<DataGrid Name="gridUsers" AutoGenerateColumns="False" SelectedIndex="0" IsReadOnly="True" SelectionMode="Single" CanUserSortColumns="True" SelectionChanged="GridUsersSelectionChanged">
            <DataGrid.Columns>
                <DataGridTextColumn Header="Фамилия" Binding="{Binding Path=Surname}" />
                <DataGridTextColumn Header="Роль" Binding="{Binding Path=Role.Name, Mode=OneWay}" />
            </DataGrid.Columns>
</DataGrid>

<Grid Margin="10" Name="gridUser" >
        <Label Grid.Row="1">Фамилия: </Label>
        <TextBox Grid.Column="1" Grid.Row="1" Text="{Binding Path=Surname}" />
         <ComboBox Grid.Row="3" Grid.Column="1" Name="boxRole" DisplayMemberPath="Name" SelectedValuePath="Id" SelectedValue="{Binding Path=RoleId, Mode=TwoWay}" />
</Grid>

<DataGridTextColumn Header="Роль" Binding="{Binding Path=Role.Name, Mode=OneWay}" />

<DataGridComboBoxColumn Header="Роль" x:Name="boxRole" DisplayMemberPath="Name" SelectedValuePath="Id"  SelectedValueBinding="{Binding Path=RoleId}"  />