Error map

CORS blocked in Rails API (rack-cors) Browser: Access to fetch at 'http://localhost:3000/api/items' from origin 'http://localhost:5173' has been blocked by CORS policy — Rails

Ruby / Rails · layer 4, Application & API

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Centre: this error. First ring: errors it is linked with (7). 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.

1 · On your device 4 · Application & API 5 · Data
CORS blocked in Rails API (rack-cors) — Browser: Access to fetch at 'http://localhost:3000/api/items' from origin 'http://localhost:5173' has been blocked by CORS policy — Rails (Ruby / Rails)CORS blocke…CORS blocked (Laravel API) — 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 (Laravel)CORS blocked (Larav…CORS error calling Next.js API route / route handler — 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) (Next.js)CORS error calling …ActiveRecord::IrreversibleMigration — Rails: ActiveRecord::IrreversibleMigration — This migration uses remove_column without a type; db:rollback can't reverse it (Ruby / Rails)ActiveRecord::Irrev…ActiveRecord::ConnectionNotEstablished — Rails: ActiveRecord::ConnectionNotEstablished: No connection pool for 'ActiveRecord::Base' found (Ruby / Rails)ActiveRecord::Conne…PG::ConnectionBad: could not connect to server — 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? (Ruby / Rails)PG::ConnectionBad: …ActiveRecord::Deadlocked: PG::TRDeadlockDetected — Rails: ActiveRecord::Deadlocked: PG::TRDeadlockDetected: ERROR: deadlock detected (Ruby / Rails)ActiveRecord::Deadl…ActiveRecord::AssociationTypeMismatch — Rails: ActiveRecord::AssociationTypeMismatch: User(#1234) expected, got "42" which is an instance of String(#5678) (Ruby / Rails)ActiveRecord::Assoc…Attempt to read property "x" on null — Laravel/PHP 8: ErrorException: Attempt to read property "name" on null (Laravel)Attempt to read pro…429 Too Many Requests (Laravel throttle) — Laravel: Illuminate\Http\Exceptions\ThrottleRequestsException: Too Many Attempts. / 429 Too Many Requests (Laravel)429 Too Many Reques…Sanctum: 401 Unauthenticated — Laravel Sanctum: {"message":"Unauthenticated."} 401 on API / SPA requests (Laravel)Sanctum: 401 Unauth…Hydration error: <div> cannot be a descendant of <p> — Next.js: Warning: validateDOMNesting(...): <div> cannot appear as a descendant of <p> / In HTML, <p> cannot be a descendant of <p>. This will cause a hydration error (Next.js)Hydration error: <d…createContext only works in Client Components — Next.js: You're importing a component that needs createContext. It only works in a Client Component but none of its parents are marked with "use client" (Next.js)createContext only …Route used params.x — params should be awaited — Next.js 15: Error: Route "/blog/[slug]" used `params.slug`. `params` should be awaited before using its properties (Next.js)Route used params.x…1146 — MySQL ERROR 1146 (42S02): Table 'db.table' doesn't exist (MySQL)114642P01 — PostgreSQL: ERROR: relation "x" does not exist (PostgreSQL)42P011022 — MySQL ERROR 1022 (23000): Can't write; duplicate key in table (MySQL)1022ActionController::InvalidAuthenticityToken — Rails: ActionController::InvalidAuthenticityToken (Can't verify CSRF token authenticity) (Ruby / Rails)ActionController::I…Error: connect ECONNREFUSED 127.0.0.1:6379 — Redis: Error: connect ECONNREFUSED 127.0.0.1:6379 / Could not connect to Redis at 127.0.0.1:6379: Connection refused (Redis)Error: connect ECON…Redis TLS: SSL handshake error / protocol mismatch — Redis: Error: write EPROTO ... SSL routines:ssl3_get_record:wrong version number / Connection reset by peer (TLS vs plaintext) (Redis)Redis TLS: SSL hand…ActiveRecord::RecordNotFound: Couldn't find X with 'id'= — Rails: ActiveRecord::RecordNotFound: Couldn't find User with 'id'=42 (Ruby / Rails)ActiveRecord::Recor…ActiveRecord::RecordInvalid: Validation failed — Rails: ActiveRecord::RecordInvalid: Validation failed: Email can't be blank, Name is too short (Ruby / Rails)ActiveRecord::Recor…PG::UndefinedTable: relation does not exist — Rails: ActiveRecord::StatementInvalid: PG::UndefinedTable: ERROR: relation "users" does not exist (Ruby / Rails)PG::UndefinedTable:…NameError: uninitialized constant — Ruby: NameError: uninitialized constant UsersController::User (Did you mean? Users) (Ruby / Rails)NameError: uninitia…NameError: undefined local variable or method — Ruby: NameError: undefined local variable or method 'x' for main:Object (Ruby / Rails)NameError: undefine…Mysql2::Error: Unknown column in field list — Rails: ActiveRecord::StatementInvalid: Mysql2::Error: Unknown column 'users.nickname' in 'field list' (Ruby / Rails)Mysql2::Error: Unkn…ActiveRecord::PendingMigrationError — Rails: ActiveRecord::PendingMigrationError — Migrations are pending. To resolve this issue, run: bin/rails db:migrate (Ruby / Rails)ActiveRecord::Pendi…ActiveRecord::RecordNotUnique: duplicate key value — Rails: ActiveRecord::RecordNotUnique: PG::UniqueViolation: ERROR: duplicate key value violates unique constraint "index_users_on_email" (Ruby / Rails)ActiveRecord::Recor…PG::DuplicateColumn / Duplicate column name (migration) — Rails: ActiveRecord::StatementInvalid: PG::DuplicateColumn: ERROR: column "status" of relation "orders" already exists (Ruby / Rails)PG::DuplicateColumn…

Directly related (7)

CORS blocked (Laravel API)Laravel

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.

CORS error calling Next.js API route / route handlerNext.js

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.

ActiveRecord::IrreversibleMigrationRuby / Rails

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.

ActiveRecord::ConnectionNotEstablishedRuby / Rails

Rails: ActiveRecord::ConnectionNotEstablished: No connection pool for 'ActiveRecord::Base' found

ActiveRecord has no database connection configured or established for this process.

PG::ConnectionBad: could not connect to serverRuby / Rails

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.

ActiveRecord::Deadlocked: PG::TRDeadlockDetectedRuby / Rails

Rails: ActiveRecord::Deadlocked: PG::TRDeadlockDetected: ERROR: deadlock detected

Two transactions locked rows in opposite orders, so PostgreSQL aborted one.

ActiveRecord::AssociationTypeMismatchRuby / Rails

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.

Two steps away (21)

Attempt to read property "x" on nullLaravel

Laravel/PHP 8: ErrorException: Attempt to read property "name" on null

You accessed a property on a value that is `null`, typically an empty relationship or a query that found nothing.

429 Too Many Requests (Laravel throttle)Laravel

Laravel: Illuminate\Http\Exceptions\ThrottleRequestsException: Too Many Attempts. / 429 Too Many Requests

Laravel's rate limiter blocked the client for exceeding the allowed requests per minute.

Sanctum: 401 UnauthenticatedLaravel

Laravel Sanctum: {"message":"Unauthenticated."} 401 on API / SPA requests

A request to a `auth:sanctum` route had no valid token or session, so Laravel returned 401.

Hydration error: <div> cannot be a descendant of <p>Next.js

Next.js: Warning: validateDOMNesting(...): <div> cannot appear as a descendant of <p> / In HTML, <p> cannot be a descendant of <p>. This will cause a hydration error

The rendered HTML has an invalid element nesting, so the browser "fixes" it and React's hydration no longer matches.

createContext only works in Client ComponentsNext.js

Next.js: You're importing a component that needs createContext. It only works in a Client Component but none of its parents are marked with "use client"

A context provider (or a lib that uses `createContext`) is used in a Server Component.

Route used params.x — params should be awaitedNext.js

Next.js 15: Error: Route "/blog/[slug]" used `params.slug`. `params` should be awaited before using its properties

In Next.js 15 `params` and `searchParams` are Promises; reading properties synchronously triggers this error/warning.

1146MySQL

MySQL ERROR 1146 (42S02): Table 'db.table' doesn't exist

The query references a table that MySQL can’t find in that database.

42P01PostgreSQL

PostgreSQL: ERROR: relation "x" does not exist

The table/view isn’t found — missing migration, wrong schema, or a case-sensitive quoted name.

1022MySQL

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.

ActionController::InvalidAuthenticityTokenRuby / Rails

Rails: ActionController::InvalidAuthenticityToken (Can't verify CSRF token authenticity)

A non-GET request arrived without a valid CSRF token for the session.

Error: connect ECONNREFUSED 127.0.0.1:6379Redis

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.

Redis TLS: SSL handshake error / protocol mismatchRedis

Redis: Error: write EPROTO ... SSL routines:ssl3_get_record:wrong version number / Connection reset by peer (TLS vs plaintext)

The client and server disagree about TLS — plaintext client to a TLS port, or TLS client to a plaintext port.

ActiveRecord::RecordNotFound: Couldn't find X with 'id'=Ruby / Rails

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).

ActiveRecord::RecordInvalid: Validation failedRuby / Rails

Rails: ActiveRecord::RecordInvalid: Validation failed: Email can't be blank, Name is too short

`save!`/`create!`/`update!` raised because validations failed.

PG::UndefinedTable: relation does not existRuby / Rails

Rails: ActiveRecord::StatementInvalid: PG::UndefinedTable: ERROR: relation "users" does not exist

Rails queried a table that isn't in the connected PostgreSQL database.

NameError: uninitialized constantRuby / Rails

Ruby: NameError: uninitialized constant UsersController::User (Did you mean? Users)

Ruby (or Rails autoloading) couldn't find a class or module with that name in the current scope.

NameError: undefined local variable or methodRuby / Rails

Ruby: NameError: undefined local variable or method 'x' for main:Object

Ruby saw a bare identifier that is neither a local variable nor a method on the current object.

Mysql2::Error: Unknown column in field listRuby / Rails

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).

ActiveRecord::PendingMigrationErrorRuby / Rails

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.

ActiveRecord::RecordNotUnique: duplicate key valueRuby / Rails

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.

PG::DuplicateColumn / Duplicate column name (migration)Ruby / Rails

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.

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