module ActiveRecord::FinderMethods

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 where-style conditions (such as ['name LIKE ?', "%#{query}%"]).

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

• false - Returns always false.

• No args - Returns false if the relation 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?
Person.where(name: 'Spartacus', rating: 4).exists?

# File activerecord/lib/active_record/relation/finder_methods.rb, line 357
    def exists?(conditions = :none)
      return false if @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

      if eager_loading?
        relation = apply_join_dependency(eager_loading: false)
        return relation.exists?(conditions)
      end

      relation = construct_relation_for_exists(conditions)
      return false if relation.where_clause.contradiction?

      skip_query_cache_if_necessary do
        with_connection do |c|
          c.select_rows(relation.arel, "#{name} Exists?").size == 1
        end
      end
    end

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 271
def fifth
  find_nth 4
end

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

# File activerecord/lib/active_record/relation/finder_methods.rb, line 277
def fifth!
  fifth || raise_record_not_found_exception!
end

Find by id - This can either be a specific id (ID), a list of ids (ID, ID, ID), or an array of ids ([ID, ID, ID]). ‘ID` refers to an “identifier”. For models with a single-column primary key, `ID` will be a single value, and for models with a composite primary key, it will be an array of values. If one or more records cannot be found for the requested ids, then ActiveRecord::RecordNotFound will be raised. If the primary key is an integer, find by id coerces its arguments by 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), or with composite primary key [7, 17]
Person.find([1])        # returns an array for the object with ID = 1
Person.where("administrator = 1").order("created_on DESC").find(1)

Find a record for a composite primary key model¶ ↑

TravelRoute.primary_key = [:origin, :destination]

TravelRoute.find(["Ottawa", "London"])
=> #<TravelRoute origin: "Ottawa", destination: "London">

TravelRoute.find([["Paris", "Montreal"]])
=> [#<TravelRoute origin: "Paris", destination: "Montreal">]

TravelRoute.find(["New York", "Las Vegas"], ["New York", "Portland"])
=> [
     #<TravelRoute origin: "New York", destination: "Las Vegas">,
     #<TravelRoute origin: "New York", destination: "Portland">
   ]

TravelRoute.find([["Berlin", "London"], ["Barcelona", "Lisbon"]])
=> [
     #<TravelRoute origin: "Berlin", destination: "London">,
     #<TravelRoute origin: "Barcelona", destination: "Lisbon">
   ]

NOTE: The returned records are in the same order as the ids you provide. If you want the results to be sorted by database, you can use ActiveRecord::QueryMethods#where method and provide an explicit ActiveRecord::QueryMethods#order option. But ActiveRecord::QueryMethods#where method doesn’t raise ActiveRecord::RecordNotFound.

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.

Edge Cases¶ ↑

Person.find(37)          # raises ActiveRecord::RecordNotFound exception if the record with the given ID does not exist.
Person.find([37])        # raises ActiveRecord::RecordNotFound exception if the record with the given ID in the input array does not exist.
Person.find(nil)         # raises ActiveRecord::RecordNotFound exception if the argument is nil.
Person.find([])          # returns an empty array if the argument is an empty array.
Person.find              # raises ActiveRecord::RecordNotFound exception if the argument is not provided.

# File activerecord/lib/active_record/relation/finder_methods.rb, line 98
def find(*args)
  return super if block_given?
  find_with_ids(*args)
end

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 111
def find_by(arg, *args)
  where(arg, *args).take
end

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 117
def find_by!(arg, *args)
  where(arg, *args).take!
end

Finds the sole matching record. Raises ActiveRecord::RecordNotFound if no record is found. Raises ActiveRecord::SoleRecordExceeded if more than one record is found.

Product.find_sole_by(["price = %?", price])

# File activerecord/lib/active_record/relation/finder_methods.rb, line 160
def find_sole_by(arg, *args)
  where(arg, *args).sole
end

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 173
def first(limit = nil)
  if limit
    find_nth_with_limit(0, limit)
  else
    find_nth 0
  end
end

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 183
def first!
  first || raise_record_not_found_exception!
end

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 287
def forty_two
  find_nth 41
end

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

# File activerecord/lib/active_record/relation/finder_methods.rb, line 293
def forty_two!
  forty_two || raise_record_not_found_exception!
end

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 255
def fourth
  find_nth 3
end

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

# File activerecord/lib/active_record/relation/finder_methods.rb, line 261
def fourth!
  fourth || raise_record_not_found_exception!
end

Returns true if the relation contains the given record or false otherwise.

No query is performed if the relation is loaded; the given record is compared to the records in memory. If the relation is unloaded, an efficient existence query is performed, as in exists?.

# File activerecord/lib/active_record/relation/finder_methods.rb, line 389
def include?(record)
  # The existing implementation relies on receiving an Active Record instance as the input parameter named record.
  # Any non-Active Record object passed to this implementation is guaranteed to return `false`.
  return false unless record.is_a?(klass)

  if loaded? || offset_value || limit_value || having_clause.any?
    records.include?(record)
  else
    id = if record.class.composite_primary_key?
      record.class.primary_key.zip(record.id).to_h
    else
      record.id
    end

    exists?(id)
  end
end

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 202
def last(limit = nil)
  return find_last(limit) if loaded? || has_limit_or_offset?

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

  limit ? result.reverse : result.first
end

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 213
def last!
  last || raise_record_not_found_exception!
end

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 223
def second
  find_nth 1
end

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

# File activerecord/lib/active_record/relation/finder_methods.rb, line 229
def second!
  second || raise_record_not_found_exception!
end

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 319
def second_to_last
  find_nth_from_last 2
end

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

# File activerecord/lib/active_record/relation/finder_methods.rb, line 325
def second_to_last!
  second_to_last || raise_record_not_found_exception!
end

Finds the sole matching record. Raises ActiveRecord::RecordNotFound if no record is found. Raises ActiveRecord::SoleRecordExceeded if more than one record is found.

Product.where(["price = %?", price]).sole

# File activerecord/lib/active_record/relation/finder_methods.rb, line 143
def sole
  found, undesired = first(2)

  if found.nil?
    raise_record_not_found_exception!
  elsif undesired.present?
    raise ActiveRecord::SoleRecordExceeded.new(self)
  else
    found
  end
end

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 128
def take(limit = nil)
  limit ? find_take_with_limit(limit) : find_take
end

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 134
def take!
  take || raise_record_not_found_exception!
end

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 239
def third
  find_nth 2
end

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

# File activerecord/lib/active_record/relation/finder_methods.rb, line 245
def third!
  third || raise_record_not_found_exception!
end

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 303
def third_to_last
  find_nth_from_last 3
end

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

# File activerecord/lib/active_record/relation/finder_methods.rb, line 309
def third_to_last!
  third_to_last || raise_record_not_found_exception!
end