家庭作业 | AppMaster

{ "en": "/course-library/crash-course-101/crash-course-module8-homework", "fr": "/fr/course-library/crash-course-101/crash-course-module8-homework-fr", "es": "/es/course-library/crash-course-101/curso-intensivo-modulo8-deberes", "de": "/de/course-library/crash-course-101/crashkurs-modul8-hausaufgaben", "ru": "/ru/course-library/crash-course-101/domashnee-zadanie-crash-course-module8", "ja": "/ja/course-library/crash-course-101/kuratsushiyukosumodule8-su-ti", "ko": "/ko/course-library/crash-course-101/dangijibjunggwajeong-modyul8-sugje", "zh": "/zh/course-library/crash-course-101/beng-kui-ke-cheng-mo-kuai-8de-zuo-ye", "pt": "/pt/course-library/crash-course-101/modulo-de-curso-intensivo8-trabalho-de-casa", "hi": "/hi/course-library/crash-course-101/kraish-kors-monddyuul8-homvrk", "bn": "/bn/course-library/crash-course-101/kryaash-kors-mddiul8-homoy-aark", "ar": "/ar/course-library/crash-course-101/whd-dwr-mkthf-8-wjb-mnzly", "id": "/id/course-library/crash-course-101/modul-kursus-kilat8-pekerjaan-rumah", "tr": "/tr/course-library/crash-course-101/hizlandirilmis-kurs-modulu8-odevi", "it": "/it/course-library/crash-course-101/corso-intensivo-modulo-8-compiti-a-casa", "pl": "/pl/course-library/crash-course-101/crash-course-modul8-zadanie-domowe", "vi": "/vi/course-library/crash-course-101/khoa-hoc-cap-toc-module8-bai-tap-ve-nha", "nl": "/nl/course-library/crash-course-101/spoedcursus-module8-huiswerk", "th": "/th/course-library/crash-course-101/khwaamphidphlaadkh-nghlaksuutromduul-8-kaarbaan" }

完善后台的数据模型和业务流程，使城市的人口信息以千人为单位计算，并以 "XX，XXX "的格式显示（同时，数据库中会存储精确到一人的总人数）。
如果没有指定一个城市属于哪个国家的信息，则禁止创建该城市。
显示关于世界的摘要信息。城市总数，人口总数，最大和最小的城市，成立日期未知的城市数量。
添加一个按钮，删除所选国家的所有城市。