在没有外键的情况下从实体框架中获取子对象

Question

我负责视图/视图模型而不是项目模型。模型设置如下：

[Table("Activity")]
public class Activity
{
    [Key]
    public int ActivityId { get; set; }

    public string OtherProperties { get; set; }
}

[Table("Class1")]
public class Class1
{
    [Key]
    public int Class1Id { get; set; }

    public string Name { get; set; }

    public ObservableCollection<Activity> Activities { get; set; }
}

[Table("Class2")]
public class Class2
{
    [Key]
    public int Class2Id { get; set; }

    public string Name { get; set; }

    public ObservableCollection<Activity> Activities { get; set; }
}

编辑

我试图通过对Activity类进行调用来填充DataGrid。此Grid在另一个类中有一个“Name”属性列。如何通过ViewModel从Activity类的两个类中获取“Name”列的列表（或Class对象本身的列表）？

WPF

<DataGrid ItemsSource="{Binding Activities}"
          Grid.ColumnSpan="3"
          Grid.Row="1"
          HorizontalAlignment="Stretch"
          AutoGenerateColumns="False"
          >
    <DataGrid.Columns>
        <DataGridTemplateColumn Header="Complete">
            <DataGridTemplateColumn.CellTemplate>
                <DataTemplate>
                    <Button Command="{Binding Path=DataContext.CompleteTaskCommand, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type local:BasePage}}}"
                            CommandParameter="{Binding ActivityId}"
                            Content="{StaticResource FontAwesomeCheckIcon}"
                            Foreground="Green"
                            Grid.Column="0"
                            HorizontalAlignment="Center"
                            Style="{StaticResource FontAwesomeIconButton}"
                            VerticalAlignment="Center"
                            />
                </DataTemplate>
            </DataGridTemplateColumn.CellTemplate>
        </DataGridTemplateColumn>
        <DataGridTextColumn Binding="{Binding DueDate, StringFormat=MM/dd/yyyy, Converter={local:UtcToLocalDateTimeValueConverter}}" Header="Due Date"/>
        <DataGridTextColumn Binding="{Binding IsComplete, Converter={local:BooleanToStringParameterValueConverter}, ConverterParameter=CompletedOpen}" Header="Status"/>
        <DataGridTextColumn Binding="{Binding Subject}" Header="Subject"/>
        <DataGridTextColumn Binding="{Binding Name}" Header="Name"/> ??????????
    </DataGrid.Columns>
</DataGrid>

视图模型

Activities= DB.GetAll<Activity>().Where(x => x.IsDeleted == false && x.AssignedTo == user);

GetAll方法

public IEnumerable<T> GetAll<T>() where T : EcoDevBase, new()
{
    // if no items, returns an empty list
    IEnumerable<T> entityList = _Context.Set<T>().ToList();
    return entityList;
}

Answer 1

我不确定你在一开始就设置了什么，但是有很多方法可以使用LINQ来实现你的需求。例如：

var desiredActivity = Activity;
var class1Names = DbContext.Class1.Where(e => e.Activities.Contains(desiredActivity).Select(e => e.Name)

var class2Names = DbContext.Class2.Where(e => e.Activities.Contains(desiredActivity).Select(e => e.Name)

var listOfNames = new List<string>;

listOfNames.AddRange(class1Names);
listOfNames.AddRange(class2Names);

它可能不是最佳解决方案，但您没有提供有关您希望如何处理业务对象的大量信息。

编辑：

引用您的ViewModel，您有所需活动的列表，现在您想知道哪个Class对象包含此活动，然后您可以执行以下操作：

var listOfNames = new List<string>;
foreach (var activity in Activities)
{
 var class1Names = DbContext.Class1.Where(e => e.Activities.Contains(activity).Select(e => e.Name)

    var class2Names = DbContext.Class2.Where(e => e.Activities.Contains(activity).Select(e => e.Name)

    listOfNames.AddRange(class1Names);
    listOfNames.AddRange(class2Names);
}

现在，您可以通过调用从listOfNames中删除重复项

var fixedListOfNames = new List<string>;
fixedListOfNames.AddRange(listOfNames.Distinct());

如果您想获得对象列表，可以执行以下操作：

 var listOfClasses1 = new List<Class1>;
var listOfClasses2 = new List<Class2>;
    foreach (var activity in Activities)
    {
     var class1Names = DbContext.Class1.Where(e => e.Activities.Contains(activity);

        var class2Names = DbContext.Class2.Where(e => e.Activities.Contains(activity);

        listOfClasses1.AddRange(class1Names);
        listOfClasses2.AddRange(class2Names);
    }

我不确定您的配置，但您可能还需要添加

using System.Data.Entity

和/或.Include(e => e.Activities)您的查询。

最后，如果我是你，我将创建一个业务对象类，其中包含DataGrid所需的属性，以便不对db对象起作用。