Why am I getting this error:
Catchable fatal error: Object of class Card could not be converted to string in /f5/debate/public/Card.php on line 79
I think one of the object doesn't have toString() method defined so it cannot be represented as string.
Read about string parsing, you have to enclose the variables with brackets {}:
$query = "INSERT INTO cards VALUES('$this->type','$this->tag','{$this->author->last}',"
Whenever you want to access multidimensional arrays or properties of a property in string, you have to enclose this access with {}. Otherwise PHP will only parse the variable up to the first [i] or ->property.
So with "$this->author->last" instead of "{$this->author->last}", PHP will only parse and evaluate $this->author which gives you the error as author is an object.
I don't think you need the $ sign when using arrow operator.
You probably want to use:
$query = "INSERT INTO cards VALUES('$this->type','$this->tag' // etc
You are trying to echo an object itself, not a string property of it. Check your code carefully.
you shouldn't put $ before property names when you access them:
public function insert() {
$mysql = new DB(debate);
$this->initializeInsert();
$query = "INSERT INTO cards VALUES('$this->type','$this->tag','$this->author->last','$this->author->first','$this-$author->qualifications','$this->date->year','$this->date->month','$this->date->day','$this->title', '$this->source', '$this->text')";
$mysql->execute($query);
}