FindAsync和包括LINQ语句 [英] FindAsync and Include LINQ statements

问题描述

到目前为止，我得到的代码可以正常工作

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);
        }

但是我想多包含1个表，并且不能使用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"不包含以下内容的定义: "FindAsync"，没有扩展方法"FindAsync"接受第一个 可以找到类型为"IQueryable"的参数(您是否缺少 使用指令还是程序集引用?)

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

任何提示如何解决?

推荐答案

最简单的方法是使用FirstOrDefaultAsync或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);

出现错误的原因是因为Find/FindAsync方法是为DbSet<T>定义的，但是Include的结果是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:

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和包括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IT屋！