Step 3 / Select topic Rails Hard

What this bank covers

• where.not and NULL columns
• sum on an empty relation
• last on a limited relation
• joins produces duplicate parent rows
• Combining conditions with or
• count(*) versus count(column)
• find_by versus find_by!
• update_all bypasses validations
• group with sum and NULL values
• size versus count on relations
• dependent: :nullify on has_many
• inverse_of shares the owner object
• has_many :through returns one row per join row
• Replacing a has_one nullifies the old record
• dependent on the join model only removes join rows
• Self-referential has_many
• Appending to a has_many on an unsaved parent
• Polymorphic has_many filters on type too
• Association scopes seed attributes on create
• belongs_to touch: true
• Callback order on create
• valid? triggers validation callbacks
• Returning false no longer halts a callback chain
• Multiple validators on one attribute
• save(validate: false) skips validations only
• Full messages prepend the humanized attribute
• Save callbacks are skipped when validation fails
• update_column bypasses callbacks and validations
• throw :abort halts destroy
• The on: :create validation context
• column_names after t.timestamps
• create_table id: false
• Typed column defaults
• Decimal columns cast to BigDecimal
• reset_column_information
• t.references column naming
• t.timestamps and NOT NULL
• String column limit in the schema
• Custom primary key in create_table
• Default index names
• with_indifferent_access is deep
• in_groups_of without padding
• Adding a month duration to a date
• String#truncate counts the omission
• Object#blank? and zero
• to_sentence connectors
• Inflector rules for -sis words
• Hash#deep_merge
• Integer#ordinalize and the teens
• ActiveSupport::Concern included and class_methods blocks
• Polynomial backoff waits
• Non-idempotent job body
• Priority then enqueue order
• Database-level job deduplication
• Attempts count total executions
• Enqueuing inside a rolled-back transaction
• Deserializing a deleted record
• wait versus wait_until
• Atomic claiming with update_all
• Serialized job arguments lose symbols
• MessageVerifier rejects tampered tokens
• fixed_length_secure_compare demands equal lengths
• Bind placeholders quote user input
• sanitize_sql_like neutralises wildcards
• Which characters html_escape replaces
• Purpose binding in MessageVerifier
• SecureRandom.hex argument is byte count
• String interpolation opens an injection hole
• ParameterFilter matches nested and partial keys
• fixed_length_secure_compare vs secure_compare
• includes preloads in a second query
• pluck selects a single column
• find_each batching math
• counter caches make size free
• partial selects and missing attributes
• update_all skips the model layer
• joins does not eager load
• eager_load builds one outer join
• pluck on a loaded relation
• the ActiveRecord query cache
• Routes created by a resourceful route
• Route order decides the winner
• Nested resource paths
• Shallow nesting
• Member versus collection routes
• path: versus as:
• Segment constraints are matched against the whole segment
• scope module: changes the controller only
• only: restricts the helpers too
• Wildcard segments and the format
• permit only keeps scalars for bare keys
• key: [] requires every element to be a scalar
• nil and empty strings are permitted scalars
• require with an array of keys
• key: {} permits an arbitrary nested hash
• permit filters each hash in an array
• permit! is recursive
• Bare keys never permit arrays
• to_unsafe_h converts deeply
• except/slice inherit permitted status