Rails Adding an index after adding column

Question

Suppose I created a table table in a Rails app  Some time later  I add a column running   rails generate migration AddUser idColumnToTable user id string     Then I realize I need to add user id as an index  I know about the add index method  but where should this method be called  Am I supposed to run a migration  if yes  which one     then adding by hand this method

User · Answer

You can use this  just think Job is the name of the model to which you are adding  index cader id   class AddCaderIdToJob  lt  ActiveRecord  Migration 5 2    def change     change table  jobs do  t        t integer  cader id       t index  cader id     end   end end

User · Answer

If you need to create a user id then it would be a reasonable assumption that you are referencing a user table  In which case the migration shall be   rails generate migration AddUserRefToProducts user references   This command will generate the following migration   class AddUserRefToProducts  lt  ActiveRecord  Migration   def change     add reference  user   product  index  true   end end   After running rake db migrate both a user id column and an index will be added to the products table   In case you just need to add an index to an existing column  e g  name of a user table  the following technique may be helpful   rails generate migration AddIndexToUsers name string index will generate the following migration   class AddIndexToUsers  lt  ActiveRecord  Migration   def change     add column  users   name   string     add index  users   name   end end   Delete add column line and run the migration   In the case described you could have issued rails generate migration AddIndexIdToTable index id integer index command and then delete add column line from the generated migration  But I d rather recommended to undo the initial migration and add reference instead   rails generate migration RemoveUserIdFromProducts user id integer rails generate migration AddUserRefToProducts user references

User · Answer

You can run another migration  just for the index   class AddIndexToTable  lt  ActiveRecord  Migration   def change     add index  table   user id   end end

User · Answer

For references you can call  rails generate migration AddUserIdColumnToTable user references   If in the future you need to add a general index you can launch this  rails g migration AddOrdinationNumberToTable ordination number integer index   Generate code   class AddOrdinationNumberToTable  lt  ActiveRecord  Migration   def change    add column  tables   ordination number   integer    add index  tables   ordination number  unique  true   end end

User · Answer

Add in the generated migration after creating the column the following  example   add index  photographers   email   unique   gt  true

User · Answer

For those who are using postgresql db and facing error StandardError  An error has occurred  this and all later migrations canceled       Dangerous operation detected  strong migrations      Adding an index non-concurrently blocks writes  please refer this article example  class AddAncestryToWasteCodes  lt  ActiveRecord  Migration 6 0    disable ddl transaction     def change     add column  waste codes   ancestry   string     add index  waste codes   ancestry  algorithm   concurrently   end end

[ruby-on-rails] Rails: Adding an index after adding column

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