Question

我在尝试访问以下方法时遇到错误，

public ZipCode GetByZip(string zip)
    {
        using (GeoLibDbContext entityContext = new GeoLibDbContext())
        {
            return entityContext.ZipCodeSet.Include(e => e.StateId).FirstOrDefault(e => e.Zip == zip);
        }
    }

下面是POCO和db上下文类，

public class State
{
    public int StateId { get; set; }
    public string Name { get; set; }
}

 public class ZipCode 
{
    public int ZipCodeId { get; set; }
    public string City { get; set; }
    public int StateId { get; set; }
    public string Zip { get; set; }
    public string County { get; set; }
    public State State { get; set; }
}

public class HelloLibDbContext : DbContext
{
    public HelloLibDbContext()
        : base("name=HelloLibDbContext")
    {
        Database.SetInitializer<HelloLibDbContext>(null);
    }

    public DbSet<ZipCode> ZipCodeSet { get; set; }
    public DbSet<State> StateSet { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();

        modelBuilder.Entity<ZipCode>().HasKey<int>(e => e.ZipCodeId)
            .HasRequired(e => e.State).WithMany().HasForeignKey(e => e.StateId);

        modelBuilder.Entity<State>().HasKey<int>(e => e.StateId);
    }

}

如果我删除了“.Include（e =＆gt; e.StateId）”，那么我得到任何错误，但同时“State”属性为null，它在“ZipCode”类中定义。

可能是什么原因？请建议!!!

Answer 1

您应该加入State。不是StateId

public ZipCode GetByZip(string zip)
{
    using (GeoLibDbContext entityContext = new GeoLibDbContext())
    {
        return entityContext.ZipCodeSet.Include(e => e.State).FirstOrDefault(e => e.Zip == zip);
    }
}

包括使用导航属性，在您的情况下导航属性为State。

EntityType不声明名为“StateId”的导航属性

1 个答案: