Adding Data to a Database Table

1
Adding Data to a Database Table

• Carol Wolf
• Computer Science

2
Adding data to a books table

• Create a books table using
• rails generate scaffold book isbnstring
  authorstring titlestring
• We can add data to the table using the New Book
  link at the bottom of the index page.
• This is slow and for tables with a large number
  of fields very cumbersome.
• Instead a lot of data can be added at once using
  either a migration or modifying seeds.rb in the
  db folder.

3
Using a migration

• Create a migration using
• rails generate migration add_data
• This produces
• class AddData lt ActiveRecordMigration
• def self.up
• end
•  
• def self.down
• end
• end
• Add data to get the following

4

• class AddData lt ActiveRecordMigration
• def self.up
• Book.create(
• isbn gt '4567-8901',
• author gt 'Chekov',
• title gt 'The Cherry Orchard'
• )
• Book.create(
• isbn gt 3412-4598,
• author gt Hemmingway,
• title gt The Sun Also Rises
• )
• end
•  
• def self.down
• Book.delete_all
• end
• end

5
Modifying seeds.rb

• seeds.rb is in the db folder.
• It is generated along with everything else when a
  new rails project is created.
• This file should contain all the record
  creation needed to seed the database with its
  default values.
• The data can then be loaded with the rake
  dbseed (or created alongside the db with
  dbsetup).
• Examples
• cities City.create( name gt 'Chicago' ,
  name gt 'Copenhagen' )
• Mayor.create(name gt 'Daley', city gt
  cities.first)
• You can add data to it using the form indicated.
  
• It is run using rake dbseed. (Note no plural)

6

• This file should contain all the record
  creation needed to seed the database with its
  default values.
• The data can then be loaded with the rake
  dbseed (or created alongside the db with
  dbsetup).
• Examples
• cities City.create( name gt 'Chicago' ,
  name gt 'Copenhagen' )
• Mayor.create(name gt 'Daley', city gt
  cities.first)
•  
• books Book.create(
• isbn gt '4567-8901', author gt 'Chekov',
  title gt 'The Cherry Orchard',
• isbn gt '3412-4598', author gt
  'Hemmingway', title gt 'The Sun Also Rises',
• isbn gt '1357-2468', author gt
  'Steinbeck', title gt 'The Grapes of Wrath'
• )
• Note the curly braces around the hashes and the
  square brackets around all the data.
• This is shorter than the migration and easier to
  do. But they both work.