Question

I have partial class TaxReportItem with partial method OnActualVolumeChanging(double value):

public partial class TaxReportItem 
{
      partial void OnActualVolumeChanging(double value)
     {
        if (Tax != null)
        {
            Payment = value*Tax.TaxRate;
        }
    }
}

In this method i want to get all collection of TaxReportItems that’s present in context(something like this):

  partial void OnActualVolumeChanging(double value)
    {
        var sum = 0.0;
        if (Tax != null)
        {
            Payment = value*Tax.TaxRate;

            foreach (var taxReportItem in ????)
            {
                sum += taxReportItem.Sum;
            }
        }
    }

How can i achieve this?

Answer 1

This is actually quite hard because you should never need this. If you need this, design of your entity object is wrong and it is doing something which should be done elsewhere. Single TaxReportItem should never need to know about other tax report items and load them from database unless other items are dependent on this item (they form an aggregate). In such case you should have navigation property to dependent items in the principal one.

To follow your question. If you need to load other items you must have instance of the context to do that. You can either get instance used to load current item and use it to load other entities (bad solution) or you can create a new instance of the context and use it to load other entities (even worse solution).

As you can see from the linked article getting current context instance from the entity itself is not easy and it has some prerequisites which goes back to the first paragraph. It is hard because it is wrong approach.