AsEnumerable -不包含“GetAwaiter”的定义

Question

使用实体框架核心6，我有以下内容：

IEnumerable<Orders> orders = await _dbContext.Orders.Where(x => x.Closed == null).AsEnumerable();

foreach (Order order in orders) {
  // Do something
}

我知道错误：

'IEnumerable<Order>' does not contain a definition for 'GetAwaiter' and no accessible extension method 'GetAwaiter' accepting a first argument of type 'IEnumerable<Order>' could be found (are you missing a using directive or an assembly reference?)

在这种情况下，我应该使用ToListAsync()吗？我理解这些选择：

IQueryable<Order> orders = _context.Orders.Where(x => x.Closed == null).AsQueryable();

IList<Order> orders = await _context.Orders.Where(x => x.Closed == null).ToListAsync();

但是AsEnumerable到底做了什么呢？

Answer 1

AsEnumerable()返回在枚举开始时同步执行查询的IEnumerable，因此没有Task等待。如果必须异步枚举，请使用AsAsyncEnumerable()和await foreach

var orders = await _dbContext.Orders.Where(x => x.Closed == null)
    .AsAsyncEnumerable();

await foreach (Order order in orders) 
{
   // Do something
}