Error map
NameError: undefined local variable or method Ruby: NameError: undefined local variable or method 'x' for main:Object
Ruby / Rails · layer 4, Application & API
Centre: this error. First ring: errors it is linked with (9). 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 (9)
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.
Ruby: FrozenError: can't modify frozen String: "abc"
You tried to change an object that's frozen — string literals under `# frozen_string_literal: true`, constants, symbols or frozen…
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.
Ruby: ArgumentError: missing keyword: :name / unknown keyword: :nmae
A method requiring keyword arguments was called without them, or with a misspelt keyword.
Rails: ActiveRecord::Deadlocked: PG::TRDeadlockDetected: ERROR: deadlock detected
Two transactions locked rows in opposite orders, so PostgreSQL aborted one.
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.
Ruby: ArgumentError: wrong number of arguments (given 1, expected 2..3)
A method was called with more or fewer arguments than it accepts.
Rails: ActiveRecord::ConnectionNotEstablished: No connection pool for 'ActiveRecord::Base' found
ActiveRecord has no database connection configured or established for this process.
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 (25)
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: ActionController::InvalidAuthenticityToken (Can't verify CSRF token authenticity)
A non-GET request arrived without a valid CSRF token for the session.
Ruby: TypeError: no implicit conversion of nil into String
A String method (`+`, `File.join`, `Array#join` usage) received `nil` instead of a string.
Bundler: Could not find gem 'rails (~> 7.1)' in locally installed gems / Could not find rails-7.1.0 in any of the gem sources listed in your Gemfile
A gem from the Gemfile/Gemfile.lock isn't installed (or isn't available at that version).
Bundler: Bundler could not find compatible versions for gem "activesupport": In Gemfile: rails (= 7.1.0) depends on activesupport (= 7.1.0)
Two gems in your Gemfile require incompatible versions of a shared dependency.
FactoryBot: FactoryBot::DuplicateDefinitionError: Factory already registered: user
Two factory definitions use the same name (or files are loaded twice).
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.
macOS: ERROR: While executing gem ... (Gem::FilePermissionError) You don't have write permissions for the /Library/Ruby/Gems/2.6.0 directory
`gem install` tries to write into Apple's system Ruby, which is protected and shouldn't be modified.
Ruby: TypeError: nil can't be coerced into Integer / String can't be coerced into Integer
Arithmetic combined a number with `nil` (or a String) which Ruby can't convert automatically.
Ruby: LoadError: cannot load such file -- nokogiri (or: cannot load such file -- bundler/setup)
`require` couldn't find the file/gem — it isn't installed, not in the Gemfile, or the load path is wrong.
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::RecordInvalid: Validation failed: Email can't be blank, Name is too short
`save!`/`create!`/`update!` raised because validations failed.
Rails: ActiveRecord::StatementInvalid: PG::UndefinedTable: ERROR: relation "users" does not exist
Rails queried a table that isn't in the connected PostgreSQL database.
Rails: Zeitwerk::NameError: expected file app/models/user_profile.rb to define constant UserProfile, but didn't
Rails autoloading found a file whose name implies a constant the file doesn't define.
Ruby: ERROR: Failed to build gem native extension. current directory: /gems/pg-1.5.4/ext/pg — An error occurred while installing pg
A gem with C code couldn't compile, usually because a system library or header is missing.
Bundler: Your Ruby version is 3.1.2, but your Gemfile specified 3.3.0
`.ruby-version`/the Gemfile `ruby` line requires a different Ruby than the one running.
RSpec: expected: 200 got: 404 (compared using ==) — RSpec::Expectations::ExpectationNotMetError
An RSpec `expect` assertion didn't hold: the actual value differs from what the test expected.
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: 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.
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::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::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: 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.
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