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Active Record Relation

Namespace
Methods
#
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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]
 
SINGLE_VALUE_METHODS = [:limit, :offset, :lock, :readonly, :reordering, :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
  @offsets = {}
  @loaded = false
  @predicate_builder = predicate_builder
  @delegate_to_klass = false
end
Instance Public methods
==(other)

Compares two relations for equality.

# File activerecord/lib/active_record/relation.rb, line 566
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 257
def any?
  return super if block_given?
  !empty?
end
blank?()

Returns true if relation is blank.

# File activerecord/lib/active_record/relation.rb, line 582
def blank?
  records.blank?
end
build(attributes = nil, &block)
Alias for: new
cache_key(timestamp_column = :updated_at)

Returns a cache key that can be used to identify the records fetched by this query. The cache key is built with a fingerprint of the sql query, the number of records matched by the query and a 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 key changes.

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

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%')

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)

You can customize the strategy to generate the key on a per model basis overriding ActiveRecord::Base#collection_cache_key.

# File activerecord/lib/active_record/relation.rb, line 295
def cache_key(timestamp_column = :updated_at)
  @cache_keys ||= {}
  @cache_keys[timestamp_column] ||= @klass.collection_cache_key(self, timestamp_column)
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 89
def create(attributes = nil, &block)
  scoping { klass.create(attributes, &block) }
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 99
def create!(attributes = nil, &block)
  scoping { klass.create!(attributes, &block) }
end
create_or_find_by(attributes, &block)

Attempts to create a record with the given attributes in a table that has a unique 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 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.

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 189
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 198
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 466
def delete_all
  invalid_methods = INVALID_METHODS_FOR_DELETE_ALL.select do |method|
    value = get_value(method)
    SINGLE_VALUE_METHODS.include?(method) ? value : value.any?
  end
  if invalid_methods.any?
    raise ActiveRecordError.new("delete_all doesn't support #{invalid_methods.join(', ')}")
  end

  if eager_loading?
    relation = apply_join_dependency
    return relation.delete_all
  end

  stmt = Arel::DeleteManager.new
  stmt.from(arel.join_sources.empty? ? table : arel.source)
  stmt.key = arel_attribute(primary_key)
  stmt.take(arel.limit)
  stmt.offset(arel.offset)
  stmt.order(*arel.orders)
  stmt.wheres = arel.constraints

  affected = @klass.connection.delete(stmt, "#{@klass} Destroy")

  reset
  affected
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 444
def destroy_all
  records.each(&:destroy).tap { reset }
end
eager_loading?()

Returns true if relation needs eager loading.

# File activerecord/lib/active_record/relation.rb, line 551
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 245
def empty?
  return @records.empty? if loaded?
  !exists?
end
encode_with(coder)

Serializes the relation objects Array.

# File activerecord/lib/active_record/relation.rb, line 235
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 219
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
# different 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 152
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 159
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 206
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 37
def initialize_copy(other)
  @values = @values.dup
  reset
end
inspect()
# File activerecord/lib/active_record/relation.rb, line 590
def inspect
  subject = loaded? ? records : self
  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 561
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 500
def load(&block)
  exec_queries(&block) unless loaded?

  self
end
many?()

Returns true if there is more than one record.

# File activerecord/lib/active_record/relation.rb, line 269
def many?
  return super if block_given?
  limit_value ? records.many? : size > 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 64
def new(attributes = nil, &block)
  scoping { klass.new(attributes, &block) }
end
none?()

Returns true if there are no records.

# File activerecord/lib/active_record/relation.rb, line 251
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 263
def one?
  return super if block_given?
  limit_value ? records.one? : size == 1
end
pretty_print(q)
# File activerecord/lib/active_record/relation.rb, line 577
def pretty_print(q)
  q.pp(records)
end
reload()

Forces reloading of relation.

# File activerecord/lib/active_record/relation.rb, line 507
def reload
  reset
  load
end
reset()
# File activerecord/lib/active_record/relation.rb, line 512
def reset
  @delegate_to_klass = false
  @to_sql = @arel = @loaded = @should_eager_load = nil
  @records = [].freeze
  @offsets = {}
  self
end
scope_for_create()
# File activerecord/lib/active_record/relation.rb, line 546
def scope_for_create
  where_values_hash.merge!(create_with_value.stringify_keys)
end
scoping()

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

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 309
def scoping
  @delegate_to_klass ? yield : klass._scoping(self) { yield }
end
size()

Returns size of the records.

# File activerecord/lib/active_record/relation.rb, line 240
def size
  loaded? ? @records.length : count(:all)
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 224
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 524
def to_sql
  @to_sql ||= begin
    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
end
touch_all(*names, time: nil)

Touches all records in the current relation without instantiating records first with the updated_at/on attributes set to the current time or the time specified. This method can be passed attribute names and an optional time argument. If attribute names are passed, they are updated along with updated_at/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 419
def touch_all(*names, time: nil)
  if klass.locking_enabled?
    names << { time: time }
    update_counters(klass.locking_column => 1, touch: names)
  else
    update_all klass.touch_attributes_with_time(*names, time: time)
  end
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.

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 342
def update_all(updates)
  raise ArgumentError, "Empty list of attributes to change" if updates.blank?

  if eager_loading?
    relation = apply_join_dependency
    return relation.update_all(updates)
  end

  stmt = Arel::UpdateManager.new
  stmt.table(arel.join_sources.empty? ? table : arel.source)
  stmt.key = arel_attribute(primary_key)
  stmt.take(arel.limit)
  stmt.offset(arel.offset)
  stmt.order(*arel.orders)
  stmt.wheres = arel.constraints

  if updates.is_a?(Hash)
    stmt.set _substitute_values(updates)
  else
    stmt.set Arel.sql(klass.sanitize_sql_for_assignment(updates, table.name))
  end

  @klass.connection.update stmt, "#{@klass} Update All"
end
values()
# File activerecord/lib/active_record/relation.rb, line 586
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 542
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 624
def load_records(records)
  @records = records.freeze
  @loaded = true
end