Notes posted by dani

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December 6, 2013
0 thanks

Update the uniqueness field when it value dependent on another existent field without uniqueness restriction.

I’m using sub-transaction to update existent records on DB. I use this approach to update the uniqueness field when it value dependent on another existent field without uniqueness restriction.

Migration for uniqueness with existent dependent data in DB

class AddUniquenessBarToFoo < ActiveRecord::Migration
  class Foo < ActiveRecord::Base
  end

  def change

    add_column :foos, :bar, :string
    execute "ALTER TABLE foos ADD CONSTRAINT uk_foods_bar UNIQUE (bar)"    

    Foo.reset_column_information
    Foo.all.each do |f|
      begin
        #try get unique value in a new sub-transaction
        Foo.transaction(requires_new: true) do
          f.update_attributes!(:bar => "some ops. with another non-unique existent field to set this")
        end
      rescue ActiveRecord::StatementInvalid
         #We can't reuse a crashed transaction. New one.
         Foo.transaction(requires_new: true) do
          #Alternative unique value, if another error exist it's another
          #migration problem and then raise new error.
          f.update_attributes!(:bar => "some operation to set this-#{f.id}")
        end
      end
    end   
    change_column :foos, :bar, :string, :null => false

  end
end

Be aware about performance that is transaction per record for big DB.

December 6, 2013
0 thanks

Migration for uniqueness with existent data in DB

I’m using sub-transaction to update existent records on DB. I use this approach to update the uniqueness field when it value dependent on another existent field without uniqueness restriction.

Migration for uniqueness with existent dependent data in DB

class AddUniquenessBarToFoo < ActiveRecord::Migration
  class Foo < ActiveRecord::Base
  end

  def change

    add_column :foos, :bar, :string
    execute "ALTER TABLE foos ADD CONSTRAINT uk_foods_bar UNIQUE (bar)"    

    Foo.reset_column_information
    Foo.all.each do |f|
      begin
        #try get unique value in a new sub-transaction
        Foo.transaction(requires_new: true) do
          f.update_attributes!(:bar => "some ops. with another non-unique existent field to set this")
        end
      rescue ActiveRecord::StatementInvalid
         #We can't reuse a crashed transaction. New one.
         Foo.transaction(requires_new: true) do
          #Alternative unique value, if another error exist it's another
          #migration problem and then raise new error.
          f.update_attributes!(:bar => "some operation to set this-#{f.id}")
        end
      end
    end   
    change_column :foos, :bar, :string, :null => false

  end
end

Be aware about performance that is transaction per record for big DB.