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Active Record Relation

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Included Modules

Constants

CLAUSE_METHODS = [:where, :having, :from]
 
INVALID_METHODS_FOR_DELETE_ALL = [:distinct, :group, :having]
 
MULTI_VALUE_METHODS = [:includes, :eager_load, :preload, :select, :group, :order, :joins, :left_outer_joins, :references, :extending, :unscope, :optimizer_hints, :annotate]
 
SINGLE_VALUE_METHODS = [:limit, :offset, :lock, :readonly, :reordering, :strict_loading, :reverse_order, :distinct, :create_with, :skip_query_cache]
 
VALUE_METHODS = MULTI_VALUE_METHODS + SINGLE_VALUE_METHODS + CLAUSE_METHODS
 

Attributes

[R] klass
[R] loaded
[R] loaded?
[R] model
[R] predicate_builder
[RW] skip_preloading_value
[R] table

Class Public methods

new(klass, table: klass.arel_table, predicate_builder: klass.predicate_builder, values: {})

# File activerecord/lib/active_record/relation.rb, line 27
def initialize(klass, table: klass.arel_table, predicate_builder: klass.predicate_builder, values: {})
  @klass  = klass
  @table  = table
  @values = values
  @loaded = false
  @predicate_builder = predicate_builder
  @delegate_to_klass = false
  @future_result = nil
  @records = nil
  @limited_count = nil
end

Instance Public methods

==(other)

Compares two relations for equality.

# File activerecord/lib/active_record/relation.rb, line 754
def ==(other)
  case other
  when Associations::CollectionProxy, AssociationRelation
    self == other.records
  when Relation
    other.to_sql == to_sql
  when Array
    records == other
  end
end

any?()

Returns true if there are any records.

# File activerecord/lib/active_record/relation.rb, line 290
def any?
  return super if block_given?
  !empty?
end

blank?()

Returns true if relation is blank.

# File activerecord/lib/active_record/relation.rb, line 770
def blank?
  records.blank?
end

build(attributes = nil, &block)

Alias for: new

cache_key(timestamp_column = "updated_at")

Returns a stable cache key that can be used to identify this query. The cache key is built with a fingerprint of the SQL query.

Product.where("name like ?", "%Cosmic Encounter%").cache_key
# => "products/query-1850ab3d302391b85b8693e941286659"

If ActiveRecord::Base.collection_cache_versioning is turned off, as it was in Rails 6.0 and earlier, the cache key will also include a version.

ActiveRecord::Base.collection_cache_versioning = false
Product.where("name like ?", "%Cosmic Encounter%").cache_key
# => "products/query-1850ab3d302391b85b8693e941286659-1-20150714212553907087000"

You can also pass a custom timestamp column to fetch the timestamp of the last updated record.

Product.where("name like ?", "%Game%").cache_key(:last_reviewed_at)
# File activerecord/lib/active_record/relation.rb, line 326
def cache_key(timestamp_column = "updated_at")
  @cache_keys ||= {}
  @cache_keys[timestamp_column] ||= klass.collection_cache_key(self, timestamp_column)
end

cache_key_with_version()

Returns a cache key along with the version.

# File activerecord/lib/active_record/relation.rb, line 405
def cache_key_with_version
  if version = cache_version
    "#{cache_key}-#{version}"
  else
    cache_key
  end
end

cache_version(timestamp_column = :updated_at)

Returns a cache version that can be used together with the cache key to form a recyclable caching scheme. The cache version is built with the number of records matching the query, and the timestamp of the last updated record. When a new record comes to match the query, or any of the existing records is updated or deleted, the cache version changes.

If the collection is loaded, the method will iterate through the records to generate the timestamp, otherwise it will trigger one SQL query like:

SELECT COUNT(*), MAX("products"."updated_at") FROM "products" WHERE (name like '%Cosmic Encounter%')
# File activerecord/lib/active_record/relation.rb, line 353
def cache_version(timestamp_column = :updated_at)
  if collection_cache_versioning
    @cache_versions ||= {}
    @cache_versions[timestamp_column] ||= compute_cache_version(timestamp_column)
  end
end

create(attributes = nil, &block)

Tries to create a new record with the same scoped attributes defined in the relation. Returns the initialized object if validation fails.

Expects arguments in the same format as ActiveRecord::Base.create.

Examples

users = User.where(name: 'Oscar')
users.create # => #<User id: 3, name: "Oscar", ...>

users.create(name: 'fxn')
users.create # => #<User id: 4, name: "fxn", ...>

users.create { |user| user.name = 'tenderlove' }
# => #<User id: 5, name: "tenderlove", ...>

users.create(name: nil) # validation on name
# => #<User id: nil, name: nil, ...>
# File activerecord/lib/active_record/relation.rb, line 101
def create(attributes = nil, &block)
  if attributes.is_a?(Array)
    attributes.collect { |attr| create(attr, &block) }
  else
    block = current_scope_restoring_block(&block)
    scoping { _create(attributes, &block) }
  end
end

create!(attributes = nil, &block)

Similar to create, but calls create! on the base class. Raises an exception if a validation error occurs.

Expects arguments in the same format as ActiveRecord::Base.create!.

# File activerecord/lib/active_record/relation.rb, line 116
def create!(attributes = nil, &block)
  if attributes.is_a?(Array)
    attributes.collect { |attr| create!(attr, &block) }
  else
    block = current_scope_restoring_block(&block)
    scoping { _create!(attributes, &block) }
  end
end

create_or_find_by(attributes, &block)

Attempts to create a record with the given attributes in a table that has a unique database constraint on one or several of its columns. If a row already exists with one or several of these unique constraints, the exception such an insertion would normally raise is caught, and the existing record with those attributes is found using find_by!.

This is similar to find_or_create_by, but avoids the problem of stale reads between the SELECT and the INSERT, as that method needs to first query the table, then attempt to insert a row if none is found.

There are several drawbacks to create_or_find_by, though:

  • The underlying table must have the relevant columns defined with unique database constraints.

  • A unique constraint violation may be triggered by only one, or at least less than all, of the given attributes. This means that the subsequent find_by! may fail to find a matching record, which will then raise an ActiveRecord::RecordNotFound exception, rather than a record with the given attributes.

  • While we avoid the race condition between SELECT -> INSERT from find_or_create_by, we actually have another race condition between INSERT -> SELECT, which can be triggered if a DELETE between those two statements is run by another client. But for most applications, that's a significantly less likely condition to hit.

  • It relies on exception handling to handle control flow, which may be marginally slower.

  • The primary key may auto-increment on each create, even if it fails. This can accelerate the problem of running out of integers, if the underlying table is still stuck on a primary key of type int (note: All Rails apps since 5.1+ have defaulted to bigint, which is not liable to this problem).

This method will return a record if all given attributes are covered by unique constraints (unless the INSERT -> DELETE -> SELECT race condition is triggered), but if creation was attempted and failed due to validation errors it won't be persisted, you get what create returns in such situation.

# File activerecord/lib/active_record/relation.rb, line 215
def create_or_find_by(attributes, &block)
  transaction(requires_new: true) { create(attributes, &block) }
rescue ActiveRecord::RecordNotUnique
  find_by!(attributes)
end

create_or_find_by!(attributes, &block)

Like create_or_find_by, but calls create! so an exception is raised if the created record is invalid.

# File activerecord/lib/active_record/relation.rb, line 224
def create_or_find_by!(attributes, &block)
  transaction(requires_new: true) { create!(attributes, &block) }
rescue ActiveRecord::RecordNotUnique
  find_by!(attributes)
end

delete_all()

Deletes the records without instantiating the records first, and hence not calling the #destroy method nor invoking callbacks. This is a single SQL DELETE statement that goes straight to the database, much more efficient than destroy_all. Be careful with relations though, in particular :dependent rules defined on associations are not honored. Returns the number of rows affected.

Post.where(person_id: 5).where(category: ['Something', 'Else']).delete_all

Both calls delete the affected posts all at once with a single DELETE statement. If you need to destroy dependent associations or call your before_* or after_destroy callbacks, use the destroy_all method instead.

If an invalid method is supplied, delete_all raises an ActiveRecordError:

Post.distinct.delete_all
# => ActiveRecord::ActiveRecordError: delete_all doesn't support distinct
# File activerecord/lib/active_record/relation.rb, line 606
def delete_all
  invalid_methods = INVALID_METHODS_FOR_DELETE_ALL.select do |method|
    value = @values[method]
    method == :distinct ? value : value&.any?
  end
  if invalid_methods.any?
    raise ActiveRecordError.new("delete_all doesn't support #{invalid_methods.join(', ')}")
  end

  arel = eager_loading? ? apply_join_dependency.arel : build_arel
  arel.source.left = table

  stmt = arel.compile_delete(table[primary_key])

  klass.connection.delete(stmt, "#{klass} Delete All").tap { reset }
end

delete_by(*args)

Finds and deletes all records matching the specified conditions. This is short-hand for relation.where(condition).delete_all. Returns the number of rows affected.

If no record is found, returns 0 as zero rows were affected.

Person.delete_by(id: 13)
Person.delete_by(name: 'Spartacus', rating: 4)
Person.delete_by("published_at < ?", 2.weeks.ago)
# File activerecord/lib/active_record/relation.rb, line 645
def delete_by(*args)
  where(*args).delete_all
end

destroy_all()

Destroys the records by instantiating each record and calling its #destroy method. Each object's callbacks are executed (including :dependent association options). Returns the collection of objects that were destroyed; each will be frozen, to reflect that no changes should be made (since they can't be persisted).

Note: Instantiation, callback execution, and deletion of each record can be time consuming when you're removing many records at once. It generates at least one SQL DELETE query per record (or possibly more, to enforce your callbacks). If you want to delete many rows quickly, without concern for their associations or callbacks, use delete_all instead.

Examples

Person.where(age: 0..18).destroy_all
# File activerecord/lib/active_record/relation.rb, line 584
def destroy_all
  records.each(&:destroy).tap { reset }
end

destroy_by(*args)

Finds and destroys all records matching the specified conditions. This is short-hand for relation.where(condition).destroy_all. Returns the collection of objects that were destroyed.

If no record is found, returns empty array.

Person.destroy_by(id: 13)
Person.destroy_by(name: 'Spartacus', rating: 4)
Person.destroy_by("published_at < ?", 2.weeks.ago)
# File activerecord/lib/active_record/relation.rb, line 632
def destroy_by(*args)
  where(*args).destroy_all
end

eager_loading?()

Returns true if relation needs eager loading.

# File activerecord/lib/active_record/relation.rb, line 739
def eager_loading?
  @should_eager_load ||=
    eager_load_values.any? ||
    includes_values.any? && (joined_includes_values.any? || references_eager_loaded_tables?)
end

empty?()

Returns true if there are no records.

# File activerecord/lib/active_record/relation.rb, line 275
def empty?
  if loaded?
    records.empty?
  else
    !exists?
  end
end

encode_with(coder)

Serializes the relation objects Array.

# File activerecord/lib/active_record/relation.rb, line 261
def encode_with(coder)
  coder.represent_seq(nil, records)
end

explain()

Runs EXPLAIN on the query or queries triggered by this relation and returns the result as a string. The string is formatted imitating the ones printed by the database shell.

Note that this method actually runs the queries, since the results of some are needed by the next ones when eager loading is going on.

Please see further details in the Active Record Query Interface guide.

# File activerecord/lib/active_record/relation.rb, line 245
def explain
  exec_explain(collecting_queries_for_explain { exec_queries })
end

find_or_create_by(attributes, &block)

Finds the first record with the given attributes, or creates a record with the attributes if one is not found:

# Find the first user named "Penélope" or create a new one.
User.find_or_create_by(first_name: 'Penélope')
# => #<User id: 1, first_name: "Penélope", last_name: nil>

# Find the first user named "Penélope" or create a new one.
# We already have one so the existing record will be returned.
User.find_or_create_by(first_name: 'Penélope')
# => #<User id: 1, first_name: "Penélope", last_name: nil>

# Find the first user named "Scarlett" or create a new one with
# a particular last name.
User.create_with(last_name: 'Johansson').find_or_create_by(first_name: 'Scarlett')
# => #<User id: 2, first_name: "Scarlett", last_name: "Johansson">

This method accepts a block, which is passed down to create. The last example above can be alternatively written this way:

# Find the first user named "Scarlett" or create a new one with a
# particular last name.
User.find_or_create_by(first_name: 'Scarlett') do |user|
  user.last_name = 'Johansson'
end
# => #<User id: 2, first_name: "Scarlett", last_name: "Johansson">

This method always returns a record, but if creation was attempted and failed due to validation errors it won't be persisted, you get what create returns in such situation.

Please note this method is not atomic, it runs first a SELECT, and if there are no results an INSERT is attempted. If there are other threads or processes there is a race condition between both calls and it could be the case that you end up with two similar records.

If this might be a problem for your application, please see create_or_find_by.

# File activerecord/lib/active_record/relation.rb, line 174
def find_or_create_by(attributes, &block)
  find_by(attributes) || create(attributes, &block)
end

find_or_create_by!(attributes, &block)

Like find_or_create_by, but calls create! so an exception is raised if the created record is invalid.

# File activerecord/lib/active_record/relation.rb, line 181
def find_or_create_by!(attributes, &block)
  find_by(attributes) || create!(attributes, &block)
end

find_or_initialize_by(attributes, &block)

Like find_or_create_by, but calls new instead of create.

# File activerecord/lib/active_record/relation.rb, line 232
def find_or_initialize_by(attributes, &block)
  find_by(attributes) || new(attributes, &block)
end

initialize_copy(other)

# File activerecord/lib/active_record/relation.rb, line 39
def initialize_copy(other)
  @values = @values.dup
  reset
end

inspect()

# File activerecord/lib/active_record/relation.rb, line 782
def inspect
  subject = loaded? ? records : annotate("loading for inspect")
  entries = subject.take([limit_value, 11].compact.min).map!(&:inspect)

  entries[10] = "..." if entries.size == 11

  "#<#{self.class.name} [#{entries.join(', ')}]>"
end

joined_includes_values()

Joins that are also marked for preloading. In which case we should just eager load them. Note that this is a naive implementation because we could have strings and symbols which represent the same association, but that aren't matched by this. Also, we could have nested hashes which partially match, e.g. { a: :b } & { a: [:b, :c] }

# File activerecord/lib/active_record/relation.rb, line 749
def joined_includes_values
  includes_values & joins_values
end

load(&block)

Causes the records to be loaded from the database if they have not been loaded already. You can use this if for some reason you need to explicitly load some records before actually using them. The return value is the relation itself, not the records.

Post.where(published: true).load # => #<ActiveRecord::Relation>
# File activerecord/lib/active_record/relation.rb, line 681
def load(&block)
  if !loaded? || scheduled?
    @records = exec_queries(&block)
    @loaded = true
  end

  self
end

load_async()

Schedule the query to be performed from a background thread pool.

Post.where(published: true).load_async # => #<ActiveRecord::Relation>
# File activerecord/lib/active_record/relation.rb, line 652
def load_async
  return load if !connection.async_enabled?

  unless loaded?
    result = exec_main_query(async: connection.current_transaction.closed?)

    if result.is_a?(Array)
      @records = result
    else
      @future_result = result
    end
    @loaded = true
  end

  self
end

many?()

Returns true if there is more than one record.

# File activerecord/lib/active_record/relation.rb, line 303
def many?
  return super if block_given?
  return records.many? if limit_value || loaded?
  limited_count > 1
end

new(attributes = nil, &block)

Initializes new record from relation while maintaining the current scope.

Expects arguments in the same format as ActiveRecord::Base.new.

users = User.where(name: 'DHH')
user = users.new # => #<User id: nil, name: "DHH", created_at: nil, updated_at: nil>

You can also pass a block to new with the new record as argument:

user = users.new { |user| user.name = 'Oscar' }
user.name # => Oscar
Also aliased as: build
# File activerecord/lib/active_record/relation.rb, line 72
def new(attributes = nil, &block)
  if attributes.is_a?(Array)
    attributes.collect { |attr| new(attr, &block) }
  else
    block = current_scope_restoring_block(&block)
    scoping { _new(attributes, &block) }
  end
end

none?()

Returns true if there are no records.

# File activerecord/lib/active_record/relation.rb, line 284
def none?
  return super if block_given?
  empty?
end

one?()

Returns true if there is exactly one record.

# File activerecord/lib/active_record/relation.rb, line 296
def one?
  return super if block_given?
  return records.one? if limit_value || loaded?
  limited_count == 1
end

pretty_print(q)

# File activerecord/lib/active_record/relation.rb, line 765
def pretty_print(q)
  q.pp(records)
end

reload()

Forces reloading of relation.

# File activerecord/lib/active_record/relation.rb, line 691
def reload
  reset
  load
end

reset()

# File activerecord/lib/active_record/relation.rb, line 696
def reset
  @future_result&.cancel
  @future_result = nil
  @delegate_to_klass = false
  @to_sql = @arel = @loaded = @should_eager_load = nil
  @offsets = @take = nil
  @cache_keys = nil
  @records = nil
  @limited_count = nil
  self
end

scheduled?()

Returns true if the relation was scheduled on the background thread pool.

# File activerecord/lib/active_record/relation.rb, line 671
def scheduled?
  !!@future_result
end

scope_for_create()

# File activerecord/lib/active_record/relation.rb, line 732
def scope_for_create
  hash = where_clause.to_h(klass.table_name, equality_only: true)
  create_with_value.each { |k, v| hash[k.to_s] = v } unless create_with_value.empty?
  hash
end

scoping(all_queries: nil, &block)

Scope all queries to the current scope.

Comment.where(post_id: 1).scoping do
  Comment.first
end
# => SELECT "comments".* FROM "comments" WHERE "comments"."post_id" = 1 ORDER BY "comments"."id" ASC LIMIT 1

If all_queries: true is passed, scoping will apply to all queries for the relation including update and delete on instances. Once all_queries is set to true it cannot be set to false in a nested block.

Please check unscoped if you want to remove all previous scopes (including the default_scope) during the execution of a block.

# File activerecord/lib/active_record/relation.rb, line 427
def scoping(all_queries: nil, &block)
  registry = klass.scope_registry
  if global_scope?(registry) && all_queries == false
    raise ArgumentError, "Scoping is set to apply to all queries and cannot be unset in a nested block."
  elsif already_in_scope?(registry)
    yield
  else
    _scoping(self, registry, all_queries, &block)
  end
end

size()

Returns size of the records.

# File activerecord/lib/active_record/relation.rb, line 266
def size
  if loaded?
    records.length
  else
    count(:all)
  end
end

to_a()

Alias for: to_ary

to_ary()

Converts relation objects to Array.

Also aliased as: to_a
# File activerecord/lib/active_record/relation.rb, line 250
def to_ary
  records.dup
end

to_sql()

Returns sql statement for the relation.

User.where(name: 'Oscar').to_sql
# => SELECT "users".* FROM "users"  WHERE "users"."name" = 'Oscar'
# File activerecord/lib/active_record/relation.rb, line 712
def to_sql
  @to_sql ||= if eager_loading?
    apply_join_dependency do |relation, join_dependency|
      relation = join_dependency.apply_column_aliases(relation)
      relation.to_sql
    end
  else
    conn = klass.connection
    conn.unprepared_statement { conn.to_sql(arel) }
  end
end

touch_all(*names, time: nil)

Touches all records in the current relation, setting the updated_at/updated_on attributes to the current time or the time specified. It does not instantiate the involved models, and it does not trigger Active Record callbacks or validations. This method can be passed attribute names and an optional time argument. If attribute names are passed, they are updated along with updated_at/updated_on attributes. If no time argument is passed, the current time is used as default.

Examples

# Touch all records
Person.all.touch_all
# => "UPDATE \"people\" SET \"updated_at\" = '2018-01-04 22:55:23.132670'"

# Touch multiple records with a custom attribute
Person.all.touch_all(:created_at)
# => "UPDATE \"people\" SET \"updated_at\" = '2018-01-04 22:55:23.132670', \"created_at\" = '2018-01-04 22:55:23.132670'"

# Touch multiple records with a specified time
Person.all.touch_all(time: Time.new(2020, 5, 16, 0, 0, 0))
# => "UPDATE \"people\" SET \"updated_at\" = '2020-05-16 00:00:00'"

# Touch records with scope
Person.where(name: 'David').touch_all
# => "UPDATE \"people\" SET \"updated_at\" = '2018-01-04 22:55:23.132670' WHERE \"people\".\"name\" = 'David'"
# File activerecord/lib/active_record/relation.rb, line 564
def touch_all(*names, time: nil)
  update_all klass.touch_attributes_with_time(*names, time: time)
end

update_all(updates)

Updates all records in the current relation with details given. This method constructs a single SQL UPDATE statement and sends it straight to the database. It does not instantiate the involved models and it does not trigger Active Record callbacks or validations. However, values passed to update_all will still go through Active Record's normal type casting and serialization. Returns the number of rows affected.

Note: As Active Record callbacks are not triggered, this method will not automatically update updated_at/updated_on columns.

Parameters

  • updates - A string, array, or hash representing the SET part of an SQL statement.

Examples

# Update all customers with the given attributes
Customer.update_all wants_email: true

# Update all books with 'Rails' in their title
Book.where('title LIKE ?', '%Rails%').update_all(author: 'David')

# Update all books that match conditions, but limit it to 5 ordered by date
Book.where('title LIKE ?', '%Rails%').order(:created_at).limit(5).update_all(author: 'David')

# Update all invoices and set the number column to its id value.
Invoice.update_all('number = id')
# File activerecord/lib/active_record/relation.rb, line 470
def update_all(updates)
  raise ArgumentError, "Empty list of attributes to change" if updates.blank?

  if updates.is_a?(Hash)
    if klass.locking_enabled? &&
        !updates.key?(klass.locking_column) &&
        !updates.key?(klass.locking_column.to_sym)
      attr = table[klass.locking_column]
      updates[attr.name] = _increment_attribute(attr)
    end
    values = _substitute_values(updates)
  else
    values = Arel.sql(klass.sanitize_sql_for_assignment(updates, table.name))
  end

  arel = eager_loading? ? apply_join_dependency.arel : build_arel
  arel.source.left = table

  stmt = arel.compile_update(values, table[primary_key])

  klass.connection.update(stmt, "#{klass} Update All").tap { reset }
end

update_counters(counters)

Updates the counters of the records in the current relation.

Parameters

  • counter - A Hash containing the names of the fields to update as keys and the amount to update as values.

  • :touch option - Touch the timestamp columns when updating.

  • If attributes names are passed, they are updated along with update_at/on attributes.

Examples

# For Posts by a given author increment the comment_count by 1.
Post.where(author_id: author.id).update_counters(comment_count: 1)
# File activerecord/lib/active_record/relation.rb, line 521
def update_counters(counters)
  touch = counters.delete(:touch)

  updates = {}
  counters.each do |counter_name, value|
    attr = table[counter_name]
    updates[attr.name] = _increment_attribute(attr, value)
  end

  if touch
    names = touch if touch != true
    names = Array.wrap(names)
    options = names.extract_options!
    touch_updates = klass.touch_attributes_with_time(*names, **options)
    updates.merge!(touch_updates) unless touch_updates.empty?
  end

  update_all updates
end

values()

# File activerecord/lib/active_record/relation.rb, line 774
def values
  @values.dup
end

where_values_hash(relation_table_name = klass.table_name)

Returns a hash of where conditions.

User.where(name: 'Oscar').where_values_hash
# => {name: "Oscar"}
# File activerecord/lib/active_record/relation.rb, line 728
def where_values_hash(relation_table_name = klass.table_name)
  where_clause.to_h(relation_table_name)
end

Instance Protected methods

load_records(records)

# File activerecord/lib/active_record/relation.rb, line 823
def load_records(records)
  @records = records.freeze
  @loaded = true
end