SQL Server CE中的每个表是否必须具有主键？

Question

I am creating a simple windows phone 8 application. To store data locally I am using Microsoft's ORM LINQ TO SQL. I assume that it uses SQL Server CE the native database provided by Microsoft. I have defined a table that stores name of the state and its capital.

[Table]
public class State : INotifyPropertyChanged, INotifyPropertyChanging
{
    private string _name;

    public State(string name, string capital)
    {
        this.Name = name;
        this.Capital = capital;
    }

    [Column]
    public string Name
    {
        get
        {
            return _name;
        }
        set
        {
            if (_name != value)
            {
                NotifyPropertyChanging("Name");
                _name = value;
                NotifyPropertyChanged("Name");
            }
        }
    }

    private string _capital;

    [Column]
    public string Capital
    {
        get
        {
            return _capital;
        }
        set
        {
            if (_capital != value)
            {
                NotifyPropertyChanging("Capital");
                _capital = value;
                NotifyPropertyChanged("Capital");
            }
        }
    }


    #region INotifyPropertyChanged Members

    public event PropertyChangedEventHandler PropertyChanged;

    // Used to notify the page that a data context property changed
    private void NotifyPropertyChanged(string propertyName)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }

    #endregion

    #region INotifyPropertyChanging Members

    public event PropertyChangingEventHandler PropertyChanging;

    // Used to notify the data context that a data context property is about to change
    private void NotifyPropertyChanging(string propertyName)
    {
        if (PropertyChanging != null)
        {
            PropertyChanging(this, new PropertyChangingEventArgs(propertyName));
        }
    }

    #endregion
}

I have defined the DataBase Context class as well.

public class DbDataContext : DataContext
{
    // Specify the connection string as a static, used in main page and app.xaml.
    public static string DBConnectionString = "Data Source=isostore:/ToDo.sdf";
    // Pass the connection string to the base class.
    public DbDataContext(string connectionString): base(connectionString)
    { 

    }
    // Specify a single table for the to-do items.
    public Table<State> State_table;
}

Now when I try to insert one row in the Constructor of the MainPage class, It throws an exception saying "System.InvalidOperationException".

public MainPage()
    {

        InitializeComponent();
        State temp = new State("Maharashtra", "Mumbai");
        dbobj = new DbDataContext(DbDataContext.DBConnectionString);
        dbobj.State_table.InsertOnSubmit(temp); //This where it generates an exception
        dbobj.SubmitChanges();
    }

But when I Redefine the Property "Name" in my class "State" as

[Column(IsPrimaryKey = true )]
public string Name

Then it doesnt throw the exception. Can anyone tell me why this is happnening?

Thanks !

Answer 1

Yes each table is required to have a primary Key so that each row can be uniquely identified.

It's also recommended to add a Version column, which dramatically speeds up the performance of the db:

[Column(IsVersion = true)]
#pragma warning disable 169
private Binary version;