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Module: ActiveRecord::FinderMethods

Relationships & Source Files
Extension / Inclusion / Inheritance Descendants
Included In:
ActiveRecord::AssociationRelation, Associations::CollectionProxy, ActiveRecord::DisableJoinsAssociationRelation, Relation
Defined in: activerecord/lib/active_record/relation/finder_methods.rb

Constant Summary

Instance Method Summary

Instance Method Details

#exists?(conditions = :none) ⇒ Boolean

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 where-style conditions (such as ['name LIKE ?', "%#{query}%"]).

  • ::Hash - Finds the record that matches these where-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 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?
[ GitHub ]

  
# File 'activerecord/lib/active_record/relation/finder_methods.rb', line 349

def exists?(conditions = :none)
  return false if @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)
  return false if relation.where_clause.contradiction?

  skip_query_cache_if_necessary { connection.select_rows(relation.arel, "#{name} Exists?").size == 1 }
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
[ GitHub ]

  
# File 'activerecord/lib/active_record/relation/finder_methods.rb', line 263

def fifth
  find_nth 4
end

#fifth!

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

[ GitHub ]

  
# File 'activerecord/lib/active_record/relation/finder_methods.rb', line 269

def fifth!
  fifth || raise_record_not_found_exception!
end

#find(*args)

Find by id - This can either be a specific id (ID), a list of ids (ID, ID, ID), or an array of ids ([ID, ID, ID]). ID refers to an “identifier”. For models with a single-column primary key, ID will be a single value, and for models with a composite primary key, it will be an array of values. If one or more records cannot be found for the requested ids, then 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), or with composite primary key [7, 17]
Person.find([1])        # returns an array for the object with ID = 1
Person.where("administrator = 1").order("created_on DESC").find(1)

Find a record for a composite primary key model

TravelRoute.primary_key = [:origin, :destination]

TravelRoute.find(["Ottawa", "London"])
#=> #<TravelRoute origin: "Ottawa", destination: "London">

TravelRoute.find([["Paris", "Montreal"]])
#=> [#<TravelRoute origin: "Paris", destination: "Montreal">]

TravelRoute.find(["New York", "Las Vegas"], ["New York", "Portland"])
#=> [
     #<TravelRoute origin: "New York", destination: "Las Vegas">,
     #<TravelRoute origin: "New York", destination: "Portland">
   ]

TravelRoute.find([["Berlin", "London"], ["Barcelona", "Lisbon"]])
#=> [
     #<TravelRoute origin: "Berlin", destination: "London">,
     #<TravelRoute origin: "Barcelona", destination: "Lisbon">
   ]

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 QueryMethods#where method and provide an explicit QueryMethods#order option. But QueryMethods#where method doesn’t raise 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.
[ GitHub ]

  
# File 'activerecord/lib/active_record/relation/finder_methods.rb', line 90

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
[ GitHub ]

  
# File 'activerecord/lib/active_record/relation/finder_methods.rb', line 103

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 RecordNotFound error.

[ GitHub ]

  
# File 'activerecord/lib/active_record/relation/finder_methods.rb', line 109

def find_by!(arg, *args)
  where(arg, *args).take!
end

#find_sole_by(arg, *args)

Finds the sole matching record. Raises RecordNotFound if no record is found. Raises SoleRecordExceeded if more than one record is found.

Product.find_sole_by(["price = %?", price])
[ GitHub ]

  
# File 'activerecord/lib/active_record/relation/finder_methods.rb', line 152

def find_sole_by(arg, *args)
  where(arg, *args).sole
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
[ GitHub ]

  
# File 'activerecord/lib/active_record/relation/finder_methods.rb', line 165

def first(limit = nil)
  if limit
    find_nth_with_limit(0, limit)
  else
    find_nth 0
  end
end

#first!

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

[ GitHub ]

  
# File 'activerecord/lib/active_record/relation/finder_methods.rb', line 175

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
[ GitHub ]

  
# File 'activerecord/lib/active_record/relation/finder_methods.rb', line 279

def forty_two
  find_nth 41
end

#forty_two!

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

[ GitHub ]

  
# File 'activerecord/lib/active_record/relation/finder_methods.rb', line 285

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
[ GitHub ]

  
# File 'activerecord/lib/active_record/relation/finder_methods.rb', line 247

def fourth
  find_nth 3
end

#fourth!

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

[ GitHub ]

  
# File 'activerecord/lib/active_record/relation/finder_methods.rb', line 253

def fourth!
  fourth || raise_record_not_found_exception!
end

#include?(record) ⇒ Boolean Also known as: #member?

Returns true if the relation contains the given record or false otherwise.

No query is performed if the relation is loaded; the given record is compared to the records in memory. If the relation is unloaded, an efficient existence query is performed, as in #exists?.

[ GitHub ]

  
# File 'activerecord/lib/active_record/relation/finder_methods.rb', line 377

def include?(record)
  # The existing implementation relies on receiving an Active Record instance as the input parameter named record.
  # Any non-Active Record object passed to this implementation is guaranteed to return `false`.
  return false unless record.is_a?(klass)

  if loaded? || offset_value || limit_value || having_clause.any?
    records.include?(record)
  else
    id = if record.class.composite_primary_key?
      record.class.primary_key.zip(record.id).to_h
    else
      record.id
    end

    exists?(id)
  end
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>]
[ GitHub ]

  
# File 'activerecord/lib/active_record/relation/finder_methods.rb', line 194

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 RecordNotFound if no record is found. Note that #last! accepts no arguments.

[ GitHub ]

  
# File 'activerecord/lib/active_record/relation/finder_methods.rb', line 205

def last!
  last || raise_record_not_found_exception!
end

#member?(record)

Alias for #include?.

[ GitHub ]

  
# File 'activerecord/lib/active_record/relation/finder_methods.rb', line 395

alias :member? :include?

#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
[ GitHub ]

  
# File 'activerecord/lib/active_record/relation/finder_methods.rb', line 215

def second
  find_nth 1
end

#second!

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

[ GitHub ]

  
# File 'activerecord/lib/active_record/relation/finder_methods.rb', line 221

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
[ GitHub ]

  
# File 'activerecord/lib/active_record/relation/finder_methods.rb', line 311

def second_to_last
  find_nth_from_last 2
end

#second_to_last!

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

[ GitHub ]

  
# File 'activerecord/lib/active_record/relation/finder_methods.rb', line 317

def second_to_last!
  second_to_last || raise_record_not_found_exception!
end

#sole

Finds the sole matching record. Raises RecordNotFound if no record is found. Raises SoleRecordExceeded if more than one record is found.

Product.where(["price = %?", price]).sole
[ GitHub ]

  
# File 'activerecord/lib/active_record/relation/finder_methods.rb', line 135

def sole
  found, undesired = first(2)

  if found.nil?
    raise_record_not_found_exception!
  elsif undesired.present?
    raise ActiveRecord::SoleRecordExceeded.new(self)
  else
    found
  end
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
[ GitHub ]

  
# File 'activerecord/lib/active_record/relation/finder_methods.rb', line 120

def take(limit = nil)
  limit ? find_take_with_limit(limit) : find_take
end

#take!

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

[ GitHub ]

  
# File 'activerecord/lib/active_record/relation/finder_methods.rb', line 126

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
[ GitHub ]

  
# File 'activerecord/lib/active_record/relation/finder_methods.rb', line 231

def third
  find_nth 2
end

#third!

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

[ GitHub ]

  
# File 'activerecord/lib/active_record/relation/finder_methods.rb', line 237

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
[ GitHub ]

  
# File 'activerecord/lib/active_record/relation/finder_methods.rb', line 295

def third_to_last
  find_nth_from_last 3
end

#third_to_last!

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

[ GitHub ]

  
# File 'activerecord/lib/active_record/relation/finder_methods.rb', line 301

def third_to_last!
  third_to_last || raise_record_not_found_exception!
end