Question

我正在学习EF Code First，但我遇到了问题。我有主要和详细的抽象类，在数据绑定到UI控件期间，我收到一个异常。

在在线课程的WPF主/详细信息表格中，我为学生提供了一个DataGrid（详细信息）。当我尝试向DataGrid添加一行时抛出此异常

无法创建NameSpace.student的实例，因为它是一个抽象类。

那么如何将Students集合映射为OnlineStudents在onlineCourse和OfflineStudents在offlineCourse中？

public abstract class Course
    {
        public int Id { get; set; }
        public string Description{ get; set; }
        public System.DateTime StartDate { get; set; }

        public virtual System.Collections.ObjectModel.ObservableCollection<Student> Students { get; set; }
    }

    public abstract class Student
    {
        public int Id { get; set; }
        public string Name { get; set; }

        public int CourseID { get; set; }
        public virtual Course course { get; set; }
    }

    public class OnlineCouse : Course
    {
        public string URI { get; set; }
    }

    public class OnlineStudent : Student
    {
        public string Email { get; set; }
    }

    class InstContext : DbContext
    {

        public InstContext()
            : base()
        {

        }

        public DbSet<Course> Course{ get; set; }
        public DbSet<Student> Student{ get; set; }

        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            Database.SetInitializer<InstContext>(new DropCreateDatabaseIfModelChanges<InstContext>());



            modelBuilder.Entity<OnlineCouse>().Map(m =>
            {
                m.MapInheritedProperties();
                m.ToTable("OnlineCourse");
            });

            modelBuilder.Entity<OnlineStudent>().Map(m =>
            {
                m.MapInheritedProperties();
                m.ToTable("OnlineStudent");
            });
        }
    }

以下是Xaml

<Window.Resources>
    <CollectionViewSource x:Key="onlineCourseViewSource" d:DesignSource="{d:DesignInstance {x:Type XData:OnlineCourse}, CreateList=True}"/>
    <CollectionViewSource x:Key="onlineCourseStudentsViewSource" Source="{Binding Students, Source={StaticResource gSVoucherViewSource}}"/>
</Window.Resources>
<Grid DataContext="{StaticResource onlineCourseViewSource}">
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="Auto"/>
            <ColumnDefinition Width="Auto"/>
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
        <RowDefinition Height="Auto"/>
        <RowDefinition Height="Auto"/>
    </Grid.RowDefinitions>
    <Label Content="Id:"  Grid.Row="0" Grid.Column="0" HorizontalAlignment="Left" Margin="3" VerticalAlignment="Center"/>
    <TextBox x:Name="idTextBox"  Grid.Row="0" Grid.Column="1" HorizontalAlignment="Left" Height="23" Margin="3" Text="{Binding Id, Mode=TwoWay, NotifyOnValidationError=true, ValidatesOnExceptions=true}" VerticalAlignment="Center" Width="120"/>
    <Label Content="Email:"  Grid.Row="1" Grid.Column="0" HorizontalAlignment="Left" Margin="3" VerticalAlignment="Center"/>
    <TextBox x:Name="EmailTextBox"  Grid.Row="1" Grid.Column="1" HorizontalAlignment="Left" Height="23" Margin="3" Text="{Binding Email, Mode=TwoWay, NotifyOnValidationError=true, ValidatesOnExceptions=true}" VerticalAlignment="Center" Width="120"/>

    <DataGrid x:Name="studentsDataGrid"   Grid.Row="2" Grid.Column="0" ItemsSource="{Binding Source={StaticResource onlineCourseStudentsViewSource}}" Grid.ColumnSpan="2"  AutoGenerateColumns="False" EnableRowVirtualization="True"   RowDetailsVisibilityMode="VisibleWhenSelected">
        <DataGrid.Columns>
            <DataGridTextColumn x:Name="idColumn" Binding="{Binding Id}" Header="Id" Width="SizeToHeader"/>
            <DataGridTextColumn x:Name="nameColumn" Binding="{Binding Name}" Header="In Area" IsReadOnly="True" Width="SizeToHeader"/>         
        </DataGrid.Columns>
    </DataGrid>
</Grid>

问题是：如果我有一个抽象的主类，它有一个抽象的子类集合，如何在派生的主类中重写它以获得派生的子集合？

Entity Framework 6.0继承集合映射

0 个答案: