module ActiveRecord::FinderMethods

Constants

ONE_AS_ONE

Public Instance Methods

exists?(conditions = :none) click to toggle source

Returns true if a record exists in the table that matches the id or conditions given, or false otherwise. The argument can take six forms:

  • Integer - Finds the record with this primary key.

  • String - Finds the record with a primary key corresponding to this string (such as '5').

  • Array - Finds the record that matches these find-style conditions (such as ['name LIKE ?', "%#{query}%"]).

  • Hash - Finds the record that matches these find-style conditions (such as {name: 'David'}).

  • false - Returns always false.

  • No args - Returns false if the table is empty, true otherwise.

For more information about specifying conditions as a hash or array, see the Conditions section in the introduction to ActiveRecord::Base.

Note: You can't pass in a condition as a string (like name = 'Jamie'), since it would be sanitized and then queried against the primary key column, like id = 'name = \'Jamie\''.

Person.exists?(5)
Person.exists?('5')
Person.exists?(['name LIKE ?', "%#{query}%"])
Person.exists?(id: [1, 4, 8])
Person.exists?(name: 'David')
Person.exists?(false)
Person.exists?
# File activerecord/lib/active_record/relation/finder_methods.rb, line 303
    def exists?(conditions = :none)
      if Base === conditions
        raise ArgumentError, <<-MSG.squish
          You are passing an instance of ActiveRecord::Base to `exists?`.
          Please pass the id of the object by calling `.id`.
        MSG
      end

      return false if !conditions || limit_value == 0

      relation = self unless eager_loading?
      relation ||= apply_join_dependency(self, construct_join_dependency(eager_loading: false))

      return false if ActiveRecord::NullRelation === relation

      relation = construct_relation_for_exists(relation, conditions)

      skip_query_cache_if_necessary { connection.select_value(relation.arel, "#{name} Exists") } ? true : false
    rescue ::RangeError
      false
    end
fifth() click to toggle source

Find the fifth record. If no order is defined it will order by primary key.

Person.fifth # returns the fifth object fetched by SELECT * FROM people
Person.offset(3).fifth # returns the fifth object from OFFSET 3 (which is OFFSET 7)
Person.where(["user_name = :u", { u: user_name }]).fifth
# File activerecord/lib/active_record/relation/finder_methods.rb, line 218
def fifth
  find_nth 4
end
fifth!() click to toggle source

Same as fifth but raises ActiveRecord::RecordNotFound if no record is found.

# File activerecord/lib/active_record/relation/finder_methods.rb, line 224
def fifth!
  fifth || raise_record_not_found_exception!
end
find(*args) click to toggle source

Find by id - This can either be a specific id (1), a list of ids (1, 5, 6), or an array of ids ([5, 6, 10]). If one or more records can not be found for the requested ids, then RecordNotFound will be raised. If the primary key is an integer, find by id coerces its arguments using to_i.

Person.find(1)          # returns the object for ID = 1
Person.find("1")        # returns the object for ID = 1
Person.find("31-sarah") # returns the object for ID = 31
Person.find(1, 2, 6)    # returns an array for objects with IDs in (1, 2, 6)
Person.find([7, 17])    # returns an array for objects with IDs in (7, 17)
Person.find([1])        # returns an array for the object with ID = 1
Person.where("administrator = 1").order("created_on DESC").find(1)

NOTE: The returned records may not be in the same order as the ids you provide since database rows are unordered. You will need to provide an explicit QueryMethods#order option if you want the results to be sorted.

Find with lock

Example for find with a lock: Imagine two concurrent transactions: each will read person.visits == 2, add 1 to it, and save, resulting in two saves of person.visits = 3. By locking the row, the second transaction has to wait until the first is finished; we get the expected person.visits == 4.

Person.transaction do
  person = Person.lock(true).find(1)
  person.visits += 1
  person.save!
end

Variations of find

Person.where(name: 'Spartacus', rating: 4)
# returns a chainable list (which can be empty).

Person.find_by(name: 'Spartacus', rating: 4)
# returns the first item or nil.

Person.find_or_initialize_by(name: 'Spartacus', rating: 4)
# returns the first item or returns a new instance (requires you call .save to persist against the database).

Person.find_or_create_by(name: 'Spartacus', rating: 4)
# returns the first item or creates it and returns it.

Alternatives for find

Person.where(name: 'Spartacus', rating: 4).exists?(conditions = :none)
# returns a boolean indicating if any record with the given conditions exist.

Person.where(name: 'Spartacus', rating: 4).select("field1, field2, field3")
# returns a chainable list of instances with only the mentioned fields.

Person.where(name: 'Spartacus', rating: 4).ids
# returns an Array of ids.

Person.where(name: 'Spartacus', rating: 4).pluck(:field1, :field2)
# returns an Array of the required fields.
Calls superclass method
# File activerecord/lib/active_record/relation/finder_methods.rb, line 66
def find(*args)
  return super if block_given?
  find_with_ids(*args)
end
find_by(arg, *args) click to toggle source

Finds the first record matching the specified conditions. There is no implied ordering so if order matters, you should specify it yourself.

If no record is found, returns nil.

Post.find_by name: 'Spartacus', rating: 4
Post.find_by "published_at < ?", 2.weeks.ago
# File activerecord/lib/active_record/relation/finder_methods.rb, line 79
def find_by(arg, *args)
  where(arg, *args).take
rescue ::RangeError
  nil
end
find_by!(arg, *args) click to toggle source

Like find_by, except that if no record is found, raises an ActiveRecord::RecordNotFound error.

# File activerecord/lib/active_record/relation/finder_methods.rb, line 87
def find_by!(arg, *args)
  where(arg, *args).take!
rescue ::RangeError
  raise RecordNotFound.new("Couldn't find #{@klass.name} with an out of range value",
                           @klass.name)
end
first(limit = nil) click to toggle source

Find the first record (or first N records if a parameter is supplied). If no order is defined it will order by primary key.

Person.first # returns the first object fetched by SELECT * FROM people ORDER BY people.id LIMIT 1
Person.where(["user_name = ?", user_name]).first
Person.where(["user_name = :u", { u: user_name }]).first
Person.order("created_on DESC").offset(5).first
Person.first(3) # returns the first three objects fetched by SELECT * FROM people ORDER BY people.id LIMIT 3
# File activerecord/lib/active_record/relation/finder_methods.rb, line 120
def first(limit = nil)
  if limit
    find_nth_with_limit(0, limit)
  else
    find_nth 0
  end
end
first!() click to toggle source

Same as first but raises ActiveRecord::RecordNotFound if no record is found. Note that first! accepts no arguments.

# File activerecord/lib/active_record/relation/finder_methods.rb, line 130
def first!
  first || raise_record_not_found_exception!
end
forty_two() click to toggle source

Find the forty-second record. Also known as accessing “the reddit”. If no order is defined it will order by primary key.

Person.forty_two # returns the forty-second object fetched by SELECT * FROM people
Person.offset(3).forty_two # returns the forty-second object from OFFSET 3 (which is OFFSET 44)
Person.where(["user_name = :u", { u: user_name }]).forty_two
# File activerecord/lib/active_record/relation/finder_methods.rb, line 234
def forty_two
  find_nth 41
end
forty_two!() click to toggle source

Same as forty_two but raises ActiveRecord::RecordNotFound if no record is found.

# File activerecord/lib/active_record/relation/finder_methods.rb, line 240
def forty_two!
  forty_two || raise_record_not_found_exception!
end
fourth() click to toggle source

Find the fourth record. If no order is defined it will order by primary key.

Person.fourth # returns the fourth object fetched by SELECT * FROM people
Person.offset(3).fourth # returns the fourth object from OFFSET 3 (which is OFFSET 6)
Person.where(["user_name = :u", { u: user_name }]).fourth
# File activerecord/lib/active_record/relation/finder_methods.rb, line 202
def fourth
  find_nth 3
end
fourth!() click to toggle source

Same as fourth but raises ActiveRecord::RecordNotFound if no record is found.

# File activerecord/lib/active_record/relation/finder_methods.rb, line 208
def fourth!
  fourth || raise_record_not_found_exception!
end
last(limit = nil) click to toggle source

Find the last record (or last N records if a parameter is supplied). If no order is defined it will order by primary key.

Person.last # returns the last object fetched by SELECT * FROM people
Person.where(["user_name = ?", user_name]).last
Person.order("created_on DESC").offset(5).last
Person.last(3) # returns the last three objects fetched by SELECT * FROM people.

Take note that in that last case, the results are sorted in ascending order:

[#<Person id:2>, #<Person id:3>, #<Person id:4>]

and not:

[#<Person id:4>, #<Person id:3>, #<Person id:2>]
# File activerecord/lib/active_record/relation/finder_methods.rb, line 149
def last(limit = nil)
  return find_last(limit) if loaded? || limit_value

  result = ordered_relation.limit(limit)
  result = result.reverse_order!

  limit ? result.reverse : result.first
end
last!() click to toggle source

Same as last but raises ActiveRecord::RecordNotFound if no record is found. Note that last! accepts no arguments.

# File activerecord/lib/active_record/relation/finder_methods.rb, line 160
def last!
  last || raise_record_not_found_exception!
end
second() click to toggle source

Find the second record. If no order is defined it will order by primary key.

Person.second # returns the second object fetched by SELECT * FROM people
Person.offset(3).second # returns the second object from OFFSET 3 (which is OFFSET 4)
Person.where(["user_name = :u", { u: user_name }]).second
# File activerecord/lib/active_record/relation/finder_methods.rb, line 170
def second
  find_nth 1
end
second!() click to toggle source

Same as second but raises ActiveRecord::RecordNotFound if no record is found.

# File activerecord/lib/active_record/relation/finder_methods.rb, line 176
def second!
  second || raise_record_not_found_exception!
end
second_to_last() click to toggle source

Find the second-to-last record. If no order is defined it will order by primary key.

Person.second_to_last # returns the second-to-last object fetched by SELECT * FROM people
Person.offset(3).second_to_last # returns the second-to-last object from OFFSET 3
Person.where(["user_name = :u", { u: user_name }]).second_to_last
# File activerecord/lib/active_record/relation/finder_methods.rb, line 266
def second_to_last
  find_nth_from_last 2
end
second_to_last!() click to toggle source

Same as second_to_last but raises ActiveRecord::RecordNotFound if no record is found.

# File activerecord/lib/active_record/relation/finder_methods.rb, line 272
def second_to_last!
  second_to_last || raise_record_not_found_exception!
end
take(limit = nil) click to toggle source

Gives a record (or N records if a parameter is supplied) without any implied order. The order will depend on the database implementation. If an order is supplied it will be respected.

Person.take # returns an object fetched by SELECT * FROM people LIMIT 1
Person.take(5) # returns 5 objects fetched by SELECT * FROM people LIMIT 5
Person.where(["name LIKE '%?'", name]).take
# File activerecord/lib/active_record/relation/finder_methods.rb, line 101
def take(limit = nil)
  limit ? find_take_with_limit(limit) : find_take
end
take!() click to toggle source

Same as take but raises ActiveRecord::RecordNotFound if no record is found. Note that take! accepts no arguments.

# File activerecord/lib/active_record/relation/finder_methods.rb, line 107
def take!
  take || raise_record_not_found_exception!
end
third() click to toggle source

Find the third record. If no order is defined it will order by primary key.

Person.third # returns the third object fetched by SELECT * FROM people
Person.offset(3).third # returns the third object from OFFSET 3 (which is OFFSET 5)
Person.where(["user_name = :u", { u: user_name }]).third
# File activerecord/lib/active_record/relation/finder_methods.rb, line 186
def third
  find_nth 2
end
third!() click to toggle source

Same as third but raises ActiveRecord::RecordNotFound if no record is found.

# File activerecord/lib/active_record/relation/finder_methods.rb, line 192
def third!
  third || raise_record_not_found_exception!
end
third_to_last() click to toggle source

Find the third-to-last record. If no order is defined it will order by primary key.

Person.third_to_last # returns the third-to-last object fetched by SELECT * FROM people
Person.offset(3).third_to_last # returns the third-to-last object from OFFSET 3
Person.where(["user_name = :u", { u: user_name }]).third_to_last
# File activerecord/lib/active_record/relation/finder_methods.rb, line 250
def third_to_last
  find_nth_from_last 3
end
third_to_last!() click to toggle source

Same as third_to_last but raises ActiveRecord::RecordNotFound if no record is found.

# File activerecord/lib/active_record/relation/finder_methods.rb, line 256
def third_to_last!
  third_to_last || raise_record_not_found_exception!
end

Private Instance Methods

apply_join_dependency(relation, join_dependency) click to toggle source
# File activerecord/lib/active_record/relation/finder_methods.rb, line 400
def apply_join_dependency(relation, join_dependency)
  relation = relation.except(:includes, :eager_load, :preload).joins!(join_dependency)

  if using_limitable_reflections?(join_dependency.reflections)
    relation
  else
    if relation.limit_value
      limited_ids = limited_ids_for(relation)
      limited_ids.empty? ? relation.none! : relation.where!(primary_key => limited_ids)
    end
    relation.except(:limit, :offset)
  end
end
construct_join_dependency(joins = [], eager_loading: true) click to toggle source
# File activerecord/lib/active_record/relation/finder_methods.rb, line 391
def construct_join_dependency(joins = [], eager_loading: true)
  including = eager_load_values + includes_values
  ActiveRecord::Associations::JoinDependency.new(klass, table, including, joins, eager_loading: eager_loading)
end
construct_relation_for_association_calculations() click to toggle source
# File activerecord/lib/active_record/relation/finder_methods.rb, line 396
def construct_relation_for_association_calculations
  apply_join_dependency(self, construct_join_dependency(joins_values))
end
construct_relation_for_exists(relation, conditions) click to toggle source
# File activerecord/lib/active_record/relation/finder_methods.rb, line 378
def construct_relation_for_exists(relation, conditions)
  relation = relation.except(:select, :distinct, :order)._select!(ONE_AS_ONE).limit!(1)

  case conditions
  when Array, Hash
    relation.where!(conditions)
  else
    relation.where!(primary_key => conditions) unless conditions == :none
  end

  relation
end
find_last(limit) click to toggle source
# File activerecord/lib/active_record/relation/finder_methods.rb, line 554
def find_last(limit)
  limit ? records.last(limit) : records.last
end
find_nth(index) click to toggle source
# File activerecord/lib/active_record/relation/finder_methods.rb, line 520
def find_nth(index)
  @offsets[offset_index + index] ||= find_nth_with_limit(index, 1).first
end
find_nth_from_last(index) click to toggle source
# File activerecord/lib/active_record/relation/finder_methods.rb, line 539
def find_nth_from_last(index)
  if loaded?
    records[-index]
  else
    relation = ordered_relation

    relation.to_a[-index]
    # TODO: can be made more performant on large result sets by
    # for instance, last(index)[-index] (which would require
    # refactoring the last(n) finder method to make test suite pass),
    # or by using a combination of reverse_order, limit, and offset,
    # e.g., reverse_order.offset(index-1).first
  end
end
find_nth_with_limit(index, limit) click to toggle source
# File activerecord/lib/active_record/relation/finder_methods.rb, line 524
def find_nth_with_limit(index, limit)
  if loaded?
    records[index, limit] || []
  else
    relation = ordered_relation

    if limit_value.nil? || index < limit_value
      relation = relation.offset(offset_index + index) unless index.zero?
      relation.limit(limit).to_a
    else
      []
    end
  end
end
find_one(id) click to toggle source
# File activerecord/lib/active_record/relation/finder_methods.rb, line 449
      def find_one(id)
        if ActiveRecord::Base === id
          raise ArgumentError, <<-MSG.squish
            You are passing an instance of ActiveRecord::Base to `find`.
            Please pass the id of the object by calling `.id`.
          MSG
        end

        relation = where(primary_key => id)
        record = relation.take

        raise_record_not_found_exception!(id, 0, 1) unless record

        record
      end
find_some(ids) click to toggle source
# File activerecord/lib/active_record/relation/finder_methods.rb, line 465
def find_some(ids)
  return find_some_ordered(ids) unless order_values.present?

  result = where(primary_key => ids).to_a

  expected_size =
    if limit_value && ids.size > limit_value
      limit_value
    else
      ids.size
    end

  # 11 ids with limit 3, offset 9 should give 2 results.
  if offset_value && (ids.size - offset_value < expected_size)
    expected_size = ids.size - offset_value
  end

  if result.size == expected_size
    result
  else
    raise_record_not_found_exception!(ids, result.size, expected_size)
  end
end
find_some_ordered(ids) click to toggle source
# File activerecord/lib/active_record/relation/finder_methods.rb, line 489
def find_some_ordered(ids)
  ids = ids.slice(offset_value || 0, limit_value || ids.size) || []

  result = except(:limit, :offset).where(primary_key => ids).records

  if result.size == ids.size
    pk_type = @klass.type_for_attribute(primary_key)

    records_by_id = result.index_by(&:id)
    ids.map { |id| records_by_id.fetch(pk_type.cast(id)) }
  else
    raise_record_not_found_exception!(ids, result.size, ids.size)
  end
end
find_take() click to toggle source
# File activerecord/lib/active_record/relation/finder_methods.rb, line 504
def find_take
  if loaded?
    records.first
  else
    @take ||= limit(1).records.first
  end
end
find_take_with_limit(limit) click to toggle source
# File activerecord/lib/active_record/relation/finder_methods.rb, line 512
def find_take_with_limit(limit)
  if loaded?
    records.take(limit)
  else
    limit(limit).to_a
  end
end
find_with_associations() { |relation, join_dependency| ... } click to toggle source
# File activerecord/lib/active_record/relation/finder_methods.rb, line 359
def find_with_associations
  # NOTE: the JoinDependency constructed here needs to know about
  #       any joins already present in `self`, so pass them in
  #
  # failing to do so means that in cases like activerecord/test/cases/associations/inner_join_association_test.rb:136
  # incorrect SQL is generated. In that case, the join dependency for
  # SpecialCategorizations is constructed without knowledge of the
  # preexisting join in joins_values to categorizations (by way of
  # the `has_many :through` for categories).
  #
  join_dependency = construct_join_dependency(joins_values)

  aliases  = join_dependency.aliases
  relation = select aliases.columns
  relation = apply_join_dependency(relation, join_dependency)

  yield relation, join_dependency
end
find_with_ids(*ids) click to toggle source
# File activerecord/lib/active_record/relation/finder_methods.rb, line 428
def find_with_ids(*ids)
  raise UnknownPrimaryKey.new(@klass) if primary_key.nil?

  expects_array = ids.first.kind_of?(Array)
  return ids.first if expects_array && ids.first.empty?

  ids = ids.flatten.compact.uniq

  case ids.size
  when 0
    raise RecordNotFound, "Couldn't find #{@klass.name} without an ID"
  when 1
    result = find_one(ids.first)
    expects_array ? [ result ] : result
  else
    find_some(ids)
  end
rescue ::RangeError
  raise RecordNotFound, "Couldn't find #{@klass.name} with an out of range ID"
end
limited_ids_for(relation) click to toggle source
# File activerecord/lib/active_record/relation/finder_methods.rb, line 414
def limited_ids_for(relation)
  values = @klass.connection.columns_for_distinct(
    "#{quoted_table_name}.#{quoted_primary_key}", relation.order_values)

  relation = relation.except(:select).select(values).distinct!

  id_rows = skip_query_cache_if_necessary { @klass.connection.select_all(relation.arel, "SQL") }
  id_rows.map { |row| row[primary_key] }
end
offset_index() click to toggle source
# File activerecord/lib/active_record/relation/finder_methods.rb, line 355
def offset_index
  offset_value || 0
end
ordered_relation() click to toggle source
# File activerecord/lib/active_record/relation/finder_methods.rb, line 558
def ordered_relation
  if order_values.empty? && primary_key
    order(arel_attribute(primary_key).asc)
  else
    self
  end
end
using_limitable_reflections?(reflections) click to toggle source
# File activerecord/lib/active_record/relation/finder_methods.rb, line 424
def using_limitable_reflections?(reflections)
  reflections.none?(&:collection?)
end