c# - 如何使用 Join 和 Where 返回 IList？

Question

如何使用 Linq 或 EF Join 等工具在 C# MVC 中实现连接和位置？

这是我要实现的等效 SQL。

select * from promotion P
JOIN PromotionsClaimed PC
on PC.PromotionId = P.objectid
where PC.userId = @USERID

此方法应返回用户的促销列表。首先，我得到所有促销的列表，然后我得到用户声明的促销的综合列表。这是我目前所拥有的。

    public IList<Promotion> GetRewardsForUser(string userId)
    {
        //a list of all available promotions
        IList<Promotion> promos =  _promotionLogic.Retrieve();

        //contains a list of Promotion.objectIds for that user
        IList<PromotionsClaimed> promosClaimed = _promotionsClaimedLogic.RetrieveByCriteria(t => t.userId == userId);

        //should return a list of the Promotion name and code for the rewards claimed by user, but a complete list of Promotion entities would be fine
        var selectedPromos =
            from promo in promos
            join promoClaimed in promosClaimed on promo.objectId equals promoClaimed.PromotionId
            select new { PromoName = promo.Name, PromoCode = promo.Code };

        return selectedPromos;
    }

我意识到这里有很多问题。我正在尝试学习 Linq 和 Entity Framework ，但我不知道如何将 where 子句添加到 IList 或者是否有更简单的方法来完成此操作。

在我看来，似乎有一种方法可以过滤促销列表，其中包含 promosClaimed 列表中的 Promotion.objectId，但我不知道语法。

Answer 1

 public IList<Promotion> GetRewardsForUser(string userId)
{
    //a list of all available promotions
    IList<Promotion> promos =  _promotionLogic.Retrieve();

    //contains a list of Promotion.objectIds for that user
    IList<PromotionsClaimed> promosClaimed = _promotionsClaimedLogic.RetrieveByCriteria(t => t.userId == userId);

    //should return a list of the Promotion name and code for the rewards claimed by user, but a complete list of Promotion entities would be fine
    var selectedPromos =
        (from promo in promos
        join promoClaimed in promosClaimed on promo.objectId equals promoClaimed.PromotionId
        select new { PromoName = promo.Name, PromoCode = promo.Code }).ToList();

    return selectedPromos;
}