module ActiveRecord::FinderMethods

Constants

ONE_AS_ONE

Public Instance Methods

exists?(conditions = :none) Show source

# File activerecord/lib/active_record/relation/finder_methods.rb, line 310
    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`.
".squish)
      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 = relation.where(primary_key => conditions)
        end
      end

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

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?

fifth() Show source

# File activerecord/lib/active_record/relation/finder_methods.rb, line 225
def fifth
  find_nth 4
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

fifth!() Show source

# File activerecord/lib/active_record/relation/finder_methods.rb, line 231
def fifth!
  find_nth! 4
end

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

find(*args) Show source

# File activerecord/lib/active_record/relation/finder_methods.rb, line 64
def find(*args)
  return super if block_given?
  find_with_ids(*args)
end

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 ActiveRecord::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

find_by(arg, *args) Show source

# File activerecord/lib/active_record/relation/finder_methods.rb, line 77
def find_by(arg, *args)
  where(arg, *args).take
rescue RangeError
  nil
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

find_by!(arg, *args) Show source

# File activerecord/lib/active_record/relation/finder_methods.rb, line 85
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

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

first(limit = nil) Show source

# File activerecord/lib/active_record/relation/finder_methods.rb, line 118
def first(limit = nil)
  if limit
    find_nth_with_limit_and_offset(0, limit, offset: offset_index)
  else
    find_nth 0
  end
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

first!() Show source

# File activerecord/lib/active_record/relation/finder_methods.rb, line 128
def first!
  find_nth! 0
end

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

forty_two() Show source

# File activerecord/lib/active_record/relation/finder_methods.rb, line 241
def forty_two
  find_nth 41
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

forty_two!() Show source

# File activerecord/lib/active_record/relation/finder_methods.rb, line 247
def forty_two!
  find_nth! 41
end

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

fourth() Show source

# File activerecord/lib/active_record/relation/finder_methods.rb, line 209
def fourth
  find_nth 3
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

fourth!() Show source

# File activerecord/lib/active_record/relation/finder_methods.rb, line 215
def fourth!
  find_nth! 3
end

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

last(limit = nil) Show source

# File activerecord/lib/active_record/relation/finder_methods.rb, line 147
    def last(limit = nil)
      return find_last(limit) if loaded? || limit_value

      result = limit(limit || 1)
      result.order!(arel_attribute(primary_key)) if order_values.empty? && primary_key
      result = result.reverse_order!

      limit ? result.reverse : result.first
    rescue ActiveRecord::IrreversibleOrderError
      ActiveSupport::Deprecation.warn("          Finding a last element by loading the relation when SQL ORDER
          can not be reversed is deprecated.
          Rails 5.1 will raise ActiveRecord::IrreversibleOrderError in this case.
          Please call `to_a.last` if you still want to load the relation.
".squish)
      find_last(limit)
    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>]

last!() Show source

# File activerecord/lib/active_record/relation/finder_methods.rb, line 167
def last!
  last or raise RecordNotFound.new("Couldn't find #{@klass.name} with [#{arel.where_sql(@klass.arel_engine)}]")
end

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

second() Show source

# File activerecord/lib/active_record/relation/finder_methods.rb, line 177
def second
  find_nth 1
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

second!() Show source

# File activerecord/lib/active_record/relation/finder_methods.rb, line 183
def second!
  find_nth! 1
end

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

second_to_last() Show source

# File activerecord/lib/active_record/relation/finder_methods.rb, line 273
def second_to_last
  find_nth_from_last 2
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

second_to_last!() Show source

# File activerecord/lib/active_record/relation/finder_methods.rb, line 279
def second_to_last!
  find_nth_from_last 2 or raise RecordNotFound.new("Couldn't find #{@klass.name} with [#{arel.where_sql(@klass.arel_engine)}]")
end

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

take(limit = nil) Show source

# File activerecord/lib/active_record/relation/finder_methods.rb, line 99
def take(limit = nil)
  limit ? limit(limit).to_a : find_take
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

take!() Show source

# File activerecord/lib/active_record/relation/finder_methods.rb, line 105
def take!
  take or raise RecordNotFound.new("Couldn't find #{@klass.name} with [#{arel.where_sql(@klass.arel_engine)}]")
end

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

third() Show source

# File activerecord/lib/active_record/relation/finder_methods.rb, line 193
def third
  find_nth 2
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

third!() Show source

# File activerecord/lib/active_record/relation/finder_methods.rb, line 199
def third!
  find_nth! 2
end

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

third_to_last() Show source

# File activerecord/lib/active_record/relation/finder_methods.rb, line 257
def third_to_last
  find_nth_from_last 3
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

third_to_last!() Show source

# File activerecord/lib/active_record/relation/finder_methods.rb, line 263
def third_to_last!
  find_nth_from_last 3 or raise RecordNotFound.new("Couldn't find #{@klass.name} with [#{arel.where_sql(@klass.arel_engine)}]")
end

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

Protected Instance Methods

find_nth(index, offset = nil) Show source

# File activerecord/lib/active_record/relation/finder_methods.rb, line 531
    def find_nth(index, offset = nil)
      # TODO: once the offset argument is removed we rely on offset_index
      # within find_nth_with_limit, rather than pass it in via
      # find_nth_with_limit_and_offset
      if offset
        ActiveSupport::Deprecation.warn("          Passing an offset argument to find_nth is deprecated,
          please use Relation#offset instead.
".squish)
      end
      if loaded?
        records[index]
      else
        offset ||= offset_index
        @offsets[offset + index] ||= find_nth_with_limit_and_offset(index, 1, offset: offset).first
      end
    end

find_nth!(index) Show source

# File activerecord/lib/active_record/relation/finder_methods.rb, line 549
def find_nth!(index)
  find_nth(index) or raise RecordNotFound.new("Couldn't find #{@klass.name} with [#{arel.where_sql(@klass.arel_engine)}]")
end

find_nth_from_last(index) Show source

# File activerecord/lib/active_record/relation/finder_methods.rb, line 566
def find_nth_from_last(index)
  if loaded?
    records[-index]
  else
    relation = if order_values.empty? && primary_key
                 order(arel_attribute(primary_key).asc)
               else
                 self
               end

    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) Show source

# File activerecord/lib/active_record/relation/finder_methods.rb, line 553
def find_nth_with_limit(index, limit)
  # TODO: once the offset argument is removed from find_nth,
  # find_nth_with_limit_and_offset can be merged into this method
  relation = if order_values.empty? && primary_key
               order(arel_attribute(primary_key).asc)
             else
               self
             end

  relation = relation.offset(index) unless index.zero?
  relation.limit(limit).to_a
end

find_one(id) Show source

# File activerecord/lib/active_record/relation/finder_methods.rb, line 467
    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`.
".squish)
      end

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

      raise_record_not_found_exception!(id, 0, 1) unless record

      record
    end

find_some(ids) Show source

# File activerecord/lib/active_record/relation/finder_methods.rb, line 484
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) Show source

# File activerecord/lib/active_record/relation/finder_methods.rb, line 508
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() Show source

# File activerecord/lib/active_record/relation/finder_methods.rb, line 523
def find_take
  if loaded?
    records.first
  else
    @take ||= limit(1).records.first
  end
end

find_with_ids(*ids) Show source

# File activerecord/lib/active_record/relation/finder_methods.rb, line 446
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