Amount change on Opportunity Apex Trigger - triggers

Question

I'm trying to create trigger if record type is Revenue Risk then amount should be saved in negative value, Here's my code in which I'm having error, I tried it two ways, second is in comments.. none of them is working
public with sharing class amountValidator {
//pull data of Opportunity in list
public static void validateAmount (list<Opportunity> oppList){
oppList = [Select amount FROM Opportunity WHERE RecordType.Name IN ('Revenue Risk')];
for(Opportunity opportunities : oppList){
if(oppList.amount >= '0'){
oppList.amount = oppList.amount * '-1';
}
}
/*Map<String,Schema.RecordTypeInfo> rtMapByName = d.getRecordTypeInfosByName();
Schema.RecordTypeInfo rtByName = rtMapByName.get('Revenue Risk');
for(Opportunity each : oppList){
if(rtByName.size == 0){
}
else{
if(oppList.Amount >= 0){
oppList.Amount = oppList.Amount*-1;
}
}
}*/

Answer 1

The error is very clear:
if(oppList.amount >= '0'){ // THIS LINE WILL THROW AN ERROR: 'Comparison arguments must be compatible types: Integer (or Double), String
oppList.amount = oppList.amount * '-1'; // THIS ONE TOO: 'Arithmetic expressions must use numeric arguments'
}
Your second code snippet is also wrong (same for first one).
if(oppList.Amount >= 0){
oppList.Amount = oppList.Amount*-1;
// MUST BE each.Amount = each.Amount * - 1; Please try not to use reserved words as variable names
}
You may want to take a look at a previous post describing strongly typed programming languages: Strongly Typed

Answer 2

Since we can't add comments just yet, we're going to add a new answer:
You're not updating/inserting the updated amount for your opportunity.
The correct way of doing this is to create a separate List of Opportunities (i.e. List oppsToUpdate) and add the updated opportunities to this list.
public static void validateAmount (list<Opportunity> oppList){
oppList = [Select amount FROM Opportunity WHERE RecordType.Name IN ('Revenue Risk')]; // Why are you requerying the Opportunity if you already have it??
List<Opportunity> oppsToUpdate = new List<Opportunity>();
for(Opportunity opportunities : oppList){
if(opportunities.amount > 0){
opportunities.amount = opportunities.amount * -1;
oppsToUpdate.add(opportunities);
}
}
upsert opportunities;
}
Remember to enclose your function with try-catch statements with system debugs to see what's going on with your code.
And this is the link to the input parameter modifications and why this is bad practice: Input Parameters

Answer 3

Working Code:
trigger Risk_NegativeQuantity on OpportunityLineItem (before insert) {
set<id> oppid = new set<id>();
for (OpportunityLineItem oli : trigger.new)
{
oppid.add(oli.opportunityid);
}
Id RevenueRisk= Schema.SObjectType.Opportunity.getRecordTypeInfosByName().get('Revenue Risk').getRecordTypeId();
list<opportunity> opplist = [select id, recordtype.name,recordtypeid from opportunity where id in : oppid ];
for (OpportunityLineItem oli : trigger.new)
{
for (opportunity opp: opplist)
{
if (oli.opportunityid == opp.id)
{
if(opp.recordtype.name == 'Revenue Risk')
{
if(oli.Quantity > 0)
{
oli.Quantity = oli.Quantity * -1;
}
}
}
}
}
}