在散列中重命名某个键。

I have a column car_details with 2000 entries, each of which is a hash of info that looks like this:

我有一个包含2000个条目的car_details列，每个条目都是这样的信息散列:

{"capacity"=>"0",
 "wheels"=>"6",
 "weight"=>"3000",
 "engine_type"=>"Diesel",
 "horsepower"=>"350",
 "fuel_capacity"=>"35",
 "fuel_consumption"=>"30"}

Some cars have more details, some have less. I want to rename the "fuel_consumption" key to "mpg" on every car that has that key.

有些车有更多的细节，有些车有更少的细节。我想将“fuel_consumption”键重命名为“mpg”键，用于每辆拥有该键的汽车。

2 个解决方案

#1

As far as I know, there is no easy way to update a serialized column in a data table en masse with raw SQL. The best way I can think of would be to do something like:

据我所知，用原始SQL对数据表中的序列化列进行整体更新是不容易的。我能想到的最好的办法是:

Car.find_each do |car|
  mpg = car.car_details.delete("fuel_consumption")
  car.car_details["mpg"] = mpg if mpg
  car.save
end

This is assuming that you are using Active Record and your model is called "Car".

这是假设您正在使用活动记录，并且您的模型被称为“Car”。

#2

Well, a previous answer will generate 2000 requests, but you can use the REPLACE function instead. Both MySQL and PostgreSQL have that, so it will be like:

以前的答案将生成2000个请求，但是您可以使用REPLACE函数。MySQL和PostgreSQL都有这种功能，所以会是:

Car.update_all("car_details = REPLACE(car_details, 'fuel_consumption', 'mpg')")

Take a look at the update_all method for the conditions.

查看条件的update_all方法。

还可以看到PostgreSQL字符串函数和MySQL字符串函数。

#1