Question

我有一个WebAPI控制器需要从数据库返回一个集合，但我还需要从某些实体中删除一些属性。但是，出于某种原因，当我在调试模式中单步执行代码时，表示另一个实体的属性将返回null，除了有时。我已经在下面显示了json响应，其中显示Sport，HomeTeam和AwayTeam为null：

但是当我在调试模式中跳过代码时，我得到了预期的结果：

相关的控制器方法如下

public dynamic Get()
{
    var allPicks = _db.Picks;
    if (User.Identity.IsAuthenticated)
    {
        string userId = User.Identity.GetUserId();
        var picks = _db.UnlockedPicks
            .Include(p => p.SelectedPick.AwayTeam)
            .Include(p => p.SelectedPick.HomeTeam)
            .Include(p => p.SelectedPick.Sport)
            .Where(p => p.UserId == userId);

        var unlockedPicks = picks.Select(p => p.SelectedPick);
        var otherPicks = allPicks.Except(unlockedPicks).Select(p => new
        {
            Analysis = "",
            PickSummary = "",
            Title = p.Title,
            Id = p.Id,
            Sport = p.Sport,
            HomeTeam = p.HomeTeam,
            AwayTeam = p.AwayTeam,
            MatchTime = p.MatchTime,
            PublishTime = p.PublishTime
        });
        return new
        {
            UnlockedPicks = unlockedPicks.OrderByDescending(p => p.MatchTime),
            OtherPicks = otherPicks.OrderByDescending(p => p.MatchTime)
        };
    }
    var publicPicks = allPicks.OrderByDescending(p => p.MatchTime).Select(p => new
    {
        Analysis = "",
        PickSummary = "",
        Title = p.Title,
        Id = p.Id,
        Sport = p.Sport,
        HomeTeam = p.HomeTeam,
        AwayTeam = p.AwayTeam,
        MatchTime = p.MatchTime,
        PublishTime = p.PublishTime
    });
    return new { UnlockedPicks = new Pick[0], OtherPicks = publicPicks };
}

没有Include()它每次都返回null但是我怎样才能让它每次返回预期的结果？

Answer 1

这是因为您没有使用延迟加载。延迟加载延迟时，您必须调用function YPE_bstab(&$item_output, $item) { $YPE_categories = get_terms('category', array( 'orderby' => 'count', 'number' => $item->items_num, 'order' => 'DESC', 'hide_empty' => 1 )); $item_output .= '<ul class="nav nav-tabs">'; foreach ($YPE_categories as $YPE_category) { $item_output .= '<li>'; $item_output .= '<a href="#'.$YPE_category->slug.'" data-toggle="tab">'.$YPE_category->name.'</a>'; $item_output .= '</li>'; } $item_output .= '</ul>'; $item_output .= '<div class="tab-content">'; foreach ($YPE_categories as $YPE_category) { $item_output .= '<div class="tab-pane" id="'.$YPE_category->slug.'">'; $YPE_Query = array('posts_per_page' => $item->items_num,'category_name' => $YPE_category->slug); $YPE_cat_query = new WP_Query($YPE_Query); while ($YPE_cat_query->have_posts()) { $YPE_cat_query->the_post(); $item_output .= '<a href="'.get_permalink().'">'.get_the_post_thumbnail(get_the_ID()).'</a>'; $item_output .= '<p><a href="'.get_permalink().'">'.get_the_title().'</a></p>'; } wp_reset_query(); $item_output .= '</div>'; } $item_output .= '</div>'; }才能加载导航属性。如果要加载所有导航属性而不调用Include，则必须激活延迟加载，这可以通过上下文的构造函数完成。像这样：

Include

默认情况下应激活延迟加载。您可能已将其停用在代码中的其他位置。每次在调试模式下检查导航属性时，也会自动调用它。

EF有时在外键类型上返回null

1 个答案: