如何显示烧瓶中数据库中的链接数据？ [英] How to display linked data from database in flask?

问题描述

我的数据库中有一个包含链接列表的表。

I have a table in my database containing a linked list.

ID | page | prior | next
1  | A    | 0     | 2
2  | B    | 1     | 3
3  | C    | 2     | 4
4  | D    | 3     | 5
5  | E    | 4     | 0

如何显示此表中的所有项目？经过几次位置互换和插入操作后， SORT BY 无效。我正在使用Flask，它使用Jinja2模板。我当前的方法是找到第一个项目并将其添加到列表中。然后，根据上一项的下一个值，收集下一行并将其添加到列表中。

How do I display all the items in this table? A SORT BY wouldn't work after a few positional swaps and insertions. I'm using Flask, which uses Jinja2 templates. My current approach is to locate the first item and add it to a list. Then, based on the previous item's "next" value, collect the next row and add it to the list.

num_rows = Pages.query.count()

# find first row, the one where prior is 0
first_row = Pages.query.filter_by(prior=0).first()

# create a list containing just the first row for now
all_rows = [first_row, ]

# add new rows to the list
for i in range(0, (num_rows-1)):
    current_row = all_rows[i].next
    all_rows.append(Pages.query.get(current_row))

最后，我将列表传递给 render_template（'template.html'，all_rows = all_rows），然后检索

Finally, I pass the list to render_template('template.html', all_rows = all_rows), then retrieve it in the template.

肯定有一种更优雅的方法吗？我想这会执行得很糟糕并且需要大量资源吗？

Surely there's a more elegant approach? I imagine that this would perform terribly and require lots of resources?

推荐答案

这取决于您使用的是哪种DBMS。 Oracle具有专有的按优先级连接语法，该语法非常易于阅读。许多其他语言的 WITH 语法较难理解，但可以实现相同的结果。

It depends on what DBMS you’re using. Oracle has a proprietary CONNECT BY PRIOR syntax that’s very easy to read. Many others have a WITH syntax that’s harder to follow but can accomplish the same result.

请参见在SQL SERVER中模拟ORACLE的PRI优先级连接。

这篇关于如何显示烧瓶中数据库中的链接数据？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！