Step 3 / Select topic Rails Medium

What this bank covers

• first on an empty relation
• pluck returns a flat array
• where with a nil value
• group(...).count returns a hash
• combining conditions with or
• where.not and NULL values
• order, limit and offset together
• find_by! versus find_by
• sum and maximum on an empty relation
• joins produces one row per match
• has_many dependent: :destroy
• belongs_to optional: false
• Association size vs count
• has_many :through
• Appending with << on a has_many
• has_one foreign key location
• dependent: :nullify
• Autosaving built children
• joins duplicates and distinct
• habtm join table naming
• Create callback order
• full_messages wording
• throw :abort in before_create
• Normalizing in before_validation
• Validation contexts with on: :update
• Failed update leaves the row untouched
• Callback firing order on create
• Skipping validations with save(validate: false)
• Halting the save chain with throw :abort
• Full messages from a length validation
• Counting columns created by create_table
• Reading a NOT NULL constraint from the schema
• The type behind a references column
• rename_column replaces the old column
• Custom primary key names
• Schema defaults appear on new objects
• Column defaults from add_column
• Polymorphic references add two columns
• remove_column and the resulting column list
• Query string values are strings
• Nested parameters
• Path parameters win over query parameters
• permit filters unlisted keys
• before_action with :only
• Strong parameters protect columns
• Inflector pluralization rules
• underscore on namespaced constants
• Hash#deep_merge
• Date#advance across month ends
• String#squish
• String#titleize
• ActiveSupport::Duration inspect
• String#parameterize
• blank? and zero
• Array#in_groups_of
• Exponential backoff total wait
• Idempotency guard against duplicate delivery
• Priority ordering with FIFO tie-break
• Retries stop at the first success
• GlobalID arguments reload at perform time
• Exhausted retries land in the dead set
• Scheduled delay plus retry backoff
• Makespan of a greedy two-worker pool
• Enqueue after commit, not after create
• Unique jobs collapse repeated lock keys
• String interpolation opens a SQL injection hole
• Constant-time comparison helpers differ on length
• MessageVerifier detects tampering
• Decrypting with the wrong key
• Escaping LIKE wildcards
• Quoting values with sanitize_sql
• HTML escaping guards against XSS
• Mass assignment is unguarded at the model layer
• SecureRandom.hex counts bytes, not characters
• Expired signed messages fail verification
• includes preloads the association
• strict_loading blocks lazy association loads
• counter_cache keeps a denormalised count
• find_in_batches chunks a large table
• select narrows the attributes loaded
• any? uses an existence query
• eager_load joins in one query
• update_all bypasses validations and callbacks
• SQL aggregates on an empty relation
• insert_all batches rows into one statement
• Default index naming in migrations
• Route order inside resources
• Resourceful edit route
• Dynamic segments become params
• Dots and the format segment
• The seven resourceful actions
• Naming of resourceful path helpers
• PATCH and PUT both reach update
• Nested resource member paths
• Singular resource routes
• Route globbing with a wildcard segment
• require + permit with an array filter
• permit! marks nested parameters permitted
• [] access versus require
• Scalar filters reject array values