小结#
Summary
在本章中，我们继续实现了 ShapeEditor，通过添加三个重要功能：列表视图，以及导入和导出 shapefile 的功能。虽然这些功能看起来不是很激动人心，但它们是 ShapeEditor 的核心组成部分。
在实现这些功能的过程中，我们学到了以下几点：
使用 Django 的模板语言在网页中显示记录列表。
使用 Python 的 zipfile 标准库模块解压上传的 shapefile 的内容，然后使用 OGR 打开该 shapefile。
在将 shapefile 数据导入到 PostGIS 数据库时，您需要“包装”多边形 (Polygon) 和线条 (LineString) 几何图形，以避免 shapefile 无法区分多边形和多重多边形 (MultiPolygon)，以及线条和多重线条 (MultiLineString) 的问题。
当调用对象的 delete() 方法时，Django 会自动删除所有相关的记录，这简化了删除记录及其所有关联数据的过程。
您可以使用 OGR 创建新的 shapefile，并使用 zipfile 库模块将其压缩，以便通过 Web 界面导出地理空间数据。
随着这些功能的实现完成，我们现在可以将注意力转向 ShapeEditor 最有趣的部分：显示并让用户使用平滑地图接口编辑几何图形的代码。这将是本书最后一章的主要内容。
In this chapter, we continued our implementation of the ShapeEditor by adding three important functions: the “list” view, and the ability to import and export shapefiles. While these aren’t very exciting features, they are a crucial part of the ShapeEditor.
In the process of implementing these features, we have learned the following:
Using Django’s templating language to display a list of records within a web page.
Using the zipfile standard library module to extract the contents of an uploaded shapefile before opening that shapefile using OGR.
You will need to “wrap” Polygon and LineString geometries when importing data from a shapefile into a PostGIS database, to avoid problems caused by a shapefile’s inability to distinguish between Polygons and MultiPolygons, and between LineStrings and MultiLineStrings.
When you call the object.delete() method, Django automatically deletes all the linked records for you, simplifying the process of removing a record and all its associated data.
You can use OGR to create a new shapefile, and the zipfile library module to compress it, so that you can export geospatial data using a web interface.
With this functionality out of the way, we can now turn our attention to the most interesting parts of the ShapeEditor: the code that displays and lets the user edit geometries using a slippy map interface. This will be the main focus for the final chapter of this book.