Migration Duplication Error

Question

My Error

== 20150727183532 ActsAsTaggableOnMigration: migrating ======================== -- create_table(:tags) rake aborted! StandardError: An error has occurred, this and all later migrations canceled:

PG::DuplicateTable: ERROR: relation "tags" already exists : CREATE TABLE "tags" ("id" serial primary key, "name" character varying)

Second Migration in Database:

    create_table :tags do |t|
        t.string            :name
        t.integer           :taggings_count, default: 0
    end
    add_index :tags, :name, unique: true


    create_table :taggings do |t|
        t.references        :tag
        t.references        :taggable,      polymorphic: true
        t.references        :tagger,        polymorphic: true
        t.string                :context,       limit: 128
        t.datetime          :created_at
    end
    add_index :taggings, [ :tag_id, :taggable_id, :taggable_type, :context, :tagger_id, :tagger_type ],
        unique: true, name: 'taggings_idx'

end

This is a later migration where the problem appears to be coming from?

def self.up

create_table :tags do |t|
  t.string :name
end

create_table :taggings do |t|
  t.references :tag

  # You should make sure that the column created is
  # long enough to store the required class names.
  t.references :taggable, polymorphic: true
  t.references :tagger, polymorphic: true

  Limit is created to prevent MySQL error on index
  # length for MyISAM table type: http://bit.ly/vgW2Ql
  t.string :context, limit: 128

  t.datetime :created_at
end

add_index :taggings, :tag_id
add_index :taggings, [:taggable_id, :taggable_type, :context]

end

def self.down drop_table :taggings drop_table :tags end

I am trying to understand what the person that made this migration was intending to do.

user589888 user589888 · Accepted Answer · 2015-07-27T20:16:11

This can't be intentional, because it can't work. As you've seen, you can't create a table twice. You should delete one of the migrations, possibly merging from the one you delete into the other one.

The only differences are the taggings_count field and the indexes. There isn't enough to go on here to say whether you need taggings_count or which is the better index. If I had to guess, I'd say the index on the first was trying to create a covering index, for what that's worth.

Migration Duplication Error

3 Answers