Add a default value to a column through a migration

Question

How do I add a default value to a column that already exists through a migration    All the documentation I can find shows you how to do it if the column doesn t already exist but in this case it does

User · Answer

change column default  employees   foreign  false

User · Answer

Here s how you should do it   change column  users   admin   boolean   default   gt  false   But some databases  like PostgreSQL  will not update the field for rows previously created  so make sure you update the field manaully on the migration too

User · Answer

This is what you can do   class Profile  lt  ActiveRecord  Base   before save  set default val    def set default val     self send updates    val  unless self send updates   end end   EDIT     but apparently this is a Rookie mistake

User · Answer

Execute   rails generate migration add column to table column boolean   It will generate this migration   class AddColumnToTable  lt  ActiveRecord  Migration   def change     add column  table   column   boolean   end end   Set the default value adding  default    1     add column  table   column   boolean   default    1   Run      rake db migrate

User · Answer

Using def change means you should write migrations that are reversible  And change column is not reversible  You can go up but you cannot go down  since change column is irreversible   Instead  though it may be a couple extra lines  you should use def up and def down  So if you have a column with no default value  then you should do this to add a default value   def up   change column  users   admin   boolean  default  false end  def down   change column  users   admin   boolean  default  nil end   Or if you want to change the default value for an existing column   def up   change column  users   admin   boolean  default  false end  def down   change column  users   admin   boolean  default  true end

User · Answer

Rails 4 X      As of Rails 4 you can t generate a migration to add a column to a table with a default value  The following steps add a new column to an existing table with default value true or false   1  Run the migration from command line to add the new column    rails generate migration add columnname to tablename columnname boolean   The above command will add a new column in your table   2  Set the new column value to TRUE FALSE by editing the new migration file created   class AddColumnnameToTablename  lt  ActiveRecord  Migration   def change     add column  table name   column name   boolean  default  false   end end     3  To make the changes into your application database table  run the following command in terminal      rake db migrate

User · Answer

For Rails 4   use change column default  def change   change column default  table   column  value end

[ruby-on-rails] Add a default value to a column through a migration

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