Question

我在MVC 4 Web API控制器上有以下方法。

public JsonResult GetJourney(List<string> assetIds, DateTime start, DateTime finish)
{
    var journey = new List<JourneyPoint>();

    var startUTC = start.ToUniversalTime();
    var finishUTC = finish.ToUniversalTime();

    foreach (var assetId in assetIds)
    {
        string id = assetId;

        var events = _eventRepo.GetAll().Where(evt => evt.EventTypeId == 0 && evt.TimeStamp > startUTC && evt.TimeStamp < finishUTC && evt.AssetId == id);

        foreach (var @event in events)
        {
            var myGps = _gpsRepo.GetAll().FirstOrDefault(gps => gps.Id == @event.GPSId);

            if (myGps != null)
            {
                var myJourneyPoint = new JourneyPoint
                {
                    Id = @event.Id,
                    AssetId = @event.AssetId,
                    TimeStamp = @event.TimeStamp.ToUnixEpocSeconds(),
                    Lat = myGps.Lat,
                    Long = myGps.Long,
                    Speed = myGps.Speed,
                    Elevation = myGps.Elevation,
                    Heading = myGps.Head
                };
                journey.Add(myJourneyPoint);
            }
        }
    }

    var jsonJourney = Json(journey.OrderBy(ju => ju.TimeStamp).ToList());
    jsonJourney.JsonRequestBehavior = JsonRequestBehavior.AllowGet;
    return jsonJourney;
}

使用repo方法：

public IQueryable<Event> GetAll()
{
    var db = new CasLogEntities();
    return db.Event;
}

public IQueryable<GPS> GetAll()
{
    var db = new CasLogEntities();
    return db.GPS;
}

这一切都很好用，并且使用存储库允许我为控制器代码编写测试套件。

虽然我怀疑这段代码是低效的，但是对数据库有多次调用，而且很多计算工作都是由.Net而不是sql server完成的。

Re-sharper建议我可以将每个循环转换为linq语句，我这样做并最终得到以下代码。

public JsonResult GetJourney(List<string> assetIds, DateTime start, DateTime finish)
{
    var journey = new List<JourneyPoint>();

    var startUTC = start.ToUniversalTime();
    var finishUTC = finish.ToUniversalTime();

    foreach (var assetId in assetIds)
    {
        string id = assetId;

        var events = _eventRepo.GetAll().Where(evt => evt.EventTypeId == 0 && evt.TimeStamp > startUTC && evt.TimeStamp < finishUTC && evt.AssetId == id);

        journey.AddRange(from @event in events
                         let myGps = _gpsRepo.GetAll().FirstOrDefault(gps => gps.Id == @event.GPSId)
                         where myGps != null
                         select new JourneyPoint
                         {
                             Id = @event.Id,
                             AssetId = @event.AssetId,
                             TimeStamp = @event.TimeStamp.ToUnixEpocSeconds(),
                             Lat = myGps.Lat,
                             Long = myGps.Long,
                             Speed = myGps.Speed,
                             Elevation = myGps.Elevation,
                             Heading = myGps.Head
                         });
    }

    var jsonJourney = Json(journey.OrderBy(ju => ju.TimeStamp).ToList());
    jsonJourney.JsonRequestBehavior = JsonRequestBehavior.AllowGet;
    return jsonJourney;
}

但是，当我运行此代码时出现错误：

LINQ to Entities无法识别方法＆＃39; System.Linq.IQueryable`1 [CasWeb.Models.DataContext.GPS] GetAll（）＆＃39;方法，并且此方法无法转换为商店表达式。

我理解这是因为LINQ To Entities试图映射＆＃34; GetAll（）＆＃34; sql的方法，它不能。

我的问题是：如何重写我的代码以避免此错误并尽可能多地执行SQL服务器？如果可能的话，维护存储库模式以便进行测试？

Answer 1

正如@Rup在评论中建议的那样，以下内容应避免错误。

    journey.AddRange(from @event in events
                 join gps in _gpsRepo.GetAll() on gps.Id == @event.GPSId
                 select new JourneyPoint
                 {
                     Id = @event.Id,
                     AssetId = @event.AssetId,
                     TimeStamp = @event.TimeStamp.ToUnixEpocSeconds(),
                     Lat = gps.Lat,
                     Long = gps.Long,
                     Speed = gps.Speed,
                     Elevation = gps.Elevation,
                     Heading = gps.Head
                 });

我如何重写此代码以避免“Linq to entities无法识别方法”错误

1 个答案: