C # Entity Framework with linq returns null reference

Question

I have a problem with entity infrastructure in C #. I have 2 objects, User and UserRole. They are related by the relationship User * → 1 UserRole

Whenever I use this request in a function:

User user = context.User.Where(i => i.id == id).FirstOrDefault(); return user.UserRole.accessLevel; 

The request returns the user, but UserRole is null. The User table has a roleId, which is associated with the UserRole identifier, and the roleId value, if properly debugged, although the UserRole object is null. It's weird like never before ...

I have already made sure that my relationships in the model and database are correct. I have the correct rows added to the database.

EDIT:

Sorry, I should have mentioned that I am using a custom test database controller:

 public class DBController : IUnitOfWork { readonly ObjectContext context; const string ConnectionStringName = "MarketPlaceDBEntities"; public DBController() { var connectionString = ConfigurationManager .ConnectionStrings[ConnectionStringName] .ConnectionString; context = new ObjectContext(connectionString); } public void Commit() { context.SaveChanges(); } public IObjectSet<Category> Category { get { return context.CreateObjectSet<Category>(); } } public IObjectSet<ItemComment> ItemComment { get { return context.CreateObjectSet<ItemComment>(); } } public IObjectSet<ItemRating> ItemRating { get { return context.CreateObjectSet<ItemRating>(); } } public IObjectSet<Item> Item { get { return context.CreateObjectSet<Item>(); } } public IObjectSet<ItemSale> ItemSale { get { return context.CreateObjectSet<ItemSale>(); } } public IObjectSet<ItemScreenshot> ItemScreenshot { get { return context.CreateObjectSet<ItemScreenshot>(); } } public IObjectSet<UserRole> UserRole { get { return context.CreateObjectSet<UserRole>(); } } public IObjectSet<User> User { get { return context.CreateObjectSet<User>(); } } } 

And I perform operations through it. Maybe he should do something with my problem.

 interface IUnitOfWork { IObjectSet<Category> Category { get; } IObjectSet<ItemComment> ItemComment { get; } IObjectSet<ItemRating> ItemRating { get; } IObjectSet<Item> Item { get; } IObjectSet<ItemSale> ItemSale { get; } IObjectSet<ItemScreenshot> ItemScreenshot { get; } IObjectSet<UserRole> UserRole { get; } IObjectSet<User> User { get; } void Commit(); } 

I had it all before it worked, but I don’t know why it went wrong.

EDIT2:

Solved! Thanks RicoSuter.

Enabling lazy loading in the constructor of my db controller solved the problem. I thought it was already included because it was set to true in the database model, but it seems that when you create a new context, you must enable it again manually.

 public DBController() { var connectionString = ConfigurationManager .ConnectionStrings[ConnectionStringName] .ConnectionString; context = new ObjectContext(connectionString); context.ContextOptions.LazyLoadingEnabled = true; } 

Answer 1

try looking forward to loading UserRole (join):

 context.User.Include("UserRole").Where(i => i.id == id).FirstOrDefault(); 

or first enable lazy loading:

 context.ContextOptions.LazyLoadingEnabled = true; context.User.Where(i => i.id == id).FirstOrDefault(); 

otherwise, your database is not related to UserRole ...

Answer 2

You can simply do this:

 UserRole user = context.User.Where(i => i.id == id).Select(i => i.UserRole); return user.accessLevel; 

Edit:

Assuming you already have a relationship between User and UserRole

 User user = context.User.Where(i => i.id == id).FirstOrDefault(); UserRole role = context.UserRole.Where(i => user.Contains(i.id)).FirstOrDefault(); return role.accessLevel; 

Assuming you have no relationship between User and UserRole

 int roleid = Convert.ToInt32(context.User.Where(i => i.id == id).Select(i => i.roleid)); UserRole role = context.UserRole.Where(i => i.id == roleid).FirstOrDefault(); return role.accessLevel; 

Also, if you have a relationship, but can't see UserRole under User , than try to add this to your model.

 public IDisposable User() { YourDataContext context = new YourDataContext(); Type ct = context.User.GetType(); return (IDisposable)(ct); } 

Answer 3

try it

User user = context.User.Where(i => i.id == id).FirstOrDefault(); return user==null?null:user.UserRole.accessLevel;