ruby - DataMapper 连接语句

Question

如何使用 ruby​​ DataMapper 生成带有连接语句的查询？

IE。

class Model1
    property id, Serial
    has n :Model2s, :parent_key => [ :id ], :child_key => [ :model1_id ]
end

class Model2
    property :id, Serial
    property :model1_id, Integer
    has n :Model3s, :parent_key => [ :id ], :child_key => [ :model2_id ]
end

class Model3
    property :id, Serial
    property :model2_id, Integer
end

现在我希望 DataMapper 创建一个查询，如：

SELECT ... FROM model1 INNER JOIN model2 ON model1.id = model2.model1_id INNER JOIN model3 ON model2.id = model3.model2_id;

目前它在访问它们时延迟加载所有关系与单个查询，这非常慢。