EF5 Code First迁移中的程序化数据转换 [英] Programmatic data transformation in EF5 Code First migration
问题描述
是否可以在Entity Framework 5 Code First迁移中进行任何类型的程序化数据转换？
Is it possible to do any type of programmatic data transformation in Entity Framework 5 Code First migrations?
有一个 Sql （）执行查询的方法，但是它的返回类型为void，并且我看不到任何获取执行的查询结果的方法。
There is an Sql() method to execute queries, but it has return type void and I don't see any way to get the results of the queries I perform.
示例
我有表 Recipe 与 Ingredient 有一对多关系。由于各种原因，我想将其转换为Ingredients JSON字符串属性。我能想到的唯一方法是这样的：
I have table Recipe with one-to-many relationship to Ingredient. For various reasons I want to convert this to a Ingredients JSON string property instead. The only approach I can think of is something like this:
- 创建新列 IngredientsJson
- 对于每个食谱，查询其成分，以编程方式构造JSON字符串，然后插入新列中。
- 将旧表 Ingredient 放下。
- Create new column IngredientsJson
- For each recipe, query its ingredients, construct a JSON string programmatically and insert into the new column.
- Drop the old table Ingredient.
推荐答案
您应将db'initializer'用于所需的内容-和/或'Seed （关于在哪里注入EF流）。
You should use db 'initializer' for what you want - and/ore 'Seed' of a sort (as to where to inject into the EF flow).
您可以>使用自定义的< 初始化器-来执行此操作，两者均由Db创建。 。and Migrate 。它不是剪切和粘贴的解决方案，但大多数情况下都可以使用（这是个快速解决问题的方法，您需要稍作调整，下面有一些修复程序）。
You can > take a look at this post with a customized < initializer - that performas both Db Create... and Migrate. It's not cut and paste solution, but mostly works (it was just a fast go at the problem, you'd need to adjust a bit, it has couple fixes below).
MigrateDatabaseToLatestVersion 仅分配迁移部分-您需要种子-暴露-或手动包裹该部分（要点是针对不同情况进行检查-即何时参与迁移-或播种）。
MigrateDatabaseToLatestVersion dose only the migration part - and you need seed-ing exposed - or manually wrap that part (the main point is in 'checks' done for different situations - i.e. when to 'engage' into migration - or seeding).
应该先进行迁移，而除了种子播种外，db creation的意义不大。
Migration should go first, and db 'creation' kind of doesn't make much sense, except for seeding.
您覆盖了种子（您创建的）以将所有数据库处理放在那里-您拥有 DbContext 公开-并且，如果需要，您还可以调用 SqlQuery 。
You override Seed (you created) to put any db handling there - you have the DbContext exposed - and you can also call SqlQuery if needed.
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