I am getting this error when I go into Edit mode for a record. I'm using the same controller & VF page that I am using for a New record of the same object. 

SObject row was retrieved via SOQL without querying the requested field: Contract_Overview__c.Contract_Start_Date__c 

I thought it would solve the problem to retrieve the field in my query  (such as Name and Contract_Type_c) - but then I just get the same error for the next field which is included as an input field in the VF page. I guess I could solve the whole problem by just retrieving EVERY single field which is an input field in the VF page, but I don't want to have to do that. There's gotta be a better way. 

Here is the controller being used : 

public class MycontrollerSFDCBETA2{

    public String rightOptionsHidden { get; set; }

    public String leftOptionsHidden { get; set; }

    public MycontrollerSFDCBETA2() {

    }

    public Account selectedUser { get; set; }
    String contractid;
    public Contract_Overview__c contract{get;set;}
    public string relatedAccount{get;set;}
    public string names{get;set;}
    public string accountid{get;set;}
    public Name contractnew{get;set;}
    public string selectedaccountid{get;set;}
    public String message { get; set; }

    public List<SelectOption> selectedContacts { get; set; }
    public List<SelectOption> options { get; set; }

    public MycontrollerSFDCBETA2(apexpages.standardcontroller controller)
        {
        selectedContacts = new list<SelectOption>();
        contract = new Contract_Overview__c();
        contractid=system.currentpagereference().getparameters().get('id');
            if(contractid!=null)
            {
                contract=[select account__c,Name,Contract_Type__c,  Subsidiaries_On_Contract__c from Contract_Overview__c  where id =:contractid];
                relatedAccount=Contract.account__C;
            }
        }

    public pageReference  execute()
        {
        accountid=contract.Account__c;
        System.debug('########'+accountid);
        return null;
        }

    public list<selectoption> getitems()
        {
        
        List<selectoption> options= new list<selectoption>();
                    
        if(accountid != null)
            {
                account a =[select name , (select name from Subsidiaries_and_Brands__r) from account where id =:accountid];
        for(SubsidiariesAndBrands__c s : a.Subsidiaries_and_Brands__r)
                    {
                    options.add(new SelectOption(s.name,s.name));
                    }
            }
        else
            options.add(new SelectOption('None','None'));
            return options;
            
        }
            
    public void save()
        {
        
        System.debug('********************************' + names);
        
        message = null ;       
        Boolean first = true;
        for ( SelectOption so : selectedContacts ) {
            if (first) {
                message = message ;
            }
            
                
            message = message + ', ' + so.getValue() ;
            
            first = false;
            
        }
        
        message=message.removeStart('null, ');
        message='['+message+']';
        
        System.debug('********************************' + message);
        contract.Subsidiaries_On_Contract__c=message;
        
        insert contract;
        contract=new Contract_Overview__c  ();
        System.debug('********************************' + contract);
                  
        }
}

and here's part of the VF page : 

<apex:outputLabel value="Contract Overview Name : "/>
                    <apex:inputfield value="{!contract.Name}" />
                    <apex:outputfield value="{!contract.OwnerId}"/>
                    <apex:outputLabel value="Contract Type : "/>
                    <apex:inputfield value="{!contract.Contract_Type__c}" required="false"/><br></br>
                    <apex:outputLabel value="Contract Status : "/>
                    <apex:inputfield value="{!contract.Contract_Status__c}" required="false"/><br></br>
                    <apex:outputLabel value="Contract Start Date : "/>
                    <apex:inputfield value="{!contract.Contract_Start_Date__c}" required="false"/><br></br>

So, in other words, if I retrieve Status__c in the query I'll just get that same sObject error for Contract_Start_Date__c and so on and so on...

I'm sure there's gotta be a better way than this. Anybody know them ? 

Thank you very much for your help.