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

Rails
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

– create_table(:sessions)-
‘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.

Sent from my iPhone

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.