newb here trying to understand an issue with rolling back migrations then re-running them

rubyonrails-talk
1

I’m sure this is total newb (since I am pretty newb) but I’m curious what the issue is here. I attempt to role back all my migrations which I’m doing with

rake db:migrate VERSION=0 (in /Users/rick/projects/rails/sillymeters)

== CreateSessions: never migrated, skipping ==================================

== CreateUsers: reverting ==================================================== – drop_table(:users) → 0.0011s == CreateUsers: reverted (0.0012s) ===========================================

== CreateMeters: reverting =================================================== – drop_table(:meters) → 0.0008s == CreateMeters: reverted (0.0009s) ==========================================

etc…

Note the first one says “CreateSessions: never migrated, skipping”

When I then go to run the migrations, most go through fine, but then I get the following error when it tries to run the CreateSessions migration:

~/projects/rails/sillymeters(master) $ rake db:migrate (in /Users/rick/projects/rails/sillymeters) == CreateSessions: migrating ================================================= – create_table(:sessions)-

rake aborted! An error has occurred, this and all later migrations canceled:

SQLite3::SQLException: table “sessions” already exists: CREATE TABLE “sessions” (“id” INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, “session_id” varchar(255) NOT NULL, “data” text, “created_at” datetime, “updated_at” datetime)

I’m assuming that each application has its own instance of SQLLite so I’m curious how this error is occurring or what I need to do to fix it. I ‘think’ I might be getting this because it’s possible I did at one point have a similar migration that created the Session table, but then I deleted that migration and created it as a new one with a new name. The table name was the same though “sessions” so I don’t get what is going on.

The migration in question looks like:

class CreateSessions < ActiveRecord::Migration def self.up create_table :sessions do |t| t.string :session_id, :null => false t.text :data

  t.timestamps
end

add_index :sessions, :session_id
add_index :sessions, :updated_at

end

def self.down drop_table :sessions end end

2

Note the first one says "CreateSessions: never migrated, skipping"

When I then go to run the migrations, most go through fine, but then I get the following error when it tries to run the CreateSessions migration:

~/projects/rails/sillymeters(master) $ rake db:migrate (in /Users/rick/projects/rails/sillymeters) == CreateSessions: migrating

-- create_table(:sessions)- rake aborted! An error has occurred, this and all later migrations canceled:

SQLite3::SQLException: table "sessions" already exists: CREATE TABLE "sessions" ("id" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, "session_id" varchar(255) NOT NULL, "data" text, "created_at" datetime, "updated_at" datetime)

I'm assuming that each application has its own instance of SQLLite so I'm curious how this error is occurring or what I need to do to fix it. I 'think' I might be getting this because it's possible I did at one point have a similar migration that created the Session table, but then I deleted that migration and created it as a new one with a new name. The table name was the same though "sessions" so I don't get what is going on.

Rails tracks migrations that have be run with the schema_migrations (which contains the numerical identifier for each migration). If you created a new migration then that migration won't be recorded as having being run (which is why migrate VERSION=0 doesn't do anything) but the table is of course still there, so trying to create it again raises an error

Fred

3

You can run the following command:

script/dbconsole

And then manually drop the sessions table (drop sessions). Then try full rollbacks and migrations again.

4

Check to see if you have duplicate code in any of your migrations to create this table:

SQLite3::SQLException: table "sessions" already exists: CREATE TABLE "sessions" ("id" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, "session_id" varchar(255) NOT NULL, "data" text, "created_at" datetime, "updated_at" datetime)

This can easily happen if you have code to create all your tables in the main CreateDatabase migration file, then run script/generate to generate scaffolding or a model for an existing table. The generator script will create a new migration with table creation code, causing rake to choke the next time you do a migration.