Question

我希望让所有球队都没有当前的球队，并让所有球队拥有4名或更多球员。我尝试编写这个linq lambda查询：

teams = connection.Team 
    .Join(connection.Player,
        t => t.ID,
        p => p.IDTeam,
        (t, p) => new { Team = t, Player = p })
    .Where(tp => tp.Player.IDTeam == tp.Team.ID
        && tp.Team.ID != team.ID
        && tp.Team.IsVisible == true
        && !tp.Team.DeleteDate.HasValue)
    .Select(tp => tp.Team)
    .ToList();

但我不能指望有多少球员拥有球队的条件。怎么做？对于info，SQL中的查询是哪个？谢谢你的帮助！

编辑：作为必需类（从DBFirst生成）：

Answer 1

根据上述类，您可以扩展Team类并添加Players导航属性。

添加导航属性时，请确保 Team 和 Player 表之间存在数据库关系。此外，如果需要，请配置您的DbContext。

public class Team
{
    //...other properties
    public virtual ICollection<Player> Players { get; set; }
}

当您添加导航属性时，实现您的要求将是微不足道的：

connection.Teams
          .Where(t => t.ID != team.ID && t.IsVisible == true && !t.DeleteDate.HasValue && t.Players.Count() >= 4)

Answer 2

尝试使用GroupBy（）：

var teams = (from tp in connection.Team
   join p in connection.Team on tp.Player.IDTeam equals p.Team.ID
   select new { Team = tp, Player = p })
   .Where(tp =>  tp.Team.IsVisible == true && !tp.Team.DeleteDate.HasValue)
   .GroupBy(x => x.Team.ID)
   .Where(x => x.Count >= 4)
   .ToList();

Answer 3

试试这个：

teams = connection.Team 
.Join(connection.Player,
    t => t.ID,
    p => p.IDTeam,
    (t, p) => new { Team = t, Player = p })
.Where(tp => tp.Player.IDTeam == tp.Team.ID
    && tp.Team.ID != team.ID
    && tp.Team.IsVisible == true
    && !tp.Team.DeleteDate.HasValue)
.Select(tp => tp.Team)
.ToList().GroupBy(i=>i.ID).Where(i=>i.Count()>=4);

Answer 4

这个怎么样？

var teams = 
           (from t in connection.Team
           join p in connection.Player on p.TeamId equals t.ID into playersInTeam
           select new 
           { 
                Team = t, 
                PlayersCount = playersInTeam.Count(x => x.TeamId == t.Id) 
           })
           .Where(x => x.PlayersCount >= 4)
           .ToList();

LINQ Lamba加入计数

4 个答案: