How do I use batch apex if my method is creating over 40000 records

Question

It's just a simple question I'm having(It might sound silly but I've no idea how do I insert 40000 records).

I'm first creating 200 Accounts and also creating 200 child Opportunities for each Account. Can Someone suggest to me how do I achieve it?

I think it can be done using BatchApex but I've no idea how to code for that. Below is what I'm trying to do:

public class TestOpp {
    public static void accwithOpp(){
        List<Account> createdAccount = new List<Account>();
        List<Opportunity> createdOopp = new List<Opportunity>();
        for(Integer i=1;i<=200;i++){
            Account a = new Account(Name='TestMebyClass'+i);
            createdAccount.add(a);
        }
        insert createdAccount;
        List<Account> ParentAccIds = [SELECT Id FROM Account WHERE Id IN :createdAccount];
        for(Account a : ParentAccIds){
            for(Integer i=1;i<=200;i++){
                Opportunity op = new Opportunity(Name='TestofParentAcc'+i,
                                                StageName='Prospecting',
                                                CloseDate=System.today().addmonths(1),
                                                AccountId=a.Id);
                createdOopp.add(op);
            }
        }
        insert createdOopp;
    }
}

Answer 1

You can create the counter values as an array and return that from the start method (this being the less commonly used variant of start):

public System.Iterable start(Database.BatchableContext jobId) {

    Integer[] counts = new Integer[] {};
    for(Integer i=1;i<=200;i++) counts.add(i);
    return counts;
}

public void execute(Database.BatchableContext jobId, Integer[] counts) {

    Account[] accs = new Acccount[] {};
    for (Integer count : counts) {
        accs.add(new Account(Name='TestMebyClass'+count));
    }
    insert accs;

    Opportunity[] accs = new Opportunity[] {};
    for(Account a : accs){
        for(Integer i=1;i<=200;i++){
            opps.add(new Opportunity(
                Name='TestofParentAcc'+i,
                StageName='Prospecting',
                CloseDate=System.today().addmonths(1),
                AccountId=a.Id
            ));
        }
    }
    insert opps;
}

public void finish(Database.BatchableContext jobId) {
}

and then use a batch size that stays within governor limits, in this case say 50.