How do I make a column unique and index it in a Ruby on Rails migration

Question

I would like to make a column unique in Ruby on Rails migration script  What is the best way to do it  Also is there a way to index a column in a table   I would like to enforce unique columns in a database as opposed to just using  validate uniqueness of

User · Answer

I m using Rails 5 and the above answers work great  here s another way that also worked for me  the table name is  people and the column name is  email address   class AddIndexToEmailAddress  lt  ActiveRecord  Migration 5 0    def change     change table  people do  t        t index  email address  unique  true     end   end end

User · Answer

You might want to add name for the unique key as many times the default unique key name by rails can be too long for which the DB can throw the error   To add name for your index just use the name  option  The migration query might look something like this -  add index  table name    column name a   column name b       column name n   unique  true  name   my custom index name   More info - http   apidock com rails ActiveRecord ConnectionAdapters SchemaStatements add index

User · Answer

If you are creating a new table  you can use the inline shortcut     def change     create table  posts do  t        t string  title  null  false  index    unique  true         t timestamps     end   end

User · Answer

add index  table name   column name  unique  true   To index multiple columns together  you pass an array of column names instead of a single column name

User · Answer

rails generate migration add index to table name column name uniq   or     rails generate migration add column name to table name column name string uniq index   generates  class AddIndexToModerators  lt  ActiveRecord  Migration   def change     add column  moderators   username   string     add index  moderators   username  unique  true   end end   If you re adding an index to an existing column  remove or comment the add column line  or put in a check  add column  moderators   username   string unless column exists   moderators   username

User · Answer

The short answer for old versions of Rails  see other answers for Rails 4     add index  table name   column name  unique  true   To index multiple columns together  you pass an array of column names instead of a single column name   add index  table name    column name a   column name b   unique  true   If you get  index name    is too long   you can add name   whatever  to the add index method to make the name shorter    For fine-grained control  there s a  execute  method that executes straight SQL   That s it   If you are doing this as a replacement for regular old model validations  check to see how it works  The error reporting to the user will likely not be as nice without model-level validations  You can always do both

User · Answer

If you have missed to add unique to DB column  just add this validation in model to check if the field is unique   class Person  lt  ActiveRecord  Base   validates uniqueness of  user name end   refer here Above is for testing purpose only  please add index by changing DB column as suggested by  Nate  please refer this with index for more information

User · Answer

Since this hasn t been mentioned yet but answers the question I had when I found this page  you can also specify that an index should be unique when adding it via t references or t belongs to   create table  accounts do  t    t references  user  index    unique  true     or t belongs to      other columns    end    as of at least Rails 4 2 7

[ruby-on-rails] How do I make a column unique and index it in a Ruby on Rails migration?

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