LINQ IQueryable到IEnumerable

Question

我想从3个表中使用LINQ返回一个IEnumerable<PortalUser>但没有太多运气的数据。当我想返回的结果，这是IQueryable<PortalUser>型的，我不知道我应该为了达到我的目标是做：

public Task<IEnumerable<PortalUser>> GetUsers(string accountCode) 
{ 
    var res = from u in _db.Users 
       join ur in _db.UserRoles on u.ContactGuid equals ur.ContactGuid 
       join r in _db.Roles on ur.RoleId equals r.Id 
       where ur.AccountCode == accountCode 
       select(new PortalUser(u.Id, u.FriendlyName, u.UserName, r.RoleName)); 
    return res; 
} 

在我的选择，我尝试使用PortalUser构造函数使PortalUsers，并认为这会给我我想要的，但显然不是。

public class PortalUser 
{ 
    public PortalUser(int id,string friendlyName,string username,string rolename) 
    { 
     Id = id.ToString(); 
     Firstname = friendlyName.Split(' ')[0]; 
     Lastname = friendlyName.Split(' ')[1]; 
     Username = username; 
     Role = rolename; 
    } 

    public string Id { get; set; } 
    public string Firstname { get; set; } 
    public string Lastname { get; set; } 
    public string Username { get; set; } 
    public string Role { get; set; } 
} 

我得到这个错误：

Cannot implicitly convert type 'System.Linq.IQueryable<BSAR.Services.Models.Outbound.Full.PortalUser>' to 'System.Threading.Tasks.TaskSystem.Collections.Generic.IEnumerable<BSAR.Services.Models.Outbound.Full.PortalUser'> . An explicit conversion exists (are you missing a cast?)

Answer 1

GetUsers不返回任务 - 因此你必须改变返回类型IEnumerable<PortalUser>：

public IEnumerable<PortalUser> GetUsers(string accountCode) 
{ 
    var res = from u in _db.Users 
     join ur in _db.UserRoles on u.ContactGuid equals ur.ContactGuid 
     join r in _db.Roles on ur.RoleId equals r.Id 
     where ur.AccountCode == accountCode 
     select (new PortalUser(u.Id, u.FriendlyName, u.UserName, r.RoleName)); 
    return res; 
} 

Answer 2

做什么CodeCaster建议“你可以改变返回类型吗？如果没有，为什么你不标记方法异步并返回等待res.ToListAsync（）？你真的想要做什么？“

public async Task<IEnumerable<PortalUser>> GetUsers(string accountCode) 
    { 
     var res = from u in _db.Users 
        join ur in _db.UserRoles on u.ContactGuid equals ur.ContactGuid 
        join r in _db.Roles on ur.RoleId equals r.Id 
        where ur.AccountCode == accountCode 
        select (new PortalUser(u.Id, u.FriendlyName, u.UserName, r.RoleName)); 
     return await res.ToListAsync(); 
    } 

这解决了我的问题，谢谢