how to define reference on migration with an existing column rails?

Question

I want to define the foreign key for a model migration using an existing column,I want to set codproducto as foreign key of a table called invmtoproducto, here is my new model migration:

class CreateDetalleinveacs < ActiveRecord::Migration[5.1]
  def change
    create_table :detalleinveacs do |t|
      t.integer :correlativo
      t.integer :cantidad
      t.decimal :valor, precision: 20, scale: 10
      t.decimal :costo, precision: 30, scale: 20
      t.string :nis
      t.datetime :feacceso
      t.integer :codproducto
      t.integer :idinveac
    end
   end
end

Answer 1

You can use

add_foreign_key :detalleinveacs, :invmtoproducto, column: :codproducto

Your migration would then look like this:

class CreateDetalleinveacs < ActiveRecord::Migration[5.1]
  def change
    create_table :detalleinveacs do |t|
      t.integer :correlativo
      t.integer :cantidad
      t.decimal :valor, precision: 20, scale: 10
      t.decimal :costo, precision: 30, scale: 20
      t.string :nis
      t.datetime :feacceso
      t.integer :codproducto
      t.integer :idinveac
    end

    # Add a foreign key constraint 
    # from the 'detalleinveacs' table 
    # to the 'invmtoproducto' table 
    # where the foreign key column 'codproducto' of the 'detalleinveacs' table 
    # references the 'id' column of the 'invmtoproducto' table.
    add_foreign_key :detalleinveacs, :invmtoproducto, column: :codproducto
  end
end

In case the foreign key references a column different than id on the invmtoproducto table, it is possible to override that default:

add_foreign_key :detalleinveacs, 
                :invmtoproducto, 
                column: :codproducto,
                primary_key: :some_column_other_than_id

Please see the documentation for further details