except(request.CategoryPropertyDtos).ToList();

but it did not work and return all currentValue and I don't know how can I find the items for update.

How can I solve this problem?

Answer 1

var removeValue = currentValue.Except(request.CategoryPropertyDtos).ToList();

This line does not work because in this case Except method compare References, not Values and obviously currentValue items have different references than client items.

solution: You have to use Id in all cases (add, delete, update) as you already did for Add case. So for example to find items to delete:

var ItemIdsToDelete = currentValue.Select(p => p.Id).Except(request.CategoryPropertyDtos.Select(p => p.Id)).ToList();

and delete items by id using method like this:

await unitOfWork.CategoryRepository.CategoryPropertyRepository.DeleteBulkCategoryPropertyById(ItemIdsToDelete, cancellationToken);

and you can do similar thing to find items that their ids exist in both client and server lists and update them.