如何在 Java 中为面向对象的元模型编写 SQL 查询代码

Question

我正在尝试学习如何使用名为 Eyedb（在 linux 上）的工具来创建面向对象的模型数据库。我已经为这个数据库制作了一些类和记录生成器，但我不知道如何使用 Java 编写查询代码。

数据库的结构如下：

    class Lecturer {

        attribute string<32> name;
        attribute strin<32> surname;
        relationship set <Lecture*> lectures inverse Lecture::Lecturer;
};

class Item{
        attribute string<32> name;
        attribute string<512> description;
};

class Topic extends Item {
        relationship set<Lecture*> tlecture inverse Lecture::Topic;
};


class Lecture {
        relationship Lecturer *llecturer inverse Lecturer::lectures;
        relationship Topic *ltopic inverse Topic::tlecture;
        relationship set <Content*> lcontent inverse Content::Lecture;
        relationship set <Equipment*> lequipment inverse Content::Lecture;
        relationship Room_timeslot* lroom_timeslot inverse Room_timeslot::rlecture;                                                     
};

class Content extends Item {

        attribute int level;
        relationship set <Content*> subcontent inverse Content::supcontent; 
        relationship set <Content*> supcontent inverse  Content::subcontent;    
        relationship set <Teachingmaterial*> cteachingmaterial inverse Teachingmaterial::Content;
};

class Teachingmaterial extends Item {

        attribute string link;
        relationship set <Content*> tcontent inverse Content::Teachingmaterial;
};

class Equipment extends Item {
        attribute int quantity;
        attribute string symbol;
        relationship set<Lecture*> electure inverse Lecture::Equipment;
        relationship Room *eroom inverse Room::requipment;

};

class Room {
        relationship set <Equipment*> requipment inverse Equipment::Room
        attribute string name;
        attribute int number;
        attribute string symbol;
        attribute string building;
        attribute int floor;
        attribute string wing;
        relationship set <Room_timeslot*> rroom_timeslot inverse Room_timeslot::Room;
};

class Room_timeslot {
        relationship Room *room inverse room::rroom_timeslot;
        relationship Lecture* rlecture inverse Lecture::Room_timeslot;
        relationship set <Timeslot*> rtimeslot inverse Timeslot::lroom_timeslot;
};

class Timeslot {
        attribute string name;
        attribute int number;
        attribute time timemargin_start;
        attribute time timemargin_end;
        relationship set <Room_timeslot*> troom_timeslot inverse Room_timeslot::rtimeslot;
};

我想进行如下所示的查询：

SELECT lr.name as lecturer, t.name as topic FROM topic t        
JOIN lecture l ON t.id_topic = l.id_topic
JOIN lecturer lr ON lr.id_lecturer = l.id_lecturer
ORDER BY lr.name

select t.name as topic from topic t 
join lecture l on t.id_topic = l.id_topic 
join lecturer lr on lr.id_lecturer = l.id_lecturer
where lr.name = "name1"

SELECT tm.name as teaching_material, e.name as equipment, lr.name as lecturer FROM teachingmaterial tm
JOIN teaching_content tc ON tc.id_teachingmaterial = tm.id_teachingmaterial
JOIN content c ON c.id_content = tc.id_content
JOIN content_lecture cl ON cl.id_content = c.id_content
JOIN lecture l ON l.id_lecture = cl.id_lecture
JOIN lecture_equipment le ON le.id_lecture = l.id_lecture
JOIN equipment e ON e.id_equipment = le.id_equipment
JOIN lecturer lr ON lr.id_lecturer = l.id_lecturer

Answer 1

Java 使用 JDBC 与关系数据库进行通信。如果您的数据库有 JDBC 驱动程序，那么一切就绪。如果没有，那你就不走运了。 SQL Server 和 MySQL 都有 JDBC 驱动程序，所以它们应该不是问题。你需要这些和JDBC tutorial。

看起来EyeDB 是一个我从未听说过的对象数据库。它声称可以被 C++ 和 Java 使用。

我希望至少有一个“hello world”连接示例。我怀疑任何甚至无法正确获取其网页上的 HTML 的软件。

有Java documentation 可用。看起来很糟糕。这是一个要求吗？有更好的数据库，包括关系（MySQL、SQLLite 或 PostgreSQL）、对象（例如JODB）或图形（NEO4J）。一定要用这个吗？

EyeDB 文档清楚地说明了这些步骤。 sample problem：

1. 使用 EyeDB 对象定义语言 (ODL) 定义架构
2. 使用您下载的 EyeDB eyedbodl 工具从架构中生成 Java 类。
3. 使用生成的与数据库交互的类编写客户端程序。

一切都在那里。试试看吧。