c# - Entity Framework 中的 Linq 查询优化

Question

我有以下查询，我正在寻找的是优化 where 子句。我不喜欢多次使用 FirstOrDefault。有没有一种方法可以通过 Join 或其他方式来实现它，这样我就可以只访问一次 FirstOrDefault？

var promos = await this._context
                       .SinglePromotions
                       .Include(p => p.Rewards)
                       .Include(p => p.InAppProduct)
                       .Include(p => p.PlayerSinglePromotions)
                       .ThenInclude(sp => sp.Player)
                       .ThenInclude(pl => pl.Purchases)
                       .Where(p => p.MinimumPlayerLevel <= Player.Level && 
                                   p.Placement == placement && 
                                   p.IsActive && 
                                   (p.PlayerSinglePromotions.All(sp => sp.PlayerID != Player.ID) || 
                                    (p.PlayerSinglePromotions.FirstOrDefault(sp => sp.PlayerID == Player.ID).PurchaseAmount < p.PurchaseLimit)) &&
                                    (p.PlayerSinglePromotions.All(sp => sp.PlayerID != Player.ID) || (p.PlayerSinglePromotions.FirstOrDefault(sp => sp.PlayerID == Player.ID).Player.Purchases.Count <= p.MaxInAppPurchasesByPlayer))
                       )
                       .ToListAsync();

Answer 1

嗯，可能有更好的解决方案，但您可以使用 Any 扩展方法替换使用 FirstOrDefault 的条件:

var promos = await this._context.SinglePromotions
.Include(p => p.Rewards)
.Include(p => p.InAppProduct)
.Include(p => p.PlayerSinglePromotions)
    .ThenInclude(sp => sp.Player)
    .ThenInclude(pl => pl.Purchases)
.Where(
    p => p.MinimumPlayerLevel <= Player.Level && 
    p.Placement == placement && 
    p.IsActive &&
   (p.PlayerSinglePromotions.All(sp => sp.PlayerID != Player.ID) ||
    p.PlayerSinglePromotions.Any(sp => sp.PlayerID == Player.ID 
                                   && (sp.Player.Purchases.Count <= p.MaxInAppPurchasesByPlayer || sp.PurchaseAmount < p.PurchaseLimit))))
.ToListAsync();