Methods
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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 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?(name: 'David')
Person.exists?(false)
Person.exists?

Source: show | on GitHub 

# File activerecord/lib/active_record/relation/finder_methods.rb, line 160
def exists?(conditions = :none)
  conditions = conditions.id if Base === conditions
  return false if !conditions

  join_dependency = construct_join_dependency_for_association_find
  relation = construct_relation_for_association_find(join_dependency)
  relation = relation.except(:select, :order).select("1 AS one").limit(1)

  case conditions
  when Array, Hash
    relation = relation.where(conditions)
  else
    relation = relation.where(table[primary_key].eq(conditions)) if conditions != :none
  end

  connection.select_value(relation, "#{name} Exists", relation.bind_values) ? true : false
rescue ThrowResult
  false
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 no record can be found for all of the listed 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 that returned records may not be in the same order as the ids you provide since database rows are unordered. Give an explicit order to ensure the results are 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

Source: show | on GitHub 

# File activerecord/lib/active_record/relation/finder_methods.rb, line 32
def find(*args)
  if block_given?
    to_a.find(*args) { |*block_args| yield(*block_args) }
  else
    find_with_ids(*args)
  end
end
find_by(*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

Source: show | on GitHub 

# File activerecord/lib/active_record/relation/finder_methods.rb, line 48
def find_by(*args)
  where(*args).take
end
find_by!(*args)

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

Source: show | on GitHub 

# File activerecord/lib/active_record/relation/finder_methods.rb, line 54
def find_by!(*args)
  where(*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
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 LIMIT 3

Source: show | on GitHub 

# File activerecord/lib/active_record/relation/finder_methods.rb, line 83
def first(limit = nil)
  if limit
    if order_values.empty? && primary_key
      order(arel_table[primary_key].asc).limit(limit).to_a
    else
      limit(limit).to_a
    end
  else
    find_first
  end
end
first!()

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

Source: show | on GitHub 

# File activerecord/lib/active_record/relation/finder_methods.rb, line 97
def first!
  first or raise RecordNotFound
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>]

Source: show | on GitHub 

# File activerecord/lib/active_record/relation/finder_methods.rb, line 116
def last(limit = nil)
  if limit
    if order_values.empty? && primary_key
      order(arel_table[primary_key].desc).limit(limit).reverse
    else
      to_a.last(limit)
    end
  else
    find_last
  end
end
last!()

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

Source: show | on GitHub 

# File activerecord/lib/active_record/relation/finder_methods.rb, line 130
def last!
  last or raise RecordNotFound
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

Source: show | on GitHub 

# File activerecord/lib/active_record/relation/finder_methods.rb, line 65
def take(limit = nil)
  limit ? limit(limit).to_a : find_take
end
take!()

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

Source: show | on GitHub 

# File activerecord/lib/active_record/relation/finder_methods.rb, line 71
def take!
  take or raise RecordNotFound
end
Instance Protected methods
apply_join_dependency(relation, join_dependency)

Source: show | on GitHub 

# File activerecord/lib/active_record/relation/finder_methods.rb, line 230
def apply_join_dependency(relation, join_dependency)
  join_dependency.join_associations.each do |association|
    relation = association.join_relation(relation)
  end

  limitable_reflections = using_limitable_reflections?(join_dependency.reflections)

  if !limitable_reflections && relation.limit_value
    limited_id_condition = construct_limited_ids_condition(relation.except(:select))
    relation = relation.where(limited_id_condition)
  end

  relation = relation.except(:limit, :offset) unless limitable_reflections

  relation
end
construct_join_dependency_for_association_find()

Source: show | on GitHub 

# File activerecord/lib/active_record/relation/finder_methods.rb, line 213
def construct_join_dependency_for_association_find
  including = (eager_load_values + includes_values).uniq
  ActiveRecord::Associations::JoinDependency.new(@klass, including, joins_values)
end
construct_limited_ids_condition(relation)

Source: show | on GitHub 

# File activerecord/lib/active_record/relation/finder_methods.rb, line 247
def construct_limited_ids_condition(relation)
  orders = relation.order_values.map { |val| val.presence }.compact
  values = @klass.connection.columns_for_distinct("#{quoted_table_name}.#{quoted_primary_key}", orders)

  relation = relation.dup.select(values).distinct!

  id_rows = @klass.connection.select_all(relation.arel, 'SQL', relation.bind_values)
  ids_array = id_rows.map {|row| row[primary_key]}

  ids_array.empty? ? raise(ThrowResult) : table[primary_key].in(ids_array)
end
construct_relation_for_association_calculations()

Source: show | on GitHub 

# File activerecord/lib/active_record/relation/finder_methods.rb, line 218
def construct_relation_for_association_calculations
  including = (eager_load_values + includes_values).uniq
  join_dependency = ActiveRecord::Associations::JoinDependency.new(@klass, including, arel.froms.first)
  relation = except(:includes, :eager_load, :preload)
  apply_join_dependency(relation, join_dependency)
end
construct_relation_for_association_find(join_dependency)

Source: show | on GitHub 

# File activerecord/lib/active_record/relation/finder_methods.rb, line 225
def construct_relation_for_association_find(join_dependency)
  relation = except(:includes, :eager_load, :preload, :select).select(join_dependency.columns + select_values)
  apply_join_dependency(relation, join_dependency)
end
find_first()

Source: show | on GitHub 

# File activerecord/lib/active_record/relation/finder_methods.rb, line 320
def find_first
  if loaded?
    @records.first
  else
    @first ||=
      if with_default_scope.order_values.empty? && primary_key
        order(arel_table[primary_key].asc).limit(1).to_a.first
      else
        limit(1).to_a.first
      end
  end
end
find_last()

Source: show | on GitHub 

# File activerecord/lib/active_record/relation/finder_methods.rb, line 333
def find_last
  if loaded?
    @records.last
  else
    @last ||=
      if offset_value || limit_value
        to_a.last
      else
        reverse_order.limit(1).to_a.first
      end
  end
end
find_one(id)

Source: show | on GitHub 

# File activerecord/lib/active_record/relation/finder_methods.rb, line 276
def find_one(id)
  id = id.id if ActiveRecord::Base === id

  column = columns_hash[primary_key]
  substitute = connection.substitute_at(column, bind_values.length)
  relation = where(table[primary_key].eq(substitute))
  relation.bind_values += [[column, id]]
  record = relation.take

  raise_record_not_found_exception!(id, 0, 1) unless record

  record
end
find_some(ids)

Source: show | on GitHub 

# File activerecord/lib/active_record/relation/finder_methods.rb, line 290
def find_some(ids)
  result = where(table[primary_key].in(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_take()

Source: show | on GitHub 

# File activerecord/lib/active_record/relation/finder_methods.rb, line 312
def find_take
  if loaded?
    @records.first
  else
    @take ||= limit(1).to_a.first
  end
end
find_with_associations()

Source: show | on GitHub 

# File activerecord/lib/active_record/relation/finder_methods.rb, line 204
def find_with_associations
  join_dependency = construct_join_dependency_for_association_find
  relation = construct_relation_for_association_find(join_dependency)
  rows = connection.select_all(relation, 'SQL', relation.bind_values.dup)
  join_dependency.instantiate(rows)
rescue ThrowResult
  []
end
find_with_ids(*ids)

Source: show | on GitHub 

# File activerecord/lib/active_record/relation/finder_methods.rb, line 259
def find_with_ids(*ids)
  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
end
using_limitable_reflections?(reflections)

Source: show | on GitHub 

# File activerecord/lib/active_record/relation/finder_methods.rb, line 346
def using_limitable_reflections?(reflections)
  reflections.none? { |r| r.collection? }
end