Question 320756 in ASP.NET Question posted in
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Asp.net – How to filter and group records efficiently in C#

A table Work has three columns: ID, Region and Worker.

And there are two DropDown lists.

DropDown A: Select and filter the Region, is bound to region with data regions

DropDown B: Select and filter the Worker, is bound to worker with data workers

The flow: user selects region, then selects worker of that region

Initialize:

List<Work> works = new(); 
works = GetWorks(); //get all the records from the table
List<string> regions = new();
List<string> workers = new();
regions = works.Select(w=>w.region).Distinct().ToList();

When the user selects a region

workers = works.Where(w=>w.Region == region).Select(w=>w.worker).Distinct().ToList();

However, it would be incredibly slow when there are thousands of records.

How can I achieve this more efficently? Thanks!

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2

Answers


  1. 0

    It seems like GetWorks might be returning a List or an IEnumerable. The issue here is that loading all those data into memory can be problematic. Essentially, the solution involves delegating the work to the database: make GetWorks return an IQueryable. This way, when you execute works.select(w => w.region).Distinct(), that operation will be performed in the database. The same goes for works.select(w => w.region).Distinct(). You can achieve this only if you’re working in BlazorServer.

    If you are working in Blazor-WASM, you’ll need to expose the services GetRegions and GetWorkers.

    Bonus track: Normalize database and create Region model.

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  2. 0

    I think that your program is slow because the GetWorks() returns a List<Work>.
    Keep in mind that using Linq on a List, you are doing all the work on the machine. You can try refactoring your code exposing an IQueryable if you are using Entity Framework (even if is not a best practice).
    Or you could call the GetWorks with the filters and delegate the work to the database.

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