LINQ IQueryable到IEnumerable

Question

我想從3個表中使用LINQ返回一個IEnumerable<PortalUser>但沒有太多運氣的數據。當我想返回的結果，這是IQueryable<PortalUser>型的，我不知道我應該爲了達到我的目標是做：

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; 
} 

在我的選擇，我嘗試使用PortalUser構造函數使PortalUsers，並認爲這會給我我想要的，但顯然不是。

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; } 
} 

我得到這個錯誤：

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不返回任務 - 因此你必須改變返回類型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

做什麼CodeCaster建議「你可以改變返回類型嗎？如果沒有，爲什麼你不標記方法異步並返回等待res.ToListAsync（）？你真的想要做什麼？「

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(); 
    } 

這解決了我的問題，謝謝