Migration

<!---->1、<!---->Generate migrations

<!---->l         <!---->You can use the “ruby script/generate model model-name” command to generate model and the corresponding migration file.

<!---->l         <!---->You can also generate a migration on its own command:ruby script/generate migration migration-name

2、Running Migrations

       rake db:migrate [VERSION=23]

3、API of ActiveRecord::Migration class

<!---->l         <!---->Column Types

The common options of column:

:null=>true or false(If false,the underlying column has a not null constraint added)

:limit=>size(Requests a maximum column length (:string, :text, :binary or :integer columns only))

:default=>value

<!---->l         <!---->add_column

# Adds a new column to the named table.

# See TableDefinition#column for details of the options you can use.

def add_column(table_name, column_name, type, options = {})

       #.....

end

example:

add_column :orders,:name,:string,:limit=>100,:null=>false

add_column :orders, :age, :integer

add_column :orders, :ship_class, :string, :limit => 15, :default => 'priority'

add_column :orders, :price, :decimal, :precision => 8, :scale => 2

add_column :meter, :reading, :decimal, :precision => 24, :scale => 0

<!---->l         <!---->remove_column

def remove_column(table_name, column_name)

       #....

end

example:

remove_column :products,:price

<!---->l         <!---->rename_column

def rename_column(table, column, new_column_name)

     execute "EXEC sp_rename '#{table}.#{column}', '#{new_column_name}'"

end

example:

rename_column :orders, :e_mail, :customer_email

<!---->l         <!---->change_column

Changes the column’s definition according to the new options.

<!---->l         <!---->create_table

options for create_table

:force=>false or true(If you specify true,the migration will drop an existing table of the same name before creating the new one)

:temporary=>true or false(if youo specify true,the migration will create a temporary table)

:options=>”XXX”

options=>”auto_increment=10000”

example:

create_table :tickets,:options=>”auto_increment=10000” do |t|

       t.column :column_name,:column_type

       …….

end

<!---->l         <!---->drop_table

<!---->l         <!---->rename_table

rename_table(name, new_name)

<!---->l         <!---->add_index:define an index

add_index(table_name, column_name, options = {})

<!---->l         <!---->remove_index

<!---->l         <!---->primary_key

example:

create_table :tickets, :primary_key => :number do |t|

t.column :created_at, :timestamp

t.column :description, :text

end

 

Tables with no primary key

create_table :authors_books, :id => false do |t|

t.column :author_id, :integer, :null => false

t.column :book_id, :integer, :null => false

end

4、Using Native SQL

       You can use “execute” method to execute native sql.For example:

execute “alter table line_items add constraint fk_line_item_products foreign key (product_id) references products(id)”

In this example you use ‘alter’ command to add a foreign key for line_items table.