骨头汤和豆腐哪个更补钙？
动物骨头中的钙很难溶解到汤里，喝骨头汤补钙效果甚微。但每100克豆腐约含有78毫克的钙，钙含量相对更高。
当膳食中钙摄入不足时，可选择纯度高、杂质少、来自天然矿物的碳酸钙补充剂，碳酸钙钙含量高，易被人体吸收，与镁锰锌铜等多种营养素协同作用，促进钙吸收，补钙效果翻倍。同时每天补充10微克维牛素D，巩固钙吸收。
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Django change an existing field to foreign key
I have a Django model that used to look like this:class Car(models.Model): manufacturer_id = models.IntegerField()There is another model called Manufacturer that the id field refers to. However, I realized that it would be useful to use Django's built-in foreign key functionality, so I changed the model to this:class Car(models.Model): manufacturer = models.ForeignKey(Manufacturer)This change appears to work fine immediately, queries work without errors, but when I try to run migrations, Django outputs the following:- Remove field manufacturer_id from car - Add field manufacturer to carDoing this migration would clear all the existing relationships in the database, so I don't want to do that. I don't really want any migrations at all, since queries like Car.objects.get(manufacturer__name="Toyota") work fine. I would like a proper database foreign key constraint, but it's not a high priority.So my question is this: Is there a way to make a migration or something else that allows me to convert an existing field to a foreign key? I cannot use --fake since I need to reliably work across dev, prod, and my coworkers' computers.内容来源于 Stack Overflow, 遵循 CCBY-SA 4.0 许可协议进行翻译与使用。原文链接：Django change an existing field to foreign key
