Question

我正在尝试优化下面的代码，逐个循环遍历对象并进行数据库查找。我想创建一个LINQ语句，它将在一个事务中执行相同的任务。

这是我效率低下的循环代码;

IStoreUnitOfWork uow = StoreRepository.UnitOfWorkSource.GetUnitOfWorkFactory().CreateUnitOfWork(); 
var localRunners = new List<Runners>();
foreach(var remoteRunner in m.Runners) {                                                           
    var localRunner = uow.CacheMarketRunners.Where(x => x.SelectionId == remoteRunner.SelectionId && x.MarketId == m.MarketId).FirstOrDefault();  
    localRunners.Add(localRunner);
}

这是我在单个查询中尝试做同样事情的非常可行的尝试。嗯，这甚至不是一次尝试。我不知道从哪里开始。 remoteRunners对象具有复合键。

IStoreUnitOfWork uow = StoreRepository.UnitOfWorkSource.GetUnitOfWorkFactory().CreateUnitOfWork(); 
var localRunners = new List<Runners>();
var localRunners = uow.CacheMarketRunners.Where(x =>
   x.SelectionId in remoteRunners.SelectionId &&
   x.MarketId    in remoteRunners.MarketId);

感谢您寻找

Answer 1

所以你有一个对象m，它有一个属性MarketId。对象m也有一系列Runners，其中每个Runner都有一个属性SelectionId。

您的数据库有CacheMarketRunners。每个CacheMarketRunner都有MarketId和SelectionId。

您的查询应返回CacheMarketRunners所有MarketId等于m.MarketId和SelectionId m.Runners.SelectionId的所有m。

如果您的Runners没有太多var requestedSelectionIds = m.Runners.Select(runner => runner.SelectionId); var result = CacheMarketRunners.Where(cacheMarketRunner => cacheMarketRunner.MarketId == m.MarketId && requestedSelectionIds.Contains(cacheMarketRunner.SelectionId));，少于250，请考虑使用Queryable.Contains

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Answer 2

要提高性能，您需要缓存交易结果：

var marketRunners = uow.CacheMarketRunners.Where(x => x.MarketId == m.MarketId).ToList();

有关uow的交易结果存储在List中，因此您在for循环中没有交易。因此应该提高绩效：

var localRunners = new List<Runners>();
foreach(var remoteRunner in m.Runners) {                                                           
    var localRunner = marketRunners.FirstOrDefault(x => x.SelectionId == remoteRunner.SelectionId);
    localRunners.Add(localRunner);
}

您甚至可以删除for循环：

var localRunners = m.Runners.Select(remoteRunner => marketRunners.FirstOrDefault(x => x.SelectionId == remoteRunner.SelectionId)).ToList();

如何将此循环代码转换为单个LINQ实现？

2 个答案: