如何将ActiveRecord模型属性从json迁移到jsonb? [英] How do I migrate an ActiveRecord model attribute from json to jsonb?

问题描述

迁移应该是什么样的?我想利用jsonb数组查询技术.

What should the migration look like? I would like to take advantage of the jsonb array querying technique.

推荐答案

我会这样写迁移:

def change
  reversible do |dir|
    dir.up { change_column :models, :attribute, 'jsonb USING CAST(attribute AS jsonb)' }
    dir.down { change_column :models, :attribute, 'json USING CAST(attribute AS json)' }
  end
end

我不知道这在性能上与其他解决方案相比如何，但是我在具有120,000条记录的表上对此进行了测试，每条记录具有4个json列，迁移该表花了我大约一分钟的时间.当然，我想这取决于json结构的复杂程度.

I don't know how this compares performance-wise to other solutions, but I tested this on a table with 120,000 records, each record having four json columns and it took me about a minute to migrate that table. Of course, I guess it depends on how complex the json structure is.

此外，请注意，如果您现有的记录的默认值是{}，则必须添加到上述语句default: {}，因为否则您将拥有jsonb列，但是默认值将保留为'{}'::json.

Also, notice that if your existing records have a default value of {}, you have to add to the above statements default: {}, because otherwise you'll have jsonb columns, but the default value will remain as '{}'::json.

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