Your database class has a couple of convenience methods.
您的数据库类有两个较为方便的方法。
Next, write a conventional database class that you will then modify to become dynamic.
接下来，编写一个常规的数据库类，然后再把它修改成动态的。
We made our database a singleton in order to limit the database class to only one instance.
我们将数据库当作一个单实例对象，以将database类限制为1个实例。
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