Module: ActiveRecord::FinderMethods

Included in:
Relation
Defined in:
lib/active_record/relation/finder_methods.rb

Constant Summary collapse

ONE_AS_ONE =
"1 AS one"

Instance Method Summary collapse

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 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?

Returns:

  • (Boolean)

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# File 'lib/active_record/relation/finder_methods.rb', line 302

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

  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

#fifthObject

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

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# File 'lib/active_record/relation/finder_methods.rb', line 217

def fifth
  find_nth 4
end

#fifth!Object

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


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# File 'lib/active_record/relation/finder_methods.rb', line 223

def fifth!
  fifth || raise_record_not_found_exception!
end

#find(*args) ⇒ Object

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 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.

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# 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) ⇒ Object

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

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# 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) ⇒ Object

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


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# 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) ⇒ Object

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

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# 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!Object

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


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# File 'lib/active_record/relation/finder_methods.rb', line 128

def first!
  first || raise_record_not_found_exception!
end

#forty_twoObject

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

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# File 'lib/active_record/relation/finder_methods.rb', line 233

def forty_two
  find_nth 41
end

#forty_two!Object

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


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# File 'lib/active_record/relation/finder_methods.rb', line 239

def forty_two!
  forty_two || raise_record_not_found_exception!
end

#fourthObject

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

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# File 'lib/active_record/relation/finder_methods.rb', line 201

def fourth
  find_nth 3
end

#fourth!Object

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


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# File 'lib/active_record/relation/finder_methods.rb', line 207

def fourth!
  fourth || raise_record_not_found_exception!
end

#last(limit = nil) ⇒ Object

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>]

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# 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!Object

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


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# File 'lib/active_record/relation/finder_methods.rb', line 159

def last!
  last || raise_record_not_found_exception!
end

#raise_record_not_found_exception!(ids = nil, result_size = nil, expected_size = nil, key = primary_key) ⇒ Object

This method is called whenever no records are found with either a single id or multiple ids and raises an ActiveRecord::RecordNotFound exception.

The error message is different depending on whether a single id or multiple ids are provided. If multiple ids are provided, then the number of results obtained should be provided in the result_size argument and the expected number of results should be provided in the expected_size argument.


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# File 'lib/active_record/relation/finder_methods.rb', line 332

def raise_record_not_found_exception!(ids = nil, result_size = nil, expected_size = nil, key = primary_key) # :nodoc:
  conditions = arel.where_sql(@klass.arel_engine)
  conditions = " [#{conditions}]" if conditions
  name = @klass.name

  if ids.nil?
    error = "Couldn't find #{name}"
    error << " with#{conditions}" if conditions
    raise RecordNotFound.new(error, name)
  elsif Array(ids).size == 1
    error = "Couldn't find #{name} with '#{key}'=#{ids}#{conditions}"
    raise RecordNotFound.new(error, name, key, ids)
  else
    error = "Couldn't find all #{name.pluralize} with '#{key}': "
    error << "(#{ids.join(", ")})#{conditions} (found #{result_size} results, but was looking for #{expected_size})"

    raise RecordNotFound.new(error, name, primary_key, ids)
  end
end

#secondObject

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

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# File 'lib/active_record/relation/finder_methods.rb', line 169

def second
  find_nth 1
end

#second!Object

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


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

def second!
  second || raise_record_not_found_exception!
end

#second_to_lastObject

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

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# File 'lib/active_record/relation/finder_methods.rb', line 265

def second_to_last
  find_nth_from_last 2
end

#second_to_last!Object

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


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# 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) ⇒ Object

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

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# File 'lib/active_record/relation/finder_methods.rb', line 99

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

#take!Object

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


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# File 'lib/active_record/relation/finder_methods.rb', line 105

def take!
  take || raise_record_not_found_exception!
end

#thirdObject

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

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# File 'lib/active_record/relation/finder_methods.rb', line 185

def third
  find_nth 2
end

#third!Object

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


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# File 'lib/active_record/relation/finder_methods.rb', line 191

def third!
  third || raise_record_not_found_exception!
end

#third_to_lastObject

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

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# File 'lib/active_record/relation/finder_methods.rb', line 249

def third_to_last
  find_nth_from_last 3
end

#third_to_last!Object

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


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# File 'lib/active_record/relation/finder_methods.rb', line 255

def third_to_last!
  third_to_last || raise_record_not_found_exception!
end