LINQ IQIeryable到IEnumerable

Question

我尝试使用LINQ从3个表中获取数据以返回IEnumerable<PortalUser>但没有太多运气。当我想要返回结果时，它的类型为IQueryable<PortalUser>，我不确定为了达到目标我应该做些什么：

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;
}

在我的选择中，我尝试使用PortalUser构造函数来制作PortalUsers，并认为这会给我我想要的但显然没有。

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; }
}

我收到此错误：

  

无法将'System.Linq.IQueryable<BSAR.Services.Models.Outbound.Full.PortalUser>'类型隐式转换为'System.Threading.Tasks.TaskSystem.Collections.Generic.IEnumerable<BSAR.Services.Models.Outbound.Full.PortalUser'>。存在显式转换（您是否错过了演员？）

Answer 1

执行CodeCaster建议＆＃34;您可以更改返回类型吗？如果没有，为什么不标记方法async并返回await res.ToListAsync（）？你真的想做什么？＆＃34;

    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

Answer 2

GetUsers不会返回任务 - 因此您必须将返回类型更改为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;
}