从扩展类访问属性

Question

I'm trying to crate a Model structure, to access a database, inspired by Laravel's Eloquent (PHP).

Basically I've got a class called Model , and for now it's just empty.

I then got another class called User , which extends Model

public class User extends Model {

    private String table = "users";
}

As you can see the User class also got a property called table, which refers to the table on the database the model is representing.

Inside of my Model.java I'm then trying to fetch the name of the table.

So far I'm running some code on my Model.java constructor where I go through all of the fields, on the instance. This gives me a Field object, but I'm unable to get the content of table from Model.java

Model.java :

public abstract class Model {

    public Model()
    {
        List<Field> fields = new ArrayList<>();
        for (Class<?> c = this.getClass(); c != null; c = c.getSuperclass()) {
            fields.addAll(Arrays.asList(c.getDeclaredFields()));
        }
        for (Field field : fields)
        {
            String name = field.getName(); //returns "table"
        }
    }
}

All In all, what I need to is to get the table name from the class that's extends model.

Any ideas? or is this a bad practice?

Answer 1

Model should have an abstract method, getTableName

Yes it is bad practice because a class should not know details about class that inherit from it.

The way you are doing it, there's no contract that specifies that a subclass must implement that field.

By creating a method that has to be implemented by subclass, there's a clear contract and you are applying the dependency inversion principle. See https://en.m.wikipedia.org/wiki/Dependency_inversion_principle

public abstract class Model {

    public Model() {}

    abstract String getTableName();
}

public class User extends Model() {
    public String getTableName(){
      return "users";
    }
}