Methods
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F
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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 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 305
    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

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

      relation = construct_relation_for_exists(conditions)

      skip_query_cache_if_necessary { connection.select_one(relation.arel, "#{name} Exists") } ? true : false
    rescue ::RangeError
      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 219
def fifth
  find_nth 4
end
fifth!()

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

# File activerecord/lib/active_record/relation/finder_methods.rb, line 225
def fifth!
  fifth || raise_record_not_found_exception!
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 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 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.
# File activerecord/lib/active_record/relation/finder_methods.rb, line 67
def find(*args)
  return super if block_given?
  find_with_ids(*args)
end
find_by(arg, *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 80
def find_by(arg, *args)
  where(arg, *args).take
rescue ::RangeError
  nil
end
find_by!(arg, *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!(arg, *args)
  where(arg, *args).take!
rescue ::RangeError
  raise RecordNotFound.new("Couldn't find #{@klass.name} with an out of range value",
                           @klass.name, @klass.primary_key)
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 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 121
def first(limit = nil)
  if limit
    find_nth_with_limit(0, limit)
  else
    find_nth 0
  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 131
def first!
  first || raise_record_not_found_exception!
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 235
def forty_two
  find_nth 41
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 241
def forty_two!
  forty_two || raise_record_not_found_exception!
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 203
def fourth
  find_nth 3
end
fourth!()

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

# File activerecord/lib/active_record/relation/finder_methods.rb, line 209
def fourth!
  fourth || raise_record_not_found_exception!
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 150
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
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 161
def last!
  last || raise_record_not_found_exception!
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 171
def second
  find_nth 1
end
second!()

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

# File activerecord/lib/active_record/relation/finder_methods.rb, line 177
def second!
  second || raise_record_not_found_exception!
end
second_to_last()

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 267
def second_to_last
  find_nth_from_last 2
end
second_to_last!()

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

# File activerecord/lib/active_record/relation/finder_methods.rb, line 273
def second_to_last!
  second_to_last || raise_record_not_found_exception!
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 102
def take(limit = nil)
  limit ? find_take_with_limit(limit) : 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 108
def take!
  take || raise_record_not_found_exception!
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 187
def third
  find_nth 2
end
third!()

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

# File activerecord/lib/active_record/relation/finder_methods.rb, line 193
def third!
  third || raise_record_not_found_exception!
end
third_to_last()

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 251
def third_to_last
  find_nth_from_last 3
end
third_to_last!()

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

# File activerecord/lib/active_record/relation/finder_methods.rb, line 257
def third_to_last!
  third_to_last || raise_record_not_found_exception!
end