Error map
ActiveRecord::ConnectionNotEstablished Rails: ActiveRecord::ConnectionNotEstablished: No connection pool for 'ActiveRecord::Base' found
Ruby / Rails · layer 4, Application & API
Centre: this error. First ring: errors it is linked with (12). Outer ring: what those are linked with. Colours show the layer of a request each error belongs to. Click any dot to re-centre the map on it; hover to follow its connections. The centre dot opens the error page.
Directly related (12)
Rails: ActionController::InvalidAuthenticityToken (Can't verify CSRF token authenticity)
A non-GET request arrived without a valid CSRF token for the session.
Redis: Error: read ECONNRESET / redis.exceptions.ConnectionError: Connection reset by peer after idle time
A middlebox or Redis closed an idle connection, and the pooled client reused it.
Rails: ActiveRecord::RecordNotFound: Couldn't find User with 'id'=42
`find`/`find_by!` didn't find a row, so Rails raises (and renders a 404 in production).
Rails: ActiveRecord::StatementInvalid: PG::UndefinedTable: ERROR: relation "users" does not exist
Rails queried a table that isn't in the connected PostgreSQL database.
Rails: ActiveRecord::StatementInvalid: PG::DuplicateColumn: ERROR: column "status" of relation "orders" already exists
A migration tried to add a column/table/index that already exists.
Rails: ActionController::UrlGenerationError: No route matches {:action=>"show", :controller=>"users", :id=>nil}, missing required keys: [:id]
A URL helper (`user_path(@user)`) was called without a value Rails needs (usually `nil` object).
Rails: ActionView::Template::Error (undefined method `name' for nil:NilClass): app/views/users/show.html.erb:3
A view called a method on `nil` (or an undefined helper), so rendering failed — the error is wrapped in `ActionView::Template::Er…
Rails: ActionController::RoutingError (No route matches [GET] "/users/new")
The request path/method doesn't match any route in `config/routes.rb` (a 404 in production).
Rails: ActiveRecord::RecordNotUnique: PG::UniqueViolation: ERROR: duplicate key value violates unique constraint "index_users_on_email"
A unique index rejected an insert/update because the value already exists.
Rails: ActiveRecord::IrreversibleMigration — This migration uses remove_column without a type; db:rollback can't reverse it
`rails db:rollback` can't undo the migration because it contains an operation Rails can't invert.
Rails: ActionView::MissingTemplate (Missing template users/show, application/show with {:locale=>[:en], :formats=>[:html], :handlers=>[:erb, :builder, :raw, :ruby, :jbuilder]})
The action tried to render a view that doesn't exist for the requested format/handler.
Browser: Access to fetch at 'http://localhost:3000/api/items' from origin 'http://localhost:5173' has been blocked by CORS policy — Rails
The browser blocks calls from your front end to the Rails API because CORS headers are missing.
Two steps away (27)
Laravel: 419 Page Expired (CSRF token mismatch)
Laravel rejected a POST because the CSRF token was missing, expired or didn’t match the session.
Forbidden (403) CSRF verification failed. Request aborted.
Django rejected a POST because the CSRF token was missing, wrong, or the request origin isn’t trusted.
OAuth callback error: state mismatch / Unable to verify authorization request state / State cookie was missing
The state value returned to the callback doesn’t match what the app stored before redirecting — the CSRF protection for OAuth fai…
Laravel: SQLSTATE[HY000] [2002] Connection refused (SQL: select * from sessions) / php_network_getaddresses: getaddrinfo failed
Laravel can't open a network connection to the database host and port from `.env`.
Laravel: Predis\Connection\ConnectionException: Connection refused [tcp://127.0.0.1:6379] / RedisException: Connection refused
Laravel can't connect to Redis, which it uses for cache, sessions or queues.
Redis: Error: connect ECONNREFUSED 127.0.0.1:6379 / Could not connect to Redis at 127.0.0.1:6379: Connection refused
Nothing is listening on the Redis host/port your client uses.
Ruby: NoMethodError: undefined method `x' for nil (nil:NilClass)
You called a method on nil — the object you expected (a record, hash value, param) wasn’t there.
Rails: ActiveRecord::RecordInvalid: Validation failed: Email can't be blank, Name is too short
`save!`/`create!`/`update!` raised because validations failed.
Rails: PG::ConnectionBad: could not connect to server: Connection refused. Is the server running on host "localhost" (127.0.0.1) and accepting TCP/IP connections on port 5432?
Rails can't reach PostgreSQL — the server is down, wrong host/port/socket, or credentials/pg_hba block it.
Rails: ActiveRecord::PendingMigrationError — Migrations are pending. To resolve this issue, run: bin/rails db:migrate
The database schema is behind the migration files in the app.
Rails: ActiveRecord::StatementInvalid: Mysql2::Error: Unknown column 'users.nickname' in 'field list'
The query references a column that doesn't exist in the table (missing migration, typo or stale schema cache).
Rails: ActiveRecord::Deadlocked: PG::TRDeadlockDetected: ERROR: deadlock detected
Two transactions locked rows in opposite orders, so PostgreSQL aborted one.
MySQL ERROR 1146 (42S02): Table 'db.table' doesn't exist
The query references a table that MySQL can’t find in that database.
PostgreSQL: ERROR: relation "x" does not exist
The table/view isn’t found — missing migration, wrong schema, or a case-sensitive quoted name.
MySQL ERROR 1022 (23000): Can't write; duplicate key in table
An ALTER/CREATE produced a duplicate key or constraint name — often a foreign key name that already exists in the database.
connect: Network is unreachable (ENETUNREACH)
The host has no route to the destination network — no default gateway, interface down, or trying IPv6 without IPv6 connectivity.
Rails: ActiveRecord::AssociationTypeMismatch: User(#1234) expected, got "42" which is an instance of String(#5678)
You assigned the wrong kind of object (or an id string) to an association.
MySQL ERROR 1062 (23000): Duplicate entry for key
An INSERT/UPDATE would create a duplicate value in a PRIMARY or UNIQUE key.
MySQL ERROR 1452: Cannot add or update a child row: a foreign key constraint fails
You inserted/updated a row whose foreign key value doesn’t exist in the referenced parent table.
PostgreSQL: ERROR: duplicate key value violates unique constraint
An INSERT/UPDATE would create a duplicate in a UNIQUE or PRIMARY KEY column — or the id sequence is behind the existing data.
MySQL ERROR 1051 (42S02): Unknown table 'x'
DROP TABLE targeted a table that doesn’t exist.
MySQL ERROR 1060 (42S21): Duplicate column name 'x'
A CREATE/ALTER adds a column that already exists, or a SELECT in a view/derived table produces two columns with the same name.
MySQL ERROR 1061 (42000): Duplicate key name 'x'
CREATE INDEX/ADD INDEX used an index name that already exists on the table.
Rails: ActionController::UnknownFormat — UsersController#show is missing a template for this request format and variant
The controller has no template or `respond_to` handler for the requested format (HTML/JSON/etc.).
Rails: AbstractController::DoubleRenderError (Render and/or redirect were called multiple times in this action. Please note that you may only call render OR redirect, and at most once per action)
An action called `render`/`redirect_to` more than once.
Browser: Access to XMLHttpRequest at 'https://api.example.com' from origin 'http://localhost:3000' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header — Laravel
The browser blocked a cross-origin call to your Laravel API because the response lacks the right CORS headers.
Browser: Access to fetch at 'https://api.example.com/api/data' from origin 'https://app.example.com' has been blocked by CORS policy (Next.js route handler)
A cross-origin request to your Next.js API route is blocked because the response lacks CORS headers.
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