Question

我遇到了多对多关系数据库的预处理查询问题。

DB模型如下所示：

播放器[1] --- [N] PlayerMatch [N] ----- [1]匹配

播放器可以有多个匹配，匹配可以使用 PlayerMatch附加多个播放器 表。

使用preprocessquery我想只返回给定 Player.Id 的对象。

获取给定PlayerID为
从PlayerMatch获取所有元素，其中PlayerMatch.Match.ID == records来自（1）并返回该PlayerMatch.Player instaces

我想到：

partial void PlayerOponents_PreprocessQuery(int? PlayerID, ref IQueryable<Player> query)
{
     var playerGames = from g in this.PlayerMatches
                       where g.Player.Id == PlayerID 
                       select g.Match;
     var oponents    = from m in this.PlayerMatches
                       where (from g in playerGames where m.Match.Id == g.Id select m)
                       select m.Player;
     query = oponents;
}

如何让它发挥作用？

Answer 1

我设法解决它。问题是Lightswitch只支持LINQ的子集。复杂查询有一些限制。

var oponentList = new List<Player>();
var matches = (from q in this.PlayerMatches where q.Players.Id == PlayerID select q.Matches).Execute();
foreach(Match match in matches)
{
    var oponents = (from q in this.PlayerMatches where q.Matches.Id == match.Id where q.Players.Id != PlayerID select q.Players).Execute();
    foreach (Player player in oponents)
    {
        oponentList.Add(player);
    }              
}
query = oponentList.AsQueryable().Take(oponentList.Count());

Answer 2

<强>更新

我的下面的代码实际上并没有正常工作......它只是返回数据库中第一个X数量的人并忽略了我手动填充的列表的实际内容。（也许它适用于早期版本的Lightswitch;请参阅https://social.msdn.microsoft.com/Forums/vstudio/en-US/3db15a5f-aedd-4619-a0cc-d9580a9cd921/can-i-replace-iqueryablemonthlybalance-query-with-generic-list-asqueryable-in-preprocessquery?forum=lightswitch。）

这是我现在使用的代码（工作正常）：

Role trainerRole = (from r in Roles where r.Name == "Trainer" select r).Single();
var trainerIds = trainerRole.PersonRoles.Select(pr => pr.Person.Id);
query = query.Where(p => trainerIds.Contains(p.Id));

非常感谢您发布答案。它帮助我找到了一个很好的解决方案，这有点简单：

partial void Trainers_PreprocessQuery(ref IQueryable<Person> query)
{
    var trainers = new List<Person>();
    Role trainerRole = (from r in Roles where r.Name == "Trainer" select r).Single();
    foreach (PersonRole pr in trainerRole.PersonRoles)
    {
        trainers.Add(pr.Person);
    }
    query = trainers.AsQueryable().Take(trainers.Count());
}

Lightswitch多对多预处理查询方法

2 个答案: