How to *reversibly* remove a column within `change_table` in a Rails migration?-CodePudding

I know I can do this in a change migration and have it be reversible:

  add_column :widgets, :color, :string
  remove_column :widgets, :flavor, :string

But strangely, change_table->remove does not work like this. Instead of params (name, type), it takes a list of column names. (If you attempt to append a type parameter, it gets interpreted as a column name.)

  change_table(:widgets) do |t|
    t.column :color, :string
    t.remove :flavor, :string    # <-- nope! It tries to remove a column named "string"
  end

When you try that, you get this error:

  remove_columns is only reversible if given a type.

Is there another call I am be overlooking? It seems weird that change_table could be missing such a fundamental use case, but I don't see any calls in the docs that can do it.

CodePudding user response：

While experimenting, I tried this and it works:

  change_table(:widgets) do |t|
    t.column :color, :string
    t.remove :flavor, type: :string
                     #^^^^^
  end

So I guess that's the answer.

CodePudding user response：

ActiveRecord::ConnectionAdapters::Table is generally just a thin wrapper around ActiveRecord::ConnectionAdapters::SchemaStatements - in this case remove_columns which takes a list of columns and an options hash.

type and other column options can be passed to make migration reversible.
remove_columns(:suppliers, :qualification, :experience, type: :string, null: false)

remove really just provides the first argument - which is the table.