如何获取 ADO.NET 实体模型中的外键？
我有3个表（以及实体模型中的相应实体） 游戏： Id - 主键 ...其他栏目
玩家： Id-主键 ...其他栏目
GamePlayer（一个玩家可以参加很多游戏） 游戏ID --> 游戏中的外键 玩家ID --> 来自 Player 的外键 ...其他列
在我的代码中，我可以通过其他方式使用 gameId 和 playerId 。 使用这个我想知道玩家（playerId）是否正在参与特定游戏（gameId）。 所以我这样做： (entities 是我的上下文对象)
IQueryable query =Entity.GamePlayer.where(gp => ((gp.Game.Id == gameId) && (gp.Player.Id ==玩家ID))) 如果查询返回一行，那么我就知道玩家正在参与该游戏。
我阅读了多个有关实体引用的 MSDN 博客，但我很困惑。 看来 MSDN 建议首先我必须检查 EntityReference 对象的 IsLoaded，如果未加载，我必须加载该实体，只有这样我才应该在查询中使用它。
GamePlayer 确实有 GamePlayer.GameReference 和 GamePlayer.PlayerReference，但我无法检查引用是否已加载，因为我手中没有 GamePlayer 对象。 GamePlayer 表保存两个 1...* 关系，仅此而已。 我必须仅使用 GameId 和 PlayerId 查询 GamePlayer。 我在这里做错了什么？
我是否应该获取 Player（或 Game）对象（使用它们的 Id）并检查 GamePlayer 实体集合？ Sql 就是这么简单。 如果这太天真了，抱歉，我很难将 sql 查询转换为实体查询。
I have 3 tables (and corresponding entities in the entity model)
Game:
Id - primay key
... other columns
Player:
Id - primary key
... other columns
GamePlayer (a player can participate in many games)
GameId --> foreign key from Game
PlayerId --> foreign key from Player
... other columns
In my code, I have gameId and playerId available to me thru' other means. Using this I want to know if the player (playerId) is participating in a particular game (gameId). So I'm doing this: (entities is my context object)
IQueryable query = entities.GamePlayer.where(gp => ((gp.Game.Id == gameId) && (gp.Player.Id == playerId)))
If the query returns a row, then I know that player is participating in that game.
I read multiple MSDN blogs on entity references and I'm confused. It appears that MSDN recommends that first I have to check the EntityReference object for IsLoaded and if not loaded, I have to load the entity and ONLY then I should use that in the query.
GamePlayer does have GamePlayer.GameReference and GamePlayer.PlayerReference, but I cannot check if reference is loaded because I dont have a GamePlayer object in hand. GamePlayer table holds the two 1...* relationships and thats about it. I have to query GamePlayer only using GameId and PlayerId. What am I doing wrong here?
Should I instead get the Player (or Game) object (using their Ids) and check the GamePlayer entity collection instead? Sql was so simple. If this is so naive, sorry, I'm having a tough time translating my sql query to entity queries.
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我认为你所做的很好。 据我所知，无论您在 lambda 表达式中使用什么，都不必显式加载。
我认为 MSDN 指的是如果您获取 GamePlayer 实体，然后访问关联实体，如下所示：
GamePlayer gp =Entity.GamePlayer.First( g=> g.id = 2);
string gameName = gp.Game.name;
这会引发异常（您必须单独加载游戏或确保它像这样加载：entities.GamePlayer.Include("Game").First( g => g.id = 2))
I think what you're doing is fine. As far as I know, whatever you use in the lambda-expression doesn't have to be loaded explicitly.
I think what MSDN is referring to is if you would get a GamePlayer entity and then access an associated entity like this:
GamePlayer gp = entities.GamePlayer.First( g=> g.id = 2);
string gameName = gp.Game.name;
That would throw an exception (you would have to either load the game separately or make sure it is loaded like this: entities.GamePlayer.Include("Game").First( g => g.id = 2))