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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 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 300
    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
    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 214
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 220
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 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)
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
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 86
def find_by!(arg, *args)
  where(arg, *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 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 116
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 126
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 230
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 236
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 198
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 204
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 145
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 156
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 166
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 172
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 262
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 268
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 97
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 103
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 182
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 188
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 246
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 252
def third_to_last!
  third_to_last || raise_record_not_found_exception!
end