[SalesForce] Setting field values generic SObject

Using mauForceDev's answer I've written out a far more fleshed out version.

Please note, my actual implementation is not the version I'm posting here (it's far more complex), so this version is untested. But it should work fine.....

First, define a results class and a method to automate going from an unknown object ID into a set of results that gives us the related field we are looking for and the original ID's object. Everything we need to start processing data! :)

    public class fieldHunterResults{
        public String fieldName = '';
        public String objectType = '';
        public Boolean isFound = false;
    }

    public fieldHunterResults fieldHunt(Id related_object_id,String field_type){

        fieldHunterResults results = new fieldHunterResults();

        //Just make sure null isn't sent
        if(related_object_id!=null){
            Schema.SObjectType token = related_object_id.getSObjectType();
            Schema.DescribeSObjectResult dr = token.getDescribe();

            //Foreach field
            for(Schema.Sobjectfield field : dr.fields.getMap().values()){
                //Check to see if there is any related fields
                List<Schema.SObjectType> related_fields = field.getDescribe().getReferenceTo();
                if(related_fields.size()>0){
                    SObjectType related_field = related_fields[0];
                    //Check to see if the related fields matchs the one we are looking for
                    if(related_field.getDescribe().getName()==field_type){
                        //Eureka! Found the related field! Fill up the results with what we found and return
                        results.fieldName = field.getDescribe().getName();//These lines can be optimised
                        results.objectType = token.getDescribe().getName();//These lines can be optimised
                        results.isFound = true;
                        return results;
                    }
                }

            }
        }
        //Nothing was found :( 
        return results;

    }

An example of how to use:

fieldHunterResults check_fields = fieldHunt(some_object_id,'Account');

    //Perform a dynamic SOQL based on the info we grabbed. We have grabbed the relevant information for this, field and object name
    if(check_fields.isFound){
        List<sObject> L = Database.query('SELECT '+check_fields.fieldName+' FROM ' + check_fields.objectType +' WHERE Id =:some_object_id');
        Account account = new Account(Id=L[0].get('Id'));//Don't do this in production, this is shorthand and prone to errors. But fine for an example
        account.Some_Value__c = 'Something';
        update account;
    }

SObject is an abstract class. You can't directly instantiate SObject itself, as the platform requires that the contained SObject knows what type it is (because of the validation for which fields are legal, what data type each field has, etc).

You can determine what type of SObject you're working with by checking the ID. For example, a FeedItem trigger might look like this:

trigger X on FeedItem (after insert) {
    map<id, sobject> parents = new map<id, sobject>();
    set<sobjecttype> types = new set<sobjecttype>();
    for(FeedItem record: Trigger.new) {
        parents.put(record.parentid, null);
        types.add(record.parentid.getsobjecttype());
    }
    for(sobjecttype stype: types) {
        parents.putall(query.fortype(stype, parents.keyset()));
    }
    // Do something with the data you now have
}

I left out the "Query.forType" function in this post, because one should build the queries according to one's needs.