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Methods
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Constants
ONE_AS_ONE = '1 AS one'
 
Instance Public methods
exists?(conditions = :none)

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 284
def exists?(conditions = :none)
  if Base === conditions
    conditions = conditions.id
    ActiveSupport::Deprecation.warn "You are passing an instance of ActiveRecord::Base to `exists?`."            "Please pass the id of the object by calling `.id`"
  end

  return false if !conditions

  relation = apply_join_dependency(self, construct_join_dependency)
  return false if ActiveRecord::NullRelation === relation

  relation = relation.except(:select, :order).select(ONE_AS_ONE).limit(1)

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

  connection.select_value(relation, "#{name} Exists", relation.bind_values) ? true : false
end
fifth()

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 231
def fifth
  find_nth(4, offset_index)
end
fifth!()

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

# File activerecord/lib/active_record/relation/finder_methods.rb, line 237
def fifth!
  fifth or raise RecordNotFound
end
find(*args)

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 no record can be found for all of the listed 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)

ActiveRecord::RecordNotFound will be raised if one or more ids are not found.

NOTE: The returned records may not be in the same order as the ids you provide since database rows are unordered. You'd need to provide an explicit order option if you want the results are 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.where(name: 'Spartacus', rating: 4).first_or_initialize
# returns the first item or returns a new instance (requires you call .save to persist against the database).

Person.where(name: 'Spartacus', rating: 4).first_or_create
# returns the first item or creates it and returns it, available since Rails 3.2.1.

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, available since Rails 3.2.1.

Person.where(name: 'Spartacus', rating: 4).pluck(:field1, :field2)
# returns an Array of the required fields, available since Rails 3.1.
# File activerecord/lib/active_record/relation/finder_methods.rb, line 66
def find(*args)
  if block_given?
    to_a.find(*args) { |*block_args| yield(*block_args) }
  else
    find_with_ids(*args)
  end
end
find_by(*args)

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 82
def find_by(*args)
  where(*args).take
end
find_by!(*args)

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 88
def find_by!(*args)
  where(*args).take!
end
first(limit = nil)

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
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 LIMIT 3

Rails 3

Person.first # SELECT "people".* FROM "people" LIMIT 1

NOTE: Rails 3 may not order this query by the primary key and the order will depend on the database implementation. In order to ensure that behavior, use User.order(:id).first instead.

Rails 4

Person.first # SELECT "people".* FROM "people" ORDER BY "people"."id" ASC LIMIT 1
# File activerecord/lib/active_record/relation/finder_methods.rb, line 130
def first(limit = nil)
  if limit
    find_nth_with_limit(offset_index, limit)
  else
    find_nth(0, offset_index)
  end
end
first!()

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 140
def first!
  first or raise RecordNotFound
end
forty_two()

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 247
def forty_two
  find_nth(41, offset_index)
end
forty_two!()

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

# File activerecord/lib/active_record/relation/finder_methods.rb, line 253
def forty_two!
  forty_two or raise RecordNotFound
end
fourth()

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 215
def fourth
  find_nth(3, offset_index)
end
fourth!()

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

# File activerecord/lib/active_record/relation/finder_methods.rb, line 221
def fourth!
  fourth or raise RecordNotFound
end
last(limit = nil)

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 159
def last(limit = nil)
  if limit
    if order_values.empty? && primary_key
      order(arel_table[primary_key].desc).limit(limit).reverse
    else
      to_a.last(limit)
    end
  else
    find_last
  end
end
last!()

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 173
def last!
  last or raise RecordNotFound
end
second()

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 183
def second
  find_nth(1, offset_index)
end
second!()

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

# File activerecord/lib/active_record/relation/finder_methods.rb, line 189
def second!
  second or raise RecordNotFound
end
take(limit = nil)

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 99
def take(limit = nil)
  limit ? limit(limit).to_a : find_take
end
take!()

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 105
def take!
  take or raise RecordNotFound
end
third()

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 199
def third
  find_nth(2, offset_index)
end
third!()

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

# File activerecord/lib/active_record/relation/finder_methods.rb, line 205
def third!
  third or raise RecordNotFound
end
Instance Protected methods
find_last()
# File activerecord/lib/active_record/relation/finder_methods.rb, line 502
def find_last
  if loaded?
    @records.last
  else
    @last ||=
      if limit_value
        to_a.last
      else
        reverse_order.limit(1).to_a.first
      end
  end
end
find_nth(index, offset)
# File activerecord/lib/active_record/relation/finder_methods.rb, line 482
def find_nth(index, offset)
  if loaded?
    @records[index]
  else
    offset += index
    @offsets[offset] ||= find_nth_with_limit(offset, 1).first
  end
end
find_nth_with_limit(offset, limit)
# File activerecord/lib/active_record/relation/finder_methods.rb, line 491
def find_nth_with_limit(offset, limit)
  relation = if order_values.empty? && primary_key
               order(arel_table[primary_key].asc)
             else
               self
             end

  relation = relation.offset(offset) unless offset.zero?
  relation.limit(limit).to_a
end
find_one(id)
# File activerecord/lib/active_record/relation/finder_methods.rb, line 434
def find_one(id)
  if ActiveRecord::Base === id
    id = id.id
    ActiveSupport::Deprecation.warn "You are passing an instance of ActiveRecord::Base to `find`."            "Please pass the id of the object by calling `.id`"
  end

  column = columns_hash[primary_key]
  substitute = connection.substitute_at(column, bind_values.length)
  relation = where(table[primary_key].eq(substitute))
  relation.bind_values += [[column, id]]
  record = relation.take

  raise_record_not_found_exception!(id, 0, 1) unless record

  record
end
find_some(ids)
# File activerecord/lib/active_record/relation/finder_methods.rb, line 452
def find_some(ids)
  result = where(table[primary_key].in(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_take()
# File activerecord/lib/active_record/relation/finder_methods.rb, line 474
def find_take
  if loaded?
    @records.first
  else
    @take ||= limit(1).to_a.first
  end
end
find_with_ids(*ids)
# File activerecord/lib/active_record/relation/finder_methods.rb, line 415
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
end