# module ActiveRecord::FinderMethods

### Constants

ONE_AS_ONE

### Public Instance Methods

exists?(conditions = :none) click to toggle source

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 lib/active_record/relation/finder_methods.rb, line 302
        def exists?(conditions = :none)
          if Base === conditions
            raise ArgumentError, "          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 || limit_value == 0

          relation = self unless eager_loading?
          relation ||= apply_join_dependency(self, construct_join_dependency(eager_loading: false))

          return false if ActiveRecord::NullRelation === relation

          relation = construct_relation_for_exists(relation, conditions)

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

fifth() click to toggle source

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 lib/active_record/relation/finder_methods.rb, line 217
    def fifth
      find_nth 4
    end

fifth!() click to toggle source

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

    # File lib/active_record/relation/finder_methods.rb, line 223
    def fifth!
      fifth || raise_record_not_found_exception!
    end

find(*args) click to toggle source

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

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

find_by(arg, *args) click to toggle source

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

find_by!(arg, *args) click to toggle source

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

    # File 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

first(limit = nil) click to toggle source

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 lib/active_record/relation/finder_methods.rb, line 118
    def first(limit = nil)
      if limit
        find_nth_with_limit(0, limit)
      else
        find_nth 0
      end
    end

first!() click to toggle source

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

    # File lib/active_record/relation/finder_methods.rb, line 128
    def first!
      first || raise_record_not_found_exception!
    end

forty_two() click to toggle source

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 lib/active_record/relation/finder_methods.rb, line 233
    def forty_two
      find_nth 41
    end

forty_two!() click to toggle source

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

    # File lib/active_record/relation/finder_methods.rb, line 239
    def forty_two!
      forty_two || raise_record_not_found_exception!
    end

fourth() click to toggle source

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 lib/active_record/relation/finder_methods.rb, line 201
    def fourth
      find_nth 3
    end

fourth!() click to toggle source

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

    # File lib/active_record/relation/finder_methods.rb, line 207
    def fourth!
      fourth || raise_record_not_found_exception!
    end

last(limit = nil) click to toggle source

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

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

      limit ? result.reverse : result.first
    end

last!() click to toggle source

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

    # File lib/active_record/relation/finder_methods.rb, line 159
    def last!
      last || raise_record_not_found_exception!
    end

second() click to toggle source

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 lib/active_record/relation/finder_methods.rb, line 169
    def second
      find_nth 1
    end

second!() click to toggle source

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

    # File lib/active_record/relation/finder_methods.rb, line 175
    def second!
      second || raise_record_not_found_exception!
    end

second_to_last() click to toggle source

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 lib/active_record/relation/finder_methods.rb, line 265
    def second_to_last
      find_nth_from_last 2
    end

second_to_last!() click to toggle source

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

    # File lib/active_record/relation/finder_methods.rb, line 271
    def second_to_last!
      second_to_last || raise_record_not_found_exception!
    end

take(limit = nil) click to toggle source

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 lib/active_record/relation/finder_methods.rb, line 99
    def take(limit = nil)
      limit ? find_take_with_limit(limit) : find_take
    end

take!() click to toggle source

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

    # File lib/active_record/relation/finder_methods.rb, line 105
    def take!
      take || raise_record_not_found_exception!
    end

third() click to toggle source

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 lib/active_record/relation/finder_methods.rb, line 185
    def third
      find_nth 2
    end

third!() click to toggle source

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

    # File lib/active_record/relation/finder_methods.rb, line 191
    def third!
      third || raise_record_not_found_exception!
    end

third_to_last() click to toggle source

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 lib/active_record/relation/finder_methods.rb, line 249
    def third_to_last
      find_nth_from_last 3
    end

third_to_last!() click to toggle source

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

    # File lib/active_record/relation/finder_methods.rb, line 255
    def third_to_last!
      third_to_last || raise_record_not_found_exception!
    end

### Private Instance Methods

apply_join_dependency(relation, join_dependency) click to toggle source

    # File lib/active_record/relation/finder_methods.rb, line 409
    def apply_join_dependency(relation, join_dependency)
      relation = relation.except(:includes, :eager_load, :preload).joins!(join_dependency)

      if using_limitable_reflections?(join_dependency.reflections)
        relation
      else
        if relation.limit_value
          limited_ids = limited_ids_for(relation)
          limited_ids.empty? ? relation.none! : relation.where!(primary_key => limited_ids)
        end
        relation.except(:limit, :offset)
      end
    end

construct_join_dependency(joins = [], eager_loading: true) click to toggle source

    # File lib/active_record/relation/finder_methods.rb, line 400
    def construct_join_dependency(joins = [], eager_loading: true)
      including = eager_load_values + includes_values
      ActiveRecord::Associations::JoinDependency.new(@klass, including, joins, eager_loading: eager_loading)
    end

construct_relation_for_association_calculations() click to toggle source

    # File lib/active_record/relation/finder_methods.rb, line 405
    def construct_relation_for_association_calculations
      apply_join_dependency(self, construct_join_dependency(joins_values))
    end

construct_relation_for_exists(relation, conditions) click to toggle source

    # File lib/active_record/relation/finder_methods.rb, line 387
    def construct_relation_for_exists(relation, conditions)
      relation = relation.except(:select, :distinct, :order)._select!(ONE_AS_ONE).limit!(1)

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

      relation
    end

find_last(limit) click to toggle source

    # File lib/active_record/relation/finder_methods.rb, line 572
    def find_last(limit)
      limit ? records.last(limit) : records.last
    end

find_nth(index) click to toggle source

    # File lib/active_record/relation/finder_methods.rb, line 530
    def find_nth(index)
      @offsets[offset_index + index] ||= find_nth_with_limit(index, 1).first
    end

find_nth_from_last(index) click to toggle source

    # File lib/active_record/relation/finder_methods.rb, line 553
    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) click to toggle source

    # File lib/active_record/relation/finder_methods.rb, line 534
    def find_nth_with_limit(index, limit)
      if loaded?
        records[index, limit] || []
      else
        relation = if order_values.empty? && primary_key
          order(arel_attribute(primary_key).asc)
        else
          self
        end

        if limit_value.nil? || index < limit_value
          relation = relation.offset(offset_index + index) unless index.zero?
          relation.limit(limit).to_a
        else
          []
        end
      end
    end

find_one(id) click to toggle source

    # File lib/active_record/relation/finder_methods.rb, line 459
          def find_one(id)
            if ActiveRecord::Base === id
              raise ArgumentError, "            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) click to toggle source

    # File lib/active_record/relation/finder_methods.rb, line 475
    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) click to toggle source

    # File lib/active_record/relation/finder_methods.rb, line 499
    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() click to toggle source

    # File lib/active_record/relation/finder_methods.rb, line 514
    def find_take
      if loaded?
        records.first
      else
        @take ||= limit(1).records.first
      end
    end

find_take_with_limit(limit) click to toggle source

    # File lib/active_record/relation/finder_methods.rb, line 522
    def find_take_with_limit(limit)
      if loaded?
        records.take(limit)
      else
        limit(limit).to_a
      end
    end

find_with_associations() { |relation| ... } click to toggle source

    # File lib/active_record/relation/finder_methods.rb, line 358
    def find_with_associations
      # NOTE: the JoinDependency constructed here needs to know about
      #       any joins already present in `self`, so pass them in
      #
      # failing to do so means that in cases like activerecord/test/cases/associations/inner_join_association_test.rb:136
      # incorrect SQL is generated. In that case, the join dependency for
      # SpecialCategorizations is constructed without knowledge of the
      # preexisting join in joins_values to categorizations (by way of
      # the `has_many :through` for categories).
      #
      join_dependency = construct_join_dependency(joins_values)

      aliases  = join_dependency.aliases
      relation = select aliases.columns
      relation = apply_join_dependency(relation, join_dependency)

      if block_given?
        yield relation
      else
        if ActiveRecord::NullRelation === relation
          []
        else
          arel = relation.arel
          rows = connection.select_all(arel, "SQL", relation.bound_attributes)
          join_dependency.instantiate(rows, aliases)
        end
      end
    end

find_with_ids(*ids) click to toggle source

    # File lib/active_record/relation/finder_methods.rb, line 438
    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

limited_ids_for(relation) click to toggle source

    # File lib/active_record/relation/finder_methods.rb, line 423
    def limited_ids_for(relation)
      values = @klass.connection.columns_for_distinct(
        "#{quoted_table_name}.#{quoted_primary_key}", relation.order_values)

      relation = relation.except(:select).select(values).distinct!
      arel = relation.arel

      id_rows = @klass.connection.select_all(arel, "SQL", relation.bound_attributes)
      id_rows.map { |row| row[primary_key] }
    end

offset_index() click to toggle source

    # File lib/active_record/relation/finder_methods.rb, line 354
    def offset_index
      offset_value || 0
    end

using_limitable_reflections?(reflections) click to toggle source

    # File lib/active_record/relation/finder_methods.rb, line 434
    def using_limitable_reflections?(reflections)
      reflections.none?(&:collection?)
    end