Rails migration for change column

Question

We have script generate migration add fieldname to tablename fieldname datatype syntax for adding new columns to a model   On the same line  do we have a script generate for changing the datatype of a column  Or should I write SQL directly into my vanilla migration   I want to change a column from datetime to date

User · Answer

Just generate migration   rails g migration change column to new from table name   Update migration like this   class ClassName  lt  ActiveRecord  Migration   change table  table name do  table      table change  column name   data type   end end   and finally  rake db migrate

User · Answer

To complete answers in case of editing default value    In your rails console    rails g migration MigrationName   In the migration      def change     change column  tables   field name   field type  default  value   end   Will look like      def change     change column  members   approved   boolean  default  true   end

User · Answer

I m not aware if you can create a migration from the command line to do all this  but you can create a new migration  then edit the migration to perform this taks   If tablename is the name of your table  fieldname is the name of your field and you want to change from a datetime to date  you can write a migration to do this   You can create a new migration with   rails g migration change data type for fieldname   Then edit the migration to use change table   class ChangeDataTypeForFieldname  lt  ActiveRecord  Migration   def self up     change table  tablename do  t        t change  fieldname   date     end   end   def self down     change table  tablename do  t        t change  fieldname   datetime     end   end end   Then run the migration   rake db migrate

User · Answer

You can also use a block if you have multiple columns to change within a table   Example   change table  table name do  t    t change  column name   column type   options  end   See the API documentation on the Table class for more details

User · Answer

I think this should work   change column  table name   column name   date

User · Answer

This is all assuming that the datatype of the column has an implicit conversion for any existing data  I ve run into several situations where the existing data  let s say a String can be implicitly converted into the new datatype  let s say Date    In this situation  it s helpful to know you can create migrations with data conversions  Personally  I like putting these in my model file  and then removing them after all database schemas have been migrated and are stable    app models table rb         def string to date     update new date field  date field to date    end    def date to string     update old date field  date field to s    end             def up           Add column to store converted data         add column  table name   new date field   date           Update the all resources         Table all each  amp  string to date            Remove old column         remove column  table name   date field           Rename new column         rename column  table name   new date field   date field     end        Reversed steps does allow for migration rollback     def down         add column  table name   old date field   string         Table all each  amp  date to string          remove column  table name   date field         rename column  table name   old date field   date field     end

User · Answer

Another way to change data type using migration  step1    You need to remove the faulted data type field name using migration  ex   rails g migration RemoveFieldNameFromTableName field name data type   Here don t forget to specify data type for your field  Step 2    Now you can add field with correct data type  ex   rails g migration AddFieldNameToTableName field name data type   That s it  now your table will added with correct data type field  Happy ruby coding

User · Answer

With Rails 5  From Rails Guides      If you wish for a migration to do something that Active Record doesn   t know how to reverse  you can use reversible    class ChangeTablenameFieldname  lt  ActiveRecord  Migration 5 1    def change     reversible do  dir        change table  tablename do  t          dir up     t change  fieldname   date           dir down   t change  fieldname   datetime         end     end   end end

User · Answer

As I found by the previous answers  three steps are needed to change the type of a column   Step 1   Generate a new migration file using this code   rails g migration sample name change column type   Step 2    Go to  db migrate folder and edit the migration file you made  There are two different solutions    def change     change column  table name   column name   new type  end    2       def up         change column  table name   column name   new type     end      def down         change column  table name   column name   old type     end   Step 3   Don t forget to do this command   rake db migrate   I have tested this solution for Rails 4 and it works well

[ruby-on-rails] Rails migration for change column

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