从一个django模型迁移到使用外键引用的两个模型 [英] Migrate from one django model to two models referenced with a foreign key

问题描述

我需要在以下Django模型中外包一些属性：

I need to outsource some of the attribues in the following Django model:

class TextResult(models.Model):
    user = models.ForeignKey(settings.AUTH_USER_MODEL, default=1)
    text = models.ForeignKey(Text)
    # following fields will be in the referenced model
    wpm = models.FloatField(default=0.0)
    accuracy = models.FloatField(default=1.0,
                                 validators=[MinValueValidator(0.0),
                                             MaxValueValidator(1.0)])

提到具体数据的模型：

class TextResult(models.Model):
    user = models.ForeignKey(settings.AUTH_USER_MODEL, default=1)
    text = models.ForeignKey(Text)
    typing_result = models.ForeignKey(TypingResult)

class TypingResult(models.Model):
    wpm = models.FloatField(default=0.0)
    accuracy = models.FloatField(default=1.0,
                                 validators=[MinValueValidator(0.0),
                                             MaxValueValidator(1.0)])

问题是数据库中已经有一些数据，所以我必须将数据迁移到新的结构，什么是最简单，最干净的方法来实现？

The problem is, that there is already some data in the database, so I have to migrate the data to the new structure, what is the easiest, cleanest way to achieve that?

推荐答案

我将进行三步迁移。

1. 创建新字段

1. Create the new fields

1.1。创建 TypingResult 模型和 typing_result = models.ForeignKey（TypingResult，blank = True，null = True）字段。确保FK是可选的，使其为空白且无效

1.1. Create TypingResult model and the typing_result = models.ForeignKey(TypingResult, blank=True, null=True) field. Make sure the FK is optional by making it blank-able and null-able

1.2通过迁移检查点

1.2 Checkpoint by migrating

1. 数据迁移

1. Data Migration

2.1使用本指南 https://docs.djangoproject.com/en/1.11 / topics / migrations /＃data-migrations ，并添加数据迁移说明。

2.1 Create an empty migration using this guide https://docs.djangoproject.com/en/1.11/topics/migrations/#data-migrations and add instructions for data migrations.

2.2数据迁移步骤如下：

2.2 The data migration steps are as follows:

• 迭代通过所有 TextResult 为每个人创建一个 TypingResult 与相应的数据

• Iterate through all TextResult for each of them create a TypingResult with the corresponding data

通过FK将 TypingResult 链接到 TextResult

2.3运行迁移到检查点

2.3 Run the migration to checkpoint

1. 清理

1. Cleanup

3.1删除 TextResult 并使ForeignKey不可选。

3.1 Delete the wpm and accuracy fields on the TextResult and make the ForeignKey non-optional.

3.2运行迁移

结论

这可能全部在1个步骤中完成，但最好是了解发生了什么。另外在 .save（）调用之前添加pdb将允许您检查数据迁移的步骤

This can probably all be done in 1 step, but it's best to understand what is going on. Also adding pdb before a .save() call will allow you to inspect the steps for the data migration

import pdb; pdb.set_trace()

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