I want to get id of product selected on opportunity record

Question

I want to get id of product selected on opportunity record. There is lookup relationship between Opportunity and product. All I want is id of the product selected by user on that record. below is my code.

    public without sharing class Test {

    public static void Org (List<Opportunity> organisations){
   Set<Id> OrgIds = new Set<Id>();


 for(Opportunity o : organisations){

            OrgIds.add(o.Id);
        }

 for( Product__c product : [SELECT ID, Name, Product_ID__c FROM Product__c WHERE ID IN :OrgIds])
        {
        system.debug('I am in here' + product.ID );
       }

}
}

Product__C is a Custom object

Added lookup between opportunity and product object.

Answer 1

If the lookup field is on the Opportunity then you would need to query the opportunity object not the Product__c object. I'm guessing something like this:

public without sharing class Test {

  public static void Org (List<Opportunity> organisations){
    Set<Id> prodIds = new Set<Id>();

    for(Opportunity o : organisations) {
      prodIds.add(o.product__c);
    }

    for( Product__c product : [SELECT ID, Name, Product_ID__c FROM Product__c WHERE ID IN :prodIds])
    {
      system.debug('I am in here' + product.Product_ID__c );
    }

  }
}

Answer 2

The Ids that you're gathering in the for loop before the query are for Opportunities, not Product__c.

Your query should be on Opportunity, not on Product__c.