I am Using AutoMapper and when i update a single value it makes the rest of them null

Question

I am using AutoMapper and this is my code to update the details of an existing customer but when I update one field the rest of the fields get nulled.

public async Task<ResponseModel> Update(CustomerDTO customer, int id)
{
        ResponseModel responseModel = new ResponseModel();

        try
        {
            Customer? existingCustomer = await _dbContext.FindAsync<Customer>(id);

            if (existingCustomer == null)
            {
                return new ResponseModel()
                {
                    IsSuccess = false,
                    Message = $"Customer doesn't exist!"
                };
            }

            _mapper.Map(customer, existingCustomer);

            if (await _dbContext.SaveChangesAsync() > 0)
            {
                responseModel.Message = "Customer Updated Successfully";
                responseModel.IsSuccess = true;
            }
        }
        catch (Exception ex)
        {
            responseModel.IsSuccess = false;
            responseModel.Message = $"Error:{ex.Message}";
        }

        return responseModel;
}

Here's the mapper profile:

using AutoMapper;
using static MGApi.Services.CustomerService;

namespace MGApi.Models
{
    public class CustomerProfile : Profile
    {
        public CustomerProfile()
        {
            CreateMap<CustomerDTO, Customer>();
        }
    }
}

I tried adding using ForAllOtherMembers but it is deprecated. I'm not sure how to solve this.

Here is the Customer Model:

using System.ComponentModel.DataAnnotations;

namespace MGApi.Models
{
    public class Customer
    {
        [Key]
        public int Id { get; set; }

        [Required]
        [StringLength(50)]
        [RegularExpression(@"^\d{10}$", ErrorMessage = "Invalid phone number")]

        public string? PhoneNumber { get; set; }

        [Required]
        [StringLength(50)]
        public string? Name { get; set; }

        [StringLength(100)]
        [EmailAddress]
        public string? Email { get; set; }

        [StringLength(10)]
        public string? Gender { get; set; }

        [DataType(DataType.Date)]
        public DateTime DateOfBirth { get; set; }
        public ICollection<CustomerData>? CustomerData { get; set; }

    }
}

Now below we have the CustomerData Model which has a foreign key based on the primary key of the Customer Model:

using System.ComponentModel.DataAnnotations;

namespace MGApi.Models
{
    public class CustomerData
    {
        [Key]
        public int Id { get; set; }
        public int CustomerId { get; set; }

        public double Sugar { get; set; }

        public double BP { get; set; }

        public double Height { get; set; }

        public double Weight { get; set; }

        public DateTime Timestamp { get; set; } = TimeZoneInfo.ConvertTimeFromUtc(DateTime.UtcNow, TimeZoneInfo.FindSystemTimeZoneById("India Standard Time"));

        public Customer? Customer { get; set; }
    }
}

Answer 1

I think it is because of your nullable fields in Customer and CustomerDtoand bunch of fields of CustomerDto instance are null. I have two solutions for your problem: First, use JsonPatch for partial updating.

Second, prevent mapping null values from source to destination by changing you mapping profile as follows:

CreateMap<CustomerDTO, Customer>().ForAllMembers(options => options.Condition((src, dest, srcMember) => srcMember != null));