Rails migration to change column type from text to json (Postgresql)

问题

I've been trying unsuccessfully to change a column type in my Postgres database from text to json. Here's what I've tried...

class ChangeNotesTypeInPlaces < ActiveRecord::Migration[5.0]
  def up
    execute 'ALTER TABLE places ALTER COLUMN notes TYPE json USING (notes::json)'
  end

  def down
    execute 'ALTER TABLE places ALTER COLUMN notes TYPE text USING (notes::text)'
  end
end

Also...

class ChangeNotesTypeInPlaces < ActiveRecord::Migration[5.0]
  def up
    change_column :places, :notes, 'json USING CAST(notes AS json)'
  end

  def down
    change_column :places, :notes, 'text USING CAST(notes AS text)'
  end
end

Both of these return the same error...

PG::InvalidTextRepresentation: ERROR:  invalid input syntax for type json

回答1:

Using Rails 5.1.x and PostgreSQL 9.4, here is what worked for me when converting text columns (containing valid json) to jsonb columns :

class ChangeTextColumnsToJson < ActiveRecord::Migration[5.1]
  def change
    change_column :table_name, :column_name, :jsonb, using: 'column_name::text::jsonb'
  end
end

回答2:

I was able to accomplish it using:

def change
  change_column :places, :notes, :json, using: 'notes::JSON'
end

This won't be reversible though; I imagine you can split it out into separate up and down definitions, but I didn't feel the need to.

回答3:

I just solved a similar problem. Trying to adapt it for your question, it would look (mostly?) like this.

class ChangeNotesTypeInPlaces < ActiveRecord::Migration[5.0]
  def up
    change_column :places, :notes, :jsonb, using: 'CAST(value AS JSON)'
  end

  def down
    change_column :places, :notes, :text
  end
end

来源：https://stackoverflow.com/questions/40325426/rails-migration-to-change-column-type-from-text-to-json-postgresql

标签

ruby-on-rails

postgresql

rails-migrations