Question

I’m building an ASP.Net application with Entity Framework (Code First) and I’ve implemented a Repository pattern like the one in this example.

I only have two tables in my database. One called Sensor and one called MeasurePoint (containing only TimeStamp and Value). A sensor can have multiple measure points. At the moment I have 5 sensors and around 15000 measure points (approximately 3000 points for each sensor).

In one of my MVC controllers I execute the following line (to get the most recent MeasurePoint for a Sensor)

DbSet<Sensor> dbSet = context.Set<Sensor>();
var sensor = dbSet.Find(sensorId);
var point = sensor.MeasurePoints.OrderByDescending(measurePoint => measurePoint.TimeStamp).First();

This call takes ~1s to execute which feels like a lot to me. The call results in the following SQL query

SELECT 
[Extent1].[MeasurePointId] AS [MeasurePointId], 
[Extent1].[Value] AS [Value], 
[Extent1].[TimeStamp] AS [TimeStamp], 
[Extent1].[Sensor_SensorId] AS [Sensor_SensorId]
FROM [dbo].[MeasurePoint] AS [Extent1]
WHERE ([Extent1].[Sensor_SensorId] IS NOT NULL) AND ([Extent1].[Sensor_SensorId] = @EntityKeyValue1)

Which only takes ~200ms to execute, so the time is spent somewhere else.

I’ve profiled the code with the help of Visual Studio Profiler and found that the call that causes the delay is

System.Data.Objects.Internal.LazyLoadBehavior.<>c_DisplayClass7`2.<GetInterceptorDelegate>b_1(!0,!1)

So I guess it has something to do with lazy loading. Do I have to live with performance like this or are there improvements I can make? Is it the ordering by time that causes the performance drop, if so, what options do I have?

Update:
I’ve updated the code to show where sensor comes from.

Answer 1

What that will do is load the entire children collection into memory and then perform the .First() linq query against the loaded (appx 3000) children.

If you just want the most recent, use this instead:

context.MeasurePoints.OrderByDescending(measurePoint => measurePoint.TimeStamp).First();