How to drop columns using Rails migration

Question

What s the syntax for dropping a database table column through a Rails migration

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remove column in change method will help you to delete the column from the table   class RemoveColumn  lt  ActiveRecord  Migration   def change     remove column  table name   column name   data type   end end   Go on this link for complete reference   http   guides rubyonrails org active record migrations html

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Give below command it will add in migration file on its own  rails g migration RemoveColumnFromModel   After running above command you can check migration file remove column code must be added there on its own  Then migrate the db  rake db migrate

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Rails 4 has been updated  so the change method can be used in the migration to drop a column and the migration will successfully rollback   Please read the following warning for Rails 3 applications   Rails 3 Warning  Please note that when you use this command   rails generate migration RemoveFieldNameFromTableName field name datatype   The generated migration will look something like this     def up     remove column  table name   field name   end    def down     add column  table name   field name   datatype   end   Make sure to not use the change method when removing columns from a database table  example of what you don t want in the migration file in Rails 3 apps      def change     remove column  table name   field name   end   The change method in Rails 3 is not smart when it comes to remove column  so you will not be able to rollback this migration

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You can try the following   remove column  table name   column name    Official documentation

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Remove Columns For RAILS 5 App  rails g migration Remove lt Anything gt From lt TableName gt   columnName type    Command above generate a migration file inside db migrate directory  Snippet blow is one of remove column from table example generated by Rails generator   class RemoveAgeFromUsers  lt  ActiveRecord  Migration   def up     remove column  users   age   end   def down     add column  users   age   integer   end end   I also made a quick reference guide for Rails which can be found at here

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Simply  You can remove column  remove column  table name   column name   For Example   remove column  posts   comment

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Generate a migration to remove a column such that if it is migrated  rake db migrate   it should drop the column  And it should add column back if this migration is rollbacked  rake db rollback    The syntax   remove column  table name   column name   type     Removes column  also adds column back if migration is rollbacked    Example    remove column  users   last name   string   Note  If you skip the data type  the migration will remove the column successfully but if you rollback the migration it will throw an error

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Clear  amp  Simple Instructions for Rails 5  amp  6  WARNING  You will lose data if you remove a column from your database  To proceed  see below  Warning  the below instructions are for trivial migrations  For complex migrations with e g  millions and millions of rows  you will have to account for the possibility of failures  you will also have to think about how to optimise your migrations so that they run swiftly  and the possibility that users will use your app while the migration process is occurring  If you have multiple databases  or if anything is remotely complicated  then don t blame me if anything goes wrong    1  Create a migration Run the following command in your terminal  rails generate migration remove fieldname from tablename fieldname fieldtype Note  the table name should be in plural form as per rails convention  Example  In my case I want to remove the accepted column  a boolean value  from the quotes table  rails g migration RemoveAcceptedFromQuotes accepted boolean See the documentation re  a convention when adding removing fields to a table   There is a special syntactic shortcut to generate migrations that add fields to a table  rails generate migration add fieldname to tablename fieldname fieldtype  2  Check the migration   db migrate 20190122035000 remove accepted from quotes rb class RemoveAcceptedFromQuotes  lt  ActiveRecord  Migration 5 2      with rails 5 2 you don t need to add a separate  quot up quot  and  quot down quot  method    def change     remove column  quotes   accepted   boolean   end end  3  Run the migration rake db migrate or rails db migrate  they re both the same      And then you re off to the races

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Heres one more from rails console  ActiveRecord  Migration remove column  table name   column name

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In a rails4 app it is possible to use the change method also for removing columns  The third param is the data type and in the optional forth you can give options  It is a bit hidden in the section  Available transformations  on the documentation    class RemoveFieldFromTableName  lt  ActiveRecord  Migration   def change     remove column  table name   field name   data type       end end

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For older versions of Rails   ruby script generate migration RemoveFieldNameFromTableName field name datatype   For Rails 3 and up  rails generate migration RemoveFieldNameFromTableName field name datatype

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Do like this   rails g migration RemoveColumnNameFromTables column name type  I e  rails g migration RemoveTitleFromPosts title string  Anyway  Would be better to consider about downtime as well since the ActiveRecord caches database columns at runtime so if you drop a column  it might cause exceptions until your app reboots   Ref  Strong migration

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Through remove column  table name   column name in a migration file  You can remove a column directly in a rails console by typing  ActiveRecord  Base remove column  table name   column name

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rails g migration RemoveXColumnFromY column name data type   X   column name  Y   table name  EDIT  Changed RemoveXColumnToY to RemoveXColumnFromY as per comments - provides more clarity for what the migration is actually doing

User · Answer

in rails 5 you can use this command in the terminal   rails generate migration remove COLUMNNAME from TABLENAME COLUMNNAME DATATYPE   for example to remove the column access level string  from table users   rails generate migration remove access level from users access level string   and then run   rake db migrate

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first try to create a migration file running the command   rails g migration RemoveAgeFromUsers age string   and then on the root directory of the project run the migration running the command   rails db migrate

User · Answer

There are two good ways to do this   remove column  You can simply use remove column  like so   remove column  users   first name   This is fine if you only need to make a single change to your schema   change table block  You can also do this using a change table block  like so   change table  users do  t    t remove  first name end   I prefer this as I find it more legible  and you can make several changes at once   Here s the full list of supported change table methods   http   apidock com rails ActiveRecord ConnectionAdapters SchemaStatements change table

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remove column  table name   column name   For instance   remove column  users   hobby   would remove the hobby Column from the users table

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To remove the column from table you have to run following migration   rails g migration remove column name from table name column name data type   Then run command   rake db migrate

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For removing column from table in just easy 3 steps as follows    write this command    rails g migration remove column from table name  after running this command in terminal one file created by this name and time stamp  remove column from table name    Then go to this file    inside file you have to write  remove column  table name   column name Finally go to the console and then do  rake db migrate

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