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我在 Rails 3 上有一个带有 PostgreSQL 数据库的应用程序。

问题是：我想用 object_id 存储坐标来访问它，例如：

Post1 -> Coordinates [100,200] -> Attachment1
Post1 -> Coordinates [400,400] -> Attachment2
Post1 -> Coordinates [200,500] -> Attachment3

Post2 -> Coordinates [150,310] -> Attachment1

Post3 -> Coordinates [50,710] -> Attachment1
Post1 -> Coordinates [430,430] -> Attachment2

我想将所有附件存储在一个地方（即协调模型），以免使事情变得混乱。是否可以？

我从未遇到过任何解决此问题或类似问题的方法。

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1 回答 1

4

这看起来像一个简单的 m:n 关系，具有两部分键。使用联合表对其进行建模。(post, attachment)为了给你这个想法，假设每个坐标位置只能有一对，SQL 措辞将是：

CREATE TABLE post (
    post_id serial primary key,
    blah_other_data text
);

CREATE TABLE attachment (
    attachment_id serial primary key,
    blah_other_data text
);

CREATE TABLE post_attachment (
    post_id integer not null REFERENCES post(post_id),
    attachment_id integer not null REFERENCES attachment(attachment_id), 
    coordinate_x integer not null,
    coordinate_y integer not null,
    PRIMARY KEY (coordinate_x, coordinate_y)
);

我相信您可以将其转换回 Rails 模型和查询。

(post,attachment)如果每个坐标位置可以有多个对，那么您必须通过将坐标列添加到键来调整PRIMARY KEYof以允许这样做。post_attachments

演示数据设置：

INSERT INTO post (blah_other_data)
VALUES ('Post1'),('Post2'),('Post3');

INSERT INTO attachment(blah_other_data)
VALUES ('Attachment1'),('Attachment2'),('Attachment3');

INSERT INTO post_attachment (post_id, attachment_id, coordinate_x, coordinate_y)
SELECT post_id, attachment_id, x, y
FROM (VALUES
    ('Post1', 100,200, 'Attachment1'),
    ('Post1', 400,400, 'Attachment2'),
    ('Post1', 200,500, 'Attachment3'),
    ('Post2', 150,310, 'Attachment1'),
    ('Post3', 50,710,  'Attachment1'),
    ('Post1', 430,430, 'Attachment2')
) rows(post_data,x,y,attachment_data)
INNER JOIN post ON (post.blah_other_data = rows.post_data)
INNER JOIN attachment ON (attachment.blah_other_data = rows.attachment_data);

使用连接访问数据：

SELECT p.post_id, p.blah_other_data AS post_data, 
       a.attachment_id, a.blah_other_data AS attachment_data, 
       c.coordinate_x, c.coordinate_y 
FROM post_attachment c 
INNER JOIN post p ON (c.post_id = p.post_id) 
INNER JOIN attachment a ON (c.attachment_id = a.attachment_id);
 post_id | post_data | attachment_id | attachment_data | coordinate_x | coordinate_y 
---------+-----------+---------------+-----------------+--------------+--------------
       3 | Post3     |             1 | Attachment1     |           50 |          710
       2 | Post2     |             1 | Attachment1     |          150 |          310
       1 | Post1     |             1 | Attachment1     |          100 |          200
       1 | Post1     |             2 | Attachment2     |          400 |          400
       1 | Post1     |             2 | Attachment2     |          430 |          430
       1 | Post1     |             3 | Attachment3     |          200 |          500
(6 rows)
于 2012-11-19T01:39:33.973 回答