Document not uploading to notes and attachments from VF page

Question

I have a VF page where the user is to upload a file and a custom controller to save this to the notes and attachments section of the object record.

I'm receiving the following error when hitting the save button on my VF page:

Insert failed. First exception on row 0 with id a014W00000xc8aOQAQ; first error: INVALID_FIELD_FOR_INSERT_UPDATE, cannot specify Id in an insert call: [Id]
Error is in expression '{!saveScholarship}' in component <apex:commandButton> in page testpage: Class.regularController.saveScholarship: line 14, column 1

Records save successfully when not attaching a document.

Here is my code:

Custom controller

public with sharing class regularController {
    
    public Scholarship_Award__c sch {get;set;}
    public Recipient__c rec {get;set;}
    
    //Constructor
    public regularController(){
    sch = new Scholarship_Award__c();
    rec = new Recipient__c();
    }
    
    public void saveScholarship(){
    rec.School__c=sch.School__c;
    insert rec;
    sch.Recipient__c = rec.Id;  
    insert sch;
    }
}

Controller extension for document upload

public with sharing class testController{
    //
    public testController(regularController ctrlParam){
        
    }
    
       public Recipient__c myCustomObject;
    private Attachment myDocument;
    public Attachment myDoc
    {
        get
        {
            if(myDocument==null){
                myDocument = new Attachment();
            }
            return myDocument;
        }
        set;
    }
    
    public testController(ApexPages.StandardController controller)
    {
        myCustomObject = (Recipient__c) controller.getRecord();
    }
    
    public PageReference upload()
    {
        myDoc.parentId = myCustomObject.Id;
        insert myDoc;
        return null;
    }
}

VF Page

<apex:page controller="regularController" extensions="testController" lightningStylesheets="true">
    <apex:form>
    <apex:pageBlock >
        <!--Recipient form-->
    <apex:pageBlockSection title="Add recipients" columns="2">
        <apex:inputField value="{!rec.Name}"/>
        <apex:inputField value="{!rec.Last_Name__c}"/>
        <apex:inputField value="{!rec.Preferred_Name__c}"/>
        <apex:inputField value="{!rec.Email__c}"/>
        <apex:inputField value="{!sch.Award__c}"/>
        <apex:inputField value="{!sch.School__c}"/>
        <apex:inputField value="{!rec.School__c}" rendered="false"/>
        <apex:inputField value="{!sch.Year__c}"/>
        <apex:inputField value="{!rec.Specialty__c}"/>
    </apex:pageBlockSection>
        <apex:pageBlockSection title="Biography">
        <apex:outputLabel >Upload or enter student biography/CV</apex:outputLabel>
        <apex:inputFile id="myFile" value="{!myDoc.Body}" fileName="{!myDoc.Name}">
        </apex:inputFile>
            <apex:inputTextarea value="{!rec.Biography__c}" rows="3" cols="100"/>
    </apex:pageBlockSection>
        
    <!--Record list-->     
    
        
    <!--Submit all records in record list-->
    <apex:pageBlockButtons location="bottom">
        <apex:commandButton action="{!saveScholarship}" value="Submit"/>
    </apex:pageBlockButtons>
    </apex:pageBlock>
    </apex:form>    
    <apex:pageMessages>
    </apex:pageMessages>
</apex:page>

Thank you all for your help.

Answer 1

If somebody clicks the upload button twice, you wouldn't have gone through the constructor twice. That causes you to try and insert a record that was already inserted.

Change your insert statements to upsert statements in saveScolarship to avoid the problem. That way, the second (and subsequent) clicks won't create new records.

PS: Not sure why you're using an extension with a custom controller. It's significantly easier and straightforward to simply extend your custom controller. Extensions are useful when using a standard controller, which you're not using.