C# 使用LINQ从SQL数据库中的联接表中获取DataGrid项

我的SQL Server Express数据库中有这些表

我的目标是将“UserInfo”表与“RelCU”表连接起来，并将结果显示在wpf数据网格中

我尝试了这些代码，但在运行项目时出错

IQueryable<RelCU> Query =  from u in dbEntities.UserInfoes
                           join m in dbEntities.RelCUs
                           on u.UserID equals m.UserID into temp
                           from j in temp.DefaultIfEmpty()
                           select j;
DataGridRegisteredUsers.ItemsSource = Query;

IQueryable Query=来自dbEntities.UserInfoes中的u
在dbEntities.RelCUs中加入m
u.UserID等于m.UserID到temp
来自临时DefaultIfEmpty（）中的j
选择j；
DataGridRegisteredUsers.ItemsSource=Query；

XAML:

  <DataGrid x:Name="DataGridRegisteredUsers" IsReadOnly="True" AutoGenerateColumns="False" HorizontalContentAlignment="Stretch" Margin="0,0,-1,-1"
                                  FlowDirection="RightToLeft" Opacity="0.9" FontFamily="B Nazanin" FontSize="15">
                            <DataGrid.Columns>
                                <DataGridTextColumn Binding="{Binding Path=UserInfoes.UserID}" IsReadOnly="True"
                                                    Header="ID" />
                                <DataGridTextColumn Binding="{Binding Path=UserInfoes.FirstName}"
                                                    Header="First Name" />
                                <DataGridTextColumn Binding="{Binding Path=UserInfoes.LastName}"
                                                    Header="Last Name" />
                                <DataGridTextColumn Binding="{Binding Path=RelCUs.Score}"
                                                    Header="Score" />
                                <DataGridTextColumn Binding="{Binding Path=RelCUs.Status}"
                                                    Header="Status" />

                            </DataGrid.Columns>
                        </DataGrid>

 <DataGrid x:Name="DataGridRegisteredUsers" IsReadOnly="True" AutoGenerateColumns="False" HorizontalContentAlignment="Stretch" Margin="0,0,-1,-1"
                              FlowDirection="RightToLeft" Opacity="0.9" FontFamily="B Nazanin" FontSize="15">
                        <DataGrid.Columns>
                            <DataGridTextColumn Binding="{Binding Path=ID}" IsReadOnly="True"
                                                Header="ID" />
                            <DataGridTextColumn Binding="{Binding Path=FirstName}"
                                                Header="First Name" />
                            <DataGridTextColumn Binding="{Binding Path=LastName}"
                                                Header="Last Name" />
                            <DataGridTextColumn Binding="{Binding Path=Score}"
                                                Header="Score" />
                            <DataGridTextColumn Binding="{Binding Path=Status}"
                                                Header="Status" />

                        </DataGrid.Columns>
                    </DataGrid>

---

谢谢

您正在使用

LEFT JOIN

，并且

选择j

，因此

j

可以为空：

  IQueryable<RelCU> Query = from u in dbEntities.UserInfoes
                            join m in dbEntities.RelCUs
                            on u.UserID equals m.UserID into temp
                            from j in temp.DefaultIfEmpty()
                            select new
                            {
                                ID=u.UserID, 
                                FirstName=u.FirstName,
                                LastName=u.LastName,
                                Score = j == null? 0 : j.Score,
                                Status = j == null? "" :j.Status
                            };
  DataGridRegisteredUsers.ItemsSource = Query;

IQueryable Query=来自dbEntities.UserInfoes中的u
在dbEntities.RelCUs中加入m
u.UserID等于m.UserID到temp
来自临时DefaultIfEmpty（）中的j
选择新的
{
ID=u.UserID，
FirstName=u.FirstName，
LastName=u.LastName，
分数=j==null？0:j.分数，
状态=j==null？”：j.Status
};
DataGridRegisteredUsers.ItemsSource=Query；

XAML:

  <DataGrid x:Name="DataGridRegisteredUsers" IsReadOnly="True" AutoGenerateColumns="False" HorizontalContentAlignment="Stretch" Margin="0,0,-1,-1"
                                  FlowDirection="RightToLeft" Opacity="0.9" FontFamily="B Nazanin" FontSize="15">
                            <DataGrid.Columns>
                                <DataGridTextColumn Binding="{Binding Path=UserInfoes.UserID}" IsReadOnly="True"
                                                    Header="ID" />
                                <DataGridTextColumn Binding="{Binding Path=UserInfoes.FirstName}"
                                                    Header="First Name" />
                                <DataGridTextColumn Binding="{Binding Path=UserInfoes.LastName}"
                                                    Header="Last Name" />
                                <DataGridTextColumn Binding="{Binding Path=RelCUs.Score}"
                                                    Header="Score" />
                                <DataGridTextColumn Binding="{Binding Path=RelCUs.Status}"
                                                    Header="Status" />

                            </DataGrid.Columns>
                        </DataGrid>

 <DataGrid x:Name="DataGridRegisteredUsers" IsReadOnly="True" AutoGenerateColumns="False" HorizontalContentAlignment="Stretch" Margin="0,0,-1,-1"
                              FlowDirection="RightToLeft" Opacity="0.9" FontFamily="B Nazanin" FontSize="15">
                        <DataGrid.Columns>
                            <DataGridTextColumn Binding="{Binding Path=ID}" IsReadOnly="True"
                                                Header="ID" />
                            <DataGridTextColumn Binding="{Binding Path=FirstName}"
                                                Header="First Name" />
                            <DataGridTextColumn Binding="{Binding Path=LastName}"
                                                Header="Last Name" />
                            <DataGridTextColumn Binding="{Binding Path=Score}"
                                                Header="Score" />
                            <DataGridTextColumn Binding="{Binding Path=Status}"
                                                Header="Status" />

                        </DataGrid.Columns>
                    </DataGrid>

显示了什么错误？出现了什么错误？您正在使用

左连接

，并且

选择j

，因此

j

可以

null

@EdiG.&visgu minhas:我收到了此错误：EntityFramework.dll中发生了类型为“System.NotSupportedException”的未处理异常