Why is my DbContext DbSet null?

问题

I created a new Entity Frameworks Code First app and the DbSet (People) is returning null.

public class Person
{
    public int Id { get; set; }
    public string Name { get; set; }
}

public class Repository : DbContext
{
    public DbSet<Person> People;
}

web.config: connection string

<connectionStrings>
  <add name="Repository"
       connectionString="Data Source=|DataDirectory|Repository.sdf"
       providerName="System.Data.SqlServerCe.4.0"/>
</connectionStrings>

Now when I call

Repository _repo = new Repository()
_repo.People;

_repo.People will be null

What I am missing?

• Microsoft.Data.Entity.Ctp.dll is referenced
• I have tried with and without a database initializer.

回答1:

That's because you define a field of DbSet<Person> on Repository class instead of a property. Once you add a property or change it to be a automatic property,People will start to give you values instead of null. So all you need to do is to change your Repository class to:

public class Repository : DbContext
{
    public DbSet<Person> People { get; set; }
}

回答2:

I just had the same issue. The problem was that I did set these properties as 'internal' while they must have been 'public'. Just in case someone is still searching :)

回答3:

I just had the same issue. The problem was that I did set these properties as 'internal' while they must have been 'public'. Just in case someone is still searching :)

I guess, these properties can be internal/public too, if you use them like this:

public class Repository : DbContext
{
    internal DbSet<Person> People { get; set; }

    public Repository()
    {
        //your code here...
        People = Set<Person>();
    }
}

来源：https://stackoverflow.com/questions/4270794/why-is-my-dbcontext-dbset-null