List has no rows for assignment to SObject - Controller Extension

Question

I've spent several hours today trying to figure this out and running through several online resources here and SFDC forums to no avail.

I keep getting the following error:

List has no rows for assignment to SObject An unexpected error has occurred. Your development organization has been notified.

Here is my code:

public class SubscriptionAddProdExtension {

    private Final Subscription__c sub;

    public ApexPages.StandardController thisAddProdController {get; set;}
    public Subscription_Additional_Products__c sAddProd {get; set;}

    public ApexPages.StandardController standardContactController;

    public SubscriptionAddProdExtension(ApexPages.StandardController cntrl) { 

        this.sub = (Subscription__c)cntrl.getRecord();

        List<Subscription_Additional_Products__c> sap = [SELECT Name, Id, Expiry_Date__c, Subscription__c, Tax_Type__c, Name__c FROM Subscription_Additional_Products__c WHERE Subscription__c =:this.sub.Id];
        if(sap.size() >0 ){
            system.debug('Retrieved Subscription_Additional_Products__c ' + SAddProd.id);
            return;
        }
        if(sap.size() == null ){
            system.debug('Retrieved Subscription_Additional_Products__c ' + SAddProd.id);
            return;
        }
        else{

        sAddProd = [SELECT Name, Id, Expiry_Date__c, Subscription__c, Tax_Type__c, Name__c
        FROM Subscription_Additional_Products__c WHERE Subscription__c = :this.sub.Id ];
        system.debug('Displaying ' + SAddProd.id);

        thisAddProdController = new ApexPages.StandardController(sAddProd);
        }
    }
        public pageReference doSaveAll() {
            standardContactController.save();
            thisAddProdController.save();
            return null;
        }
}

VisualForce Markup:

<apex:pageBlock title="Aditional Products" mode="edit" >
    <apex:pageBlockButtons>
        <apex:commandButton action="{!save}" value="Save"/>
    </apex:pageBlockButtons>
    <apex:pageBlockSection title="Product Details" columns="2" >
        <apex:outputField value="{!sAddProd.Name}"/>
        <apex:outputField value="{!sAddProd.Tax_Type__c}"/>
        <apex:outputField value="{!sAddProd.Expiry_Date__c}"/>
        <apex:outputField value="{!sAddProd.Name__c}"/>
    </apex:pageBlockSection>
</apex:pageBlock>

Answer 1

You should just use cntrl.getId() instead. Calling cntrl.getRecord() only pulls in the fields included on your page. Everywhere you have this.sub.Id, change it to cntrl.getId().

That said, you are never guaranteed to have a child record. The standard approach to querying for a single record whose existence is not guaranteed is to query to a list, then check if it is empty:

List<ChildObject__c> candidates = [
    SELECT ... FROM ChildObject__c
    WHERE Parent__c = :controller.getId()
    LIMIT 1
];
if (!candidates.isEmpty())
    childRecord = candidates[0];