Relation already exists during rake migration - rake

Question

I have installed a blog engine to refinerycms which is working perfectly.
Now I have generated a migration with some table fields changes (of course not refinerycms or blog tables), but I'm getting an error:
== CreateBlogStructure: migrating ============================================
-- create_table("refinery_blog_posts", {:id=>true})
NOTICE: CREATE TABLE will create implicit sequence "refinery_blog_posts_id_seq1" for serial column "refinery_blog_posts.id"
rake aborted!
An error has occurred, this and all later migrations canceled:
PG::Error: ERROR: relation "refinery_blog_posts" already exists
: CREATE TABLE "refinery_blog_posts" ("id" serial primary key, "title" character varying(255), "body" text, "draft" boolean, "published_at" timestamp, "created_at" timestamp NOT NULL, "updated_at" timestamp NOT NULL)
Tasks: TOP => db:migrate
(See full trace by running task with --trace)

Answer 1

Check your db/schema.rb
You most likely have the same table being created there in addition to a migration in db/migrate/[timestamp]your_migration
You can delete the db/migrate/[timestamp]your_migration if it is a duplicate of the one found in the schema and it should work.

Answer 2

PG::Error: ERROR: relation “refinery_blog_posts” already exists
Pg is a Rails gem, the piece of code that allows communication between Rails and PostgreSQL. It relates your migrations to SQL tables, thus a relation error. So, what the error is saying is:
I'm trying to create table X, based on migration X, but table X
already exists in the database.
Possible solutions:
Create migrations that drop those, probably old, tables.
Change the migration's name.
Login to PostgreSQL and drop the table. Something like:
$ psql -U username databasename
then
database_name=# drop table table-name;
The exact commands might be a little different though.

Answer 3

Adding as this is an obvious but easy to overlook cause of this error (and this is the first post search engines bring up).
If you accidentally defined the same relationship twice in the same migration this is the error that shows up.
def change
create_table :books do |t|
t.belongs_to :author
t.belongs_to :author # Duplicated column definition
end
end
Seems obvious but easy to overlook. To fix just remove the duplicated reference.