c# - FindAsync 和 Include LINQ 语句

Question

我目前得到的代码工作正常

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);
}

但我想再包含 1 个表，不能使用 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);
}

所以我面临这个错误

Severity Code Description Project File Line Suppression StateError CS1061 'IQueryable' does not contain a definition for'FindAsync' and no extension method 'FindAsync' accepting a firstargument of type 'IQueryable' could be found (are you missing ausing directive or an assembly reference?)

知道如何解决吗？

Answer 1

最简单的是使用FirstOrDefaultAsync或 SingleOrDefaultAsync相反:

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为 DbSet<T> 定义了方法，但是 Include 的结果是IQueryable<T> .

另一种方法是结合FindAsync与 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();