Assign NSInteger Property in iPhone Application

I have a table in SQLite. I want to insert data into this table. The table has response_id, member_id, answer_text, answer_option_update_date_time. response_id and member_id are integers. When I assign any thing to member_id, it gives an error, the object cannot set the property.

@interface Coffee : NSObject {

NSInteger coffeeID;
NSInteger participant_Id;

NSString*question_Id;
NSString*answer_option;
NSString*answer_text;
NSString*update_date_time;




//Intrnal variables to keep track of the state of the object.
}

@property (nonatomic, readonly) NSInteger coffeeID;
@property (nonatomic, retain) NSInteger participant_Id;

@property (nonatomic, copy) NSString *question_Id;
@property (nonatomic, copy) NSString *answer_option;
@property (nonatomic, copy) NSString *answer_text;
@property (nonatomic, copy) NSString *update_date_time;


- (void)save_Local {
    CereniaAppDelegate *appDelegate = (CereniaAppDelegate *)[[UIApplication sharedApplication] delegate];

    Coffee *coffeeObj = [[Coffee alloc] initWithPrimaryKey:0];

    coffeeObj.participant_Id=mynumber;

    NSString*question="1";
    coffeeObj.question_Id=question;
    coffeeObj.answer_option=selectionAnswerOption;
    coffeeObj.answer_text=professionTextField.text;




    NSDate* date = [NSDate date];
    NSDateFormatter* formatter = [[NSDateFormatter alloc] init];
    [formatter setDateFormat:@"yyyy-MM-dd HH:MM:SS"];
    NSString* str = [formatter stringFromDate:date];

    UPDATE_DATE_TIME=str;


    coffeeObj.update_date_time=UPDATE_DATE_TIME;

    //Add the object
    [appDelegate addCoffee:coffeeObj];  
}

When I assign member_id, it gives an error.