Basic Example of a Lookup?

Question

I'm am having a ridiculous time finding basic Trigger examples (background: no official training, have books, have experience elsewhere, figuring this out on my own).

I am trying to write an insanely simple trigger that does a Lookup. CountryList is on Lead, I have made a custom object CountryLists. I want to verify if CountryList from Lead exists in the field "Country" in object CountryLists.

I have tried several iterations of code and keep getting mixed up on my initial Trigger.new call versus looping through either the Custom Object or the Leads to find if it yields a null or not. Literally, IF NOT NULL, then (do things to the Lead). That's it.

Does someone have an example or source of examples? Googling such things is a crap-shoot anymore.

Thanks so much.

ADDED: EXPANDED REASONING

One of the things I will do if NULL is found is put a value "(Undefined)" into field REGION__C on the Lead.

As well, if it is NOT NULL, I will be populating REGION__C on the Lead with an equivelent Region variable from the matching CountryLists entry.

Effectively.... United States of America will get a Region__c _ of "North America", as an example. Currently this is done via (many) workflows (for over 200 countries, INCLUDING all their misspelled/alternate texts). Our many lead sources are NOT consistent of course. Having this in a custom object makes sense. I'm just missing the actually "does Lead.Countrylist_c exist inside CountryLists.Country_c? IF SO, do this, IF NOT, do that." :-/

SOLUTION CREATED FROM HELP GIVEN BELOW:

trigger Country_List_Lookup_LEADS on Lead (before insert,before update) {

    Set<String> countryNames = new Set<String>();

    for( Lead l : trigger.new ) {
        if( l.CountryList__c != null) {
            countryNames.add( l.CountryList__c );
        }
    }

    // Now we have a set of unique country names we want to verify, time to look them up.
    // I plan to build a map of the "match field" -> "full reference object"

    Map<String, Country_List_Reference__c> validCountries = new Map<String, Country_List_Reference__c>();

    for( Country_List_Reference__c obj : [SELECT  Id, 
                                        MTI_Region__c,
                                        Country__c 
                                            FROM    Country_List_Reference__c 
                                            WHERE     Country__c IN :countryNames] ) {
        validCountries.put( obj.Country__c, obj );
    }

    // We have all the reference data we need, last loop on the each lead

    for( Lead l : trigger.new ) {

        if( l.CountryList__c != null ) { // there IS a countrylist entry to deal with... so...

            if( validCountries.containsKey(l.CountryList__c) ) { // found it, do your stuff
                l.Region__c = validCountries.get(l.CountryList__c).MTI_Region__c;

            } else { // do stuff when NOT found
                l.Region__c = '{UNKNOWN COUNTRY LIST ENTRY)';

            }
        } else { // there IS NOT a countrylist entry to deal with...
            l.Region__c = '(COUNTRY LIST IS EMPTY)';
        }

    }


}

I will be expanding the IF...ELSE section at the bottom, but this got the job done. Special thanks to @EyeScream and those who offered their input as well. ;-)

Answer 1

Assuming the Country_List_field__c field on the lead is a freetext, something like this should do.

Note: I've picked stupid names to distinguish between the field on the Lead (Country_List_field__c) and the reference object you want to check it against (Country_List_object__c). Not verified for syntax errors too, just a rough nudge in hopefully right direction.

Set<String> countryNames = new Set<String>();
for(Lead l : trigger.new){
    if(l.Country_List_field__c != null){
        countryNames.add(l.Country_List_field__c);
    }
}

// Now we have a set of unique country names we want to verify, time to look them up.
// I plan to build a map of the "match field" -> "full reference object"
Map<String, Country_List_object__c> validCountries = new Map<String, Country_List_object__c>();
for(Country_List_object__c obj : [SELECT Id, Region__c, Country__c FROM Country_List_object__c WHERE Country__c IN :countryNames]){
    validCountries.put(obj.Country__c, obj);
}

// We have all the reference data we need, last loop on the each lead
for(Lead l : trigger.new){
    if(l.Region__c == null && l.Country_List_field__c != null && validCountries.containsKey(l.Country_List_field__c)){
        // found it, do your stuff
        System.debug(l.Country_List_field__c + ' matched ' + validCountries.get(l.Country_List_field__c));
        l.Region__c = validCountries.get(l.Country_List_field__c).Region__c;
    }
}

Couple of notes:

1. The Country__c field should be unique or the way I'm putting stuff into Map will keep overwriting every time it finds same value.
2. I'd still point you in the direction mentioned by Daniel Hoest. Validation rule with a VLOOKUP + any workflow that would fire afterwards you're 100% sure has fired only on the Leads that passed the validation.
3. Depending on whether you need data from your reference object or just need to know whether a match is found - you can use another Set instead of my map. Minor performance benefit I guess. If it's just Region__c -> you could make a Map<String, String> instead of full objects (use map.put(obj.Country__c, obj.Region__c);
4. Make it a before insert trigger like techtrekker has shown, that way you'll get the database commit for free.

Answer 2

If you don't have any strong motivations for using a custom object, using a custom setting would make your job even easier. If you declared CountryLists as a custom setting (with Country as the Name) rather than object, you could use this (no soql query needed) to lookup the Region Code and any other values.

(After you've added clarifications then your requirements seem to make it quite a good for the use of a CustomSetting, because you're looking up values.)

Trigger LeadBefore on Lead (before insert, before update){


    For (Lead ld : trigger.new)
    If (ld.CountryList__c != null CountryCustomSetting__c.getInstance(ld.CountyList__c) !=  null){
      ld.Region__c = ContryCustomSetting__.getInstance(ld.CountryList__c).Region__c;
    }

 }