[SalesForce] How to create Opportunity Validation Rules without breaking Lead Conversion

Put your DML statement inside the "Try" section of a Try Catch block and then handle the DML error like this:

List<Custom__c> trgCusts; // this is the list you are trying to perform DML on

try {
    update trgCusts;
}
catch (DMLException e) {
    for (Custom2__c cust2 : trigger.new) {
        cust2.addError(e.getDmlMessage(0));
    }
}
catch (Exception e) {
    for (Custom2__c cust2 : trigger.new) {
        cust2.addError(e.getMessage());
    }
}

Be aware that this will fail every record in the trigger batch with the first record's error message - possibly desirable but if not you can use the Database.update() method to receive detailed information about which records fail and then map these back to the trigger records and only fail those that you want to.

Update

trigger primaryLiaisonCount2 on Contact(after update) {
    if(checkRecursive.runOnce()){
        List<Account> accList = new List<account>();
        List<Account> accListToUpdate = new List<account>();
        Set<Account> accSet = new Set<Account>();
        set<id> allAccIds = new Set<id>();    

        for (Contact c1: trigger.new){
            //excluding Marketo, Ken Reyes, and Arnold one line below.
            if (c1.AccountID != null && c1.LastModifiedById != '00500000006wnoE' && c1.LastModifiedById != '00500000006xdMm' && c1.LastModifiedById != '00500000006wsIm'){
            allAccIds.add(c1.AccountID);
            } 
        }


        decimal amount1=[SELECT count() FROM Contact WHERE AccountID IN :allAccIds AND Primary_Liaison__c != null AND Marketing_Status__c != 'Gone From Company'];
        decimal amount2=[SELECT count() FROM Contact WHERE AccountID IN :allAccIds AND Receive_Client_Survey__c = true AND Marketing_Status__c != 'Gone From Company'];
        LIST<Account> acc1=[SELECT ID FROM Account WHERE ID IN :allAccIds AND recordtypeID = '012000000000j8S'];
        list<Account> acc3=[SELECT ID From Account WHERE ID NOT IN :allAccIds AND recordtypeID ='012000000000j8S'];

        for (Contact c1: trigger.new){
            for (Account acc2:acc1){
                acc2.Primary_Liaisons__c = amount1;
                acc2.Receive_Client_Surveys__c = amount2;
                accList.add(acc2);           
            }
        }

        accSet.addall(accList);
        accListToUpdate.addall(accSet);

        try {
            update accListToUpdate;
        }
        catch (DMLException e) {
            for (Contact con : trigger.new) {
                con.addError(e.getDmlMessage(0));
            }
        }
        catch (Exception e) {
            for (Contact con : trigger.new) {
                con.addError(e.getMessage());
            }
        }
    }

}

The code inside each Catch block will only run if that type of Exception is thrown - so only one Catch block will ever run. That's why the fact they are both called "e" doesn't matter.

When performing DML if an exception occurs (e.g. validation rule) then a DMLException will be thrown which has a special method on it called getDmlMessage(). The other catch block (catch (Exception e)) is optional you can remove it seeing as you are only doing DML in the Try section.

The problem looks clear to me as you are facing a challenge with the small point in order of execution of salesforce.

To understand this you need to refer to order of execution in salesforce.

Triggers and Order of Execution

If you go to the link you'll find out in step 4 the custom validations are run once again after the before triggers which fails your logic.

STEP 4: Runs most system validation steps again, such as verifying that all required fields have a non-null value, and runs any user-defined validation rules. The only system validation that Salesforce doesn't run a second time (when the request comes from a standard UI edit page) is the enforcement of layout-specific rules.

To avoid the problem I would request you to not make the checkbox BypassCloseddateValRule, you created to bypass the validation rule to FALSE in the trigger.

You should do this change in a later step after which custom validations are not called, i.e. in STEP 7 (After Trigger) or STEP 11 (Workflow field Update).

Because custom validation rules will not be called after those steps.

STEP 12: If the record was updated with workflow field updates, fires before update triggers and after update triggers one more time (and only one more time), in addition to standard validations. Custom validation rules and duplicate rules are not run again.

I believe this will solve your problem. Let us know if you face any other challenge.

Thank You.