ruby on rails - Is there a way to get the create table statement for a migration -

i'm wondering if there's way create table statement migration. instead of run rake db:migrate, if can write invoke migration , instead of running or down, able run instead of getting table created, create table statement instead.

something createfootable.up , able specific if want create table statement sqlite or mysql, etc. possible?

these 2 separate questions:

1. can generate query string (or set of query strings) migration?
2. can select adapter use when running migrations (or generating queries them)?

the short answer both of these "yes, can".

class createfoostable < activerecord::migration   def     create_table :foo |t|       t.int :bar       t.string :baz     end   end end 

to answer second question first, can switch adapter changing activerecord configuration used establish connection:

mysql_config = {   adapter:  "mysql",   host:     "localhost",   username: "myuser",   password: "mypass",   database: "somedatabase" } sqlite_config = {   adapter:  "sqlite",   database: "path/to/dbfile"       }  require "db/migrate/20130711000000_create_foos_table.rb" activerecord::base.establish_connection(mysql_config) createfoostable.up      # run against mysql activerecord::base.establish_connection(sqlite_config) createfoostable.up      # run against sqlite 

now first question, how can generate sql instead of executing it?

the simplest way override execute method output whatever passed in:

# replace 'sqliteadapter' abstractmysqladapter same mysql activerecord::connectionadapters::sqliteadapter.class_eval     def execute(sql, name=nil)     puts sql   end end 

running createfoostable.up should output sql console. if want capture sql strings variable, replace puts sql whatever logic suits needs.

note while overriding execute work create_table, won't job modifying existing tables. because execute needed determine existing schema before generating modification sql. in case, you're better off aliasing , checking if query starts create, alter, or drop before proceeding.