Not understanding why I must instantiate the class?

Question

i have an entitity:

public virtual int RecommendedUserId { get; set; }
public virtual string Firstname { get; set; }
public virtual string Surname { get; set; }
public virtual string Email { get; set; }
public virtual string JobTitle { get; set; }
public virtual DateTime? DateAndTimeProcessed { get; set; }
public virtual DateTime? DateAndTimeRecommended { get; set; }
public virtual string ReasonForRejection { get; set; }

//  User also an entity and has property UserId
public virtual User RecommendedByUser { get; set; }
public virtual User AssignedToUser { get; set; }

in my controller i have:

   Entities.RecommendedUser user = new RecommendedUser();
   user.Firstname = model.Firstname;
   user.Surname = model.Surname;
   user.Email = model.Email;
   user.JobTitle = model.JobTitle;

   // why am i getting the Object reference not set to 
   // an instance of an object error??
   user.RecommendedByUser.UserId = CurrentUser.UserId;

if I instantiate RecommendedUser dont i instantiate User within RecommendedUser as well??

No, each object must be instantiated. Or, the default constructor of RecommendedUser() must create a new RecommendedByUser() somehow. — mtsiakiris, Apr 26 '13 at 08:37

score 3 · Accepted Answer · answered Apr 26 '13 at 08:38

3

You are not instantiating the RecommendedByUser of user; you are only instatiating the user.

   user.Firstname = model.Firstname;
   user.Surname = model.Surname;
   user.Email = model.Email;
   user.JobTitle = model.JobTitle;
   user.RecommendedByUser = new RecommendedUser(); // or whatever the exact type is, maybe just User
   user.RecommendedByUser.UserId = CurrentUser.UserId;

answered Apr 26 '13 at 08:38

daryal

14,643
4
38
54

`RecommendedByUser` is of type `User`. – Corak Apr 26 '13 at 08:39
1

I think he knows how to instantiate it, the question is why does he need to – Sayse Apr 26 '13 at 08:40
@Corak but RecommendedUser has a property called RecommendedByUser which is not being instantiated. – daryal Apr 26 '13 at 08:40
@daryal - `RecommendedUser` has a property called `RecommendedByUser` which is of type `User`. (`public virtual User RecommendedByUser { get; set; }`) – Corak Apr 26 '13 at 08:42
@Corak the same as what I have written? – daryal Apr 26 '13 at 08:43
@daryal - not exactly. Your `user.RecommendedByUser = new RecommendedUser();` should be `user.RecommendedByUser = new User();`. – Corak Apr 26 '13 at 08:46

score 2 · Answer 2 · answered Apr 26 '13 at 08:41

Value types are initialized with the class. However child objects can be NULL as they are reference types. Those objects need to be initialized before they can be assigned to a property.

I assume you are using a technology like Entity Framework. Frameworks like this allow you to prefetch these objects so they will be fetched (and initialized) when you get the entity from your datasource. However when creating new objects you will need to create them yourself.

score 0 · Answer 3 · edited May 23 '17 at 12:04

0

In the case of EntityFramework, there is the Lazy loading feature. In your specific case that does not apply because your object is not tracked by the EF context. Lazy loading (and then automatic instanciation) is only active if your object is tracked.

This thread could be instructive.

edited May 23 '17 at 12:04

Community

1
1

answered Apr 26 '13 at 08:47

Askolein

3,250
3
28
40

score 0 · Answer 4 · answered Apr 26 '13 at 08:49

0

You should always first check for null values Like:

if(user.Firstname != null)
{
  user.Firstname = model.Firstname;
}

To avoid nullpointer exceptions

answered Apr 26 '13 at 08:49

Paul.K

3
1
3

In your example, it is useless. More like: `if(user != null && model != null) user.FirstName = model.FirstName;` – Askolein Apr 26 '13 at 09:58

Not understanding why I must instantiate the class?

4 Answers4