Improving Performance of Calculated Properties

Question

I'm using calculated properties to roll up information about related entities.  Things were working great with only a few items, but after loading a large amount of data my performance is terrible.

I have a Group, which has many GroupAssignments (each containing a Volunteer), and each Volunteer has many Assignments. 

On the Volunteer Entity I have a calculated property for "AttendanceRate" which is:

this.Assignments.Where(x => x.Show.ShowCallTime < DateTime.Now && x.IsPresent == false).Count() /
this.Assignments.Where(x => x.Show.ShowCallTime < DateTime.Now).Count()

On the Group Entity I have a calculated property for "GroupAttendanceRate" which is:

this.GroupAssignments.Select(x => x.Volunteer).Where(x => x.IsActive == true).Average(x => x.AttendanceRate);

What I would like to do is display a screen that that shows the a list of groups and their GroupAttendanceRate.  I'm watching the activity through fiddler, and there is one request for Groups, and then a seperate request to get the GroupAssignments for each item in Groups.  Then there is a seperate request for each Volunteer related to the Group.

So basically, in order to calculate the GroupAttendanceRate, it requests EVERY volunteer in that group.  Loading a list with 10 groups each with 100 Volunteers generates 1000 seperate http requests.

What are my options for optomizing this? 

I have considered changing them from calculated properties to properties that are actually calculated and saved in the database in the _Updating and _Inserting functions, but that seems counter-intuitive.  Also, because they involve comparisons to DateTime.Now they do need to be recalculated when they are requested. 

Is there a way to make the calculated properties get calculated on the server side on the intial request to Groups()? 

Answer 1

There are 4 ways to display records with aggregated information (without computed properties):

1. Use SQL calculated columns (only useful if your data is an attached database)
2. Use a SQL View (again for an attached database)
3. Use "real" properties (using the Inserting/Updating methods that you described above)
4. Use a custom RIA service

The best way, in my opinion, is to create a custom RIA service.

This article link below will show you all the techniques that you'll need. It's VERY easy. And the performance is greatly improved over computed properties.

How Do I: Display a Chart Built On Aggregated Data

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Answer 2

@Angie - please propose an answer before marking it, then give the OP a reasonable amount of time to confirm it.

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Answer 3

For the "real" properties solution you can also use the _Changed method to calculate the property.  This will give you the client tier response similar to a computed property and remove some of the processing involved with the inserting/updating methods.

Answer 4

Quite true! Thanks for pointing that out. :-)

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Yann - LightSwitch Central - Click here for FREE Themes, Controls, Types and Commands

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Answer 5

Just a followup, I wrote a WCF RIA service, copied my formulas for the computed methods into the WCF RIA service, and it is working well.

I only put the computed fields in the new class, as I don't want to duplicate defining all of the other fields.

However, in my screen, I want to use a grid view to display the all of the fields from the original entity as well as all of the computed fields on one row.

Is there a good way to do this?  Or do I need to "copy over" the values from the original data source to my WCF RIA service?