是否可以使用await和使用自定义函数的查询

Question

我想在继续执行其他任何操作之前等待此查询。我已经看到了这个主题的几个问题，但是没有一个在查询中使用自定义函数，这使得它有点棘手。以下查询甚至可以使用await。我正在使用使用Microsoft异步包.NET4.0的await，异步（https://www.nuget.org/packages/Microsoft.Bcl.Async/）

var Employees = 
    (from d in context.Employees 
    join a in context.Address on d.ID equals a.EmployeeID 
    select new 
    { 
     Employee = d, 
     Address = a, 
    }) 
    .AsEnumerable() memory 
    .Select(x => new Employee 
    { 
     Id = x.Employee.Id, 
     PreferredName = GetPreferredName(x.Employee.FirstName, x.Employee.MiddleName, x.Employee.LastName, x.Employee.Alias), 
     StreetAddress = x.Address.StreetAddress 
    }) 
    .ToList(); 

private string GetPreferredName(string firstName, string middleName, string lastName, string dnsName) 
     { 
      if (!string.IsNullOrEmpty(firstName)) 
      return firstName; 
      else if (!string.IsNullOrEmpty(middleName)) 
       return middleName; 
      else if (!string.IsNullOrEmpty(lastName)) 
       return lastName; 
      else if (!string.IsNullOrEmpty(dnsName)) 
       return dnsName; 

      return ""; 
     } 

Answer 1

您可以使用ToListAsync来异步获取EF查询的结果。

var query = await 
    (from d in context.Employees 
    join a in context.Address on d.ID equals a.EmployeeID 
    select new 
    { 
     Employee = d, 
     Address = a, 
    }) 
    .ToListAsync(); 

var Employees = query  
    .Select(x => new Employee 
    { 
     Id = x.Employee.Id, 
     PreferredName = GetPreferredName(x.Employee.FirstName, x.Employee.MiddleName, x.Employee.LastName, x.Employee.Alias), 
     StreetAddress = x.Address.StreetAddress 
    }) 
    .ToList(); 

Answer 2

您可以使用await的ToListAsync()代替ToList()，如果你把它在内存之前调用您查询的第一部分：

var queryEmployees = await 
(from d in context.Employees 
join a in context.Address on d.ID equals a.EmployeeID 
select new 
{ 
    Employee = d, 
    Address = a, 
}).ToListAsync(); 

var employees = Employees.Select(x => new Employee 
{ 
    Id = x.Employee.Id, 
    PreferredName = GetPreferredName(x.Employee.FirstName, x.Employee.MiddleName, x.Employee.LastName, x.Employee.Alias), 
    StreetAddress = x.Address.StreetAddress 
}) 
.ToList();