why PG::UniqueViolation: ERROR: duplicate key value violates unique constraint?

Question

I have a model Post and each time a post is created I want a new instance of Moderation to be created at the same time.

So in post.rb I use the callback after_save :create_moderation Then write a private method :

 ...  include Reportable  after_save :create_moderation   private  def create_moderation     self.create_moderation!(blog: Blog.first)  end 

But when a proposal is created I get this error :

PG::UniqueViolation: ERROR: duplicate key value violates unique constraint "moderations_reportable" DETAIL: Key (reportable_type, reportable_id)=(Post, 25) already exists. : INSERT INTO "moderations" ("blog_id", "reportable_type", "reportable_id", "created_at", "updated_at", "blog_type") VALUES ($1, $2, $3, $4, $5, $6) RETURNING "id"

In reportable.rb I have :

  has_one :moderation, as: :reportable, foreign_key: "reportable_id", foreign_type: "reportable_type", class_name: "Moderation" 

Then few other methods for reportable object.

Note that this issue doesn't happen when I run the create method in console.

EDIT

  create_table "moderations", id: :serial, force: :cascade do |t|     t.string "reportable_type", null: false     t.string "reportable_id", null: false     t.integer "blog_id", null: false     t.datetime "created_at", null: false     t.datetime "updated_at", null: false     t.string "blog_type", null: false     t.string "upstream_moderation", default: "unmoderate"     t.index ["blog_id", "blog_type"], name: "moderations_blog"     t.index ["reportable_type", "reportable_id"], name: "moderations_reportable", unique: true   end    create_table "posts", id: :serial, force: :cascade do |t|     t.text "title", null: false     t.text "body", null: false     t.integer "feature_id", null: false     t.integer "author_id"     t.integer "scope_id"     t.datetime "created_at", null: false     t.datetime "updated_at", null: false     t.integer "post_votes_count", default: 0, null: false     t.index ["body"], name: "post_body_search"     t.index ["created_at"], name: "index_posts_on_created_at"     t.index ["author_id"], name: "index_posts_on_author_id"     t.index ["feature_id"], name: "index_posts_on_feature_id"     t.index ["proposal_votes_count"], name: "index_posts_on_post_votes_count"     t.index ["title"], name: "post_title_search"   end 

Answer 1

To fix the issue, we have to tell ActiveRecord to look at the sequence of the table:

ActiveRecord::Base.connection.reset_pk_sequence!('table_name') 

Now ActiveRecord should have the correct sequence value, and should be able to assign new id's properly.

To resolve error

PG::UniqueViolation: ERROR: duplicate key value violates unique constraint "moderations_reportable" DETAIL: Key (reportable_type, reportable_id)=(Post, 25) already exists. : INSERT INTO "moderations" ("blog_id", "reportable_type", "reportable_id", "created_at", "updated_at", "blog_type") VALUES ($1, $2, $3, $4, $5, $6) RETURNING "id"

As error occurred on 'moderations' table.

Run the following from rails console fix

ActiveRecord::Base.connection.reset_pk_sequence!('moderations') 

Thank you