5.9 Table association operations

JFinal ActiveRecord naturally supports table association operations and doesn't need to learn anything new. Table There are two main ways to associate: one is to use sql directly to get the associated data, and the other is to add a method in model to get the associated data.

Suppose you have two existing database tables: user, blog, and user-to-blog is a one-to-many relationship, and the blog table user_id to the user table. The following code demonstrates the first way to get user_name:

public void relation() {
String sql = "select b.*, u.user_name from blog b inner join user u on b.user_id=u.id where b.id=?";
Blog blog = Blog. dao .findFirst(sql, 123); String name = blog.getStr("user_name");
}

public class Blog extends Model<Blog>{
public static final Blog dao = new Blog();

public User getUser() {
return U ser. dao .findById(get("user_id"));
}
}
public class User extends Model<User>{
public static final User dao = new User();

public List<Blog> getBlogs() {
return B log. dao .find("select * from blog where user_id=?", get("id"));
}
}