FindAsync 和 Include LINQ 语句

问题描述

到目前为止我得到的代码运行良好

The code I have got so far works fine

public async Task<ActionResult> Details(Guid? id)
{
    if (id == null)
    {
        return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
    }

    ItemDetailModel model = new ItemDetailModel();
    model.Item = await db.Items.FindAsync(id);
    if (model.Item == null)
    {
        return HttpNotFound();
    }

    return View(model);
}

但我想多包含 1 个表，不能使用 FindAsync

But I want to include 1 table more and cannot use FindAsync

public async Task<ActionResult> Details(Guid? id)
{
    if (id == null)
    {
        return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
    }

    ItemDetailModel model = new ItemDetailModel();
    model.Item = await db.Items.Include(i=>i.ItemVerifications).FindAsync(id);

    if (model.Item == null)
    {
        return HttpNotFound();
    }

    return View(model);
}

所以我遇到了这个错误

严重性代码描述项目文件行抑制状态错误 CS1061 'IQueryable' 不包含'FindAsync' 并且没有扩展方法 'FindAsync' 接受第一个可以找到IQueryable"类型的参数(您是否缺少使用指令还是程序集引用?)

有什么办法解决吗?

推荐答案

最简单的就是用FirstOrDefaultAsync或者SingleOrDefaultAsync代替:

The simplest is to use FirstOrDefaultAsync or SingleOrDefaultAsync instead:

model.Item = await db.Items.Include(i => i.ItemVerifications)
    .FirstOrDefaultAsync(i => i.Id == id.Value);

您收到错误的原因是因为 Find/FindAsync 方法是为 DbSet 定义的，但结果是 包含是IQueryable<T>.

The reason you are getting the error is because Find / FindAsync methods are defined for DbSet<T>, but the result of Include is IQueryable<T>.

另一种方法是将 FindAsync 与 显式加载:

Another way is to combine FindAsync with explicit loading:

model.Item = await db.Items.FindAsync(id);
if (model.Item == null)
{
    return HttpNotFound();
}
await db.Entry(model.Item).Collection(i => i.ItemVerifications).LoadAsync();

这篇关于FindAsync 和 Include LINQ 语句的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！