如何缩短我的linq代码？

Question

hi; i try to run my codes. My program more slowly runnig. i need to give performance also write less codes in GetAliSpReqs(), GetMaintData();GetAccess....GET(... How can i write more effective below codes. They are too slow also not useful. forexample i try to write les than 1-2 line with GetAliSpReqs()? How can i ? please help me...

  public void LoadById(string SearchItem)
        {
            var myTechnicTasks = engTaskCtx.Tasks.Where(task => task.MyTechnicReference.StartsWith(SearchItem)).Select(task => new MyTask()
            {
                id = task.id,
                MyTechnicReference = task.MyTechnicReference,
                MPDReference = task.MPDReference,
                tasktypeid = task.tasktypeid,
                shortdesc = task.shortdesc,
                interval = task.interval,
                critical = task.critical,
                mandatory = task.mandatory,
                dupinsp = task.dupinsp,
                dualsystemmaint = task.dualsystemmaint,
                MPDSkill = task.MPDSkill,
                MPDCrew = task.MPDCrew,
                MPDAccessMH = task.MPDAccessMH,
                MPDTotalMH = task.MPDTotalMH,
                extratime = task.extratime,
                Team = task.Team,
                MaintData = EngGetCalculatedTaskField.GetMaintData(task.id),
                AliSpReqs = EngGetCalculatedTaskField.GetAliSpReqs(task.id),
                Access = EngGetCalculatedTaskField.GetAccess(task.id),
                preperation = task.preperation,
                longdesc = task.longdesc,
                applnotes = task.applnotes
            });
            MyTechnicTaskList = myTechnicTasks.ToList();
        }




    public static class EngGetCalculatedTaskField
    {
        private static TaskMaintenanceDataDataContext engTaskCtx { get; set; }
        public static string GetMaintData(int taskID)
        {
            try
            {
                using (TaskCardContext.TaskMaintenanceDataDataContext dc = new TaskCardContext.TaskMaintenanceDataDataContext())
                {
                    string maintenanceData = String.Empty;

                    foreach (var item in dc.TaskRelations.Where(tableRaletions => tableRaletions.TaskId == taskID && tableRaletions.RelTypeId == 12))
                    {
                        maintenanceData += item.RefMaintenance.shortdesc + "; ";
                    }

                    return maintenanceData.Substring(0, maintenanceData.Length - 2);
              }
            }
            catch
            {
                return String.Empty;
            }

        }
        public static string GetAliSpReqs(int taskID)
        {
            #region Old
            try
            {
                using (TaskCardContext.TaskMaintenanceDataDataContext dc = new            TaskCardContext.TaskMaintenanceDataDataContext())
                {
                    string aliSpReqs = String.Empty;

                    foreach (var item in dc.TaskRelations.Where(tableRaletions => tableRaletions.TaskId == taskID && tableRaletions.RelTypeId == 13))
                    {
                        aliSpReqs += item.RefAliSpReq.shortdesc + "; ";
                    }
                    return aliSpReqs.Substring(0, aliSpReqs.Length - 2);


                }
            }
            catch
            {
                return String.Empty;
            } 
            #endregion


        }
        public static string GetAccess(int taskID)
        {
            #region Old
            try
            {
                using (TaskCardContext.TaskMaintenanceDataDataContext dc = new TaskCardContext.TaskMaintenanceDataDataContext())
                {
                    string access = String.Empty;

                    foreach (var item in dc.TaskRelations.Where(tableRaletions => tableRaletions.TaskId == taskID && tableRaletions.RelTypeId == 15))
                    {
                        access += item.RefAccessPanel.shortdesc + "; ";
                    }
                    return access.Substring(0, access.Length - 2);


                }
            }
            catch
            {
                return String.Empty;
            } 
            #endregion

        }
}

Answer 1

Let's take this bit of code as an example:

string aliSpReqs = String.Empty;

foreach (var item in dc.TaskRelations.Where(tableRaletions => 
                  tableRaletions.TaskId == taskID 
                  && tableRaletions.RelTypeId == 13))
{
    aliSpReqs += item.RefAliSpReq.shortdesc + "; ";
}
return aliSpReqs.Substring(0, aliSpReqs.Length - 2);

You're concatenating strings in a loop. That's a bad idea. Instead, try this (assuming .NET 4):

var query = c.TaskRelations.Where(r => r.TaskId == taskID 
                                       && r.RelTypeId == 13))
                           .Select(r => r.RefAliSpReq.shortdesc);
return string.Join("; ", query);

In .NET 3.5 you'd need to use this instead:

var query = c.TaskRelations.Where(r => r.TaskId == taskID 
                                       && r.RelTypeId == 13))
                           .Select(r => r.RefAliSpReq.shortdesc);
return string.Join("; ", query.ToArray());

Admittedly I can't tell whether that's actually what's making this slow or not - but it could well be, if there are a lot of strings.

As an aside, this is a terrible idea:

catch
{
    return String.Empty;
}

Catch specific exceptions instead - or in most cases, just let the exception propagate to the caller. At the very least you should log the exception so you know what's going wrong.

Answer 2

All of your functions are calling the same piece of code with a different parameter:

try
{
    using (TaskCardContext.TaskMaintenanceDataDataContext dc = new TaskCardContext.TaskMaintenanceDataDataContext())
    {
        string aliSpReqs = String.Empty;

        foreach (var item in dc.TaskRelations.Where(tableRaletions => tableRaletions.TaskId == taskID && tableRaletions.RelTypeId == 13))
        {
            aliSpReqs += item.RefAliSpReq.shortdesc + "; ";
        }
        return aliSpReqs.Substring(0, aliSpReqs.Length - 2);
    }
}
catch
{
    return String.Empty;
}

So lets make a function out of it:

private static string GetData(int taskID, int typeID)
{
    try
    {
        using (TaskCardContext.TaskMaintenanceDataDataContext dc = new TaskCardContext.TaskMaintenanceDataDataContext())
        {
            //This was taken from Jons answer!!
            var query = c.TaskRelations.Where(r => r.TaskId == taskID 
                                              && r.RelTypeId == typeID))
                                       .Select(r => r.RefAliSpReq.shortdesc);
            return string.Join("; ", query.ToArray());
        }
    }
    catch
    {
        return String.Empty;
    }
}

Now you can call this function from all your other functions like:

public static string GetMaintData(int taskID)
{
    return GetData(taskID, 12);
}

So this makes your code much shorter. For a performance boost you should take Jons answer and do the concatenation of your string at last and not at every step by using += , cause this is very bad.