如何使用Java中的SQL对来自对象的元模型的查询进行编码

Question

I'm trying to learn how to create an object oriented model database using a tool called: Eyedb (on linux). I've made some classes and records generators for this database but I don't know how to code queries for it using Java.

The structure of the database looks like this:

    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;
};

I want to make queries that look like this:

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 uses JDBC to communicate with a relational database. If your database has a JDBC driver you're all set. If not, you're out of luck. Both SQL Server and MySQL have JDBC drivers, so they should not be a problem. You'll need those and the JDBC tutorial .

Looks like EyeDB is an object database that I've never heard of. It claims to be usable by C++ and Java.

I'd expect at least one "hello world" connection example. I'm suspicious of any software that doesn't even get the HTML on its web page right.

There's Java documentation available. Looks awful. Is this a requirement? There are better databases, both relational (MySQL, SQLLite, or PostgreSQL), object (eg JODB ), or graph (NEO4J). Must you use this one?

The EyeDB documentation makes the steps clear. They are spelled out for you in the sample problem :

1. Define the schema using the EyeDB Object Definition Language (ODL)
2. Generate the Java classes from the schema using the EyeDB eyedbodl tool, which comes with your download.
3. Write a client program using the generated classes that interact with the database.

It's all there. Give it a try.