I am trying to provide an API to insert a parent object with children objects. For testing, I modified a little from the phonebook example, but it always throws out System.NullReferenceException: Object reference not set to an instance of an object.
Here is my code:
public async Task<PhoneInPersonListDto> AddPhone(AddPhoneInput input)
{
var person = new Person();
person.Name = "x";
person.Surname = "y";
var phone = ObjectMapper.Map<Phone>(input);
person.Phones.Add(phone);
var personId = await _personRepository.InsertAndGetIdAsync(person);
return ObjectMapper.Map<PhoneInPersonListDto>(phone);
}
Can you advise what I missed?
Thanks,
3 Answer(s)
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0
Hi,
You need to create an empty list for Phones of person before adding an item to it. You can do it in the constructor of your Person entity.
Thanks.
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0
Got it. Because the Phone is defined in Person as virtual ICollection<Phone>, it is not initiated along with "new Person()". I modified my code as following (adding 2 lines with comment):
public async Task<PhoneInPersonListDto> AddPhone(AddPhoneInput input) { var person = new Person(); person.Phones = new List<Phone>(); // concrete ICollection<Phone> person.Name = "x"; person.Surname = "y";
var phone = ObjectMapper.Map<Phone>(input); person.Phones.Add(phone);
var personId = await _personRepository.InsertAndGetIdAsync(person); var phoneId = phone.Id; // Cannot get this if using InsertAsync(person).
return ObjectMapper.Map<PhoneInPersonListDto>(phone); }
It works as expected. Thank you! :)
BTW, do you think the "new List<T>(); " is the best way to initiate ICollection<T>?
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0
Hi,
BTW, do you think the "new List<T>(); " is the best way to initiate ICollection<T>?
I personally use it like that but I don't know if it is the best way or not :)
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