module ActiveRecord::FinderMethods
Constants
- ONE_AS_ONE
Public Instance Methods
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 alwaysfalse
. -
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 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? Person.where(name: 'Spartacus', rating: 4).exists?
# 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 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
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 216 def fifth find_nth 4 end
Same as fifth
but raises ActiveRecord::RecordNotFound
if no record is found.
# File lib/active_record/relation/finder_methods.rb, line 222 def fifth! fifth || raise_record_not_found_exception! 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 cannot be found for the requested ids, then ActiveRecord::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) 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 are in the same order as the ids you provide. If you want the results to be sorted by database, you can use ActiveRecord::QueryMethods#where
method and provide an explicit ActiveRecord::QueryMethods#order
option. But ActiveRecord::QueryMethods#where
method doesn't raise ActiveRecord::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.
# File lib/active_record/relation/finder_methods.rb, line 67 def find(*args) return super if block_given? find_with_ids(*args) 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
# File lib/active_record/relation/finder_methods.rb, line 80 def find_by(arg, *args) where(arg, *args).take end
Like find_by
, except that if no record is found, raises an ActiveRecord::RecordNotFound
error.
# File lib/active_record/relation/finder_methods.rb, line 86 def find_by!(arg, *args) where(arg, *args).take! 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
# File lib/active_record/relation/finder_methods.rb, line 116 def first(limit = nil) check_reorder_deprecation unless loaded? if limit find_nth_with_limit(0, limit) else find_nth 0 end end
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
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 232 def forty_two find_nth 41 end
Same as forty_two
but raises ActiveRecord::RecordNotFound
if no record is found.
# File lib/active_record/relation/finder_methods.rb, line 238 def forty_two! forty_two || raise_record_not_found_exception! 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
# File lib/active_record/relation/finder_methods.rb, line 200 def fourth find_nth 3 end
Same as fourth
but raises ActiveRecord::RecordNotFound
if no record is found.
# File lib/active_record/relation/finder_methods.rb, line 206 def fourth! fourth || raise_record_not_found_exception! end
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?
.
# File lib/active_record/relation/finder_methods.rb, line 328 def include?(record) if loaded? || offset_value || limit_value || having_clause.any? records.include?(record) else record.is_a?(klass) && exists?(record.id) end 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>]
# File lib/active_record/relation/finder_methods.rb, line 147 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
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 158 def last! last || raise_record_not_found_exception! 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
# File lib/active_record/relation/finder_methods.rb, line 168 def second find_nth 1 end
Same as second
but raises ActiveRecord::RecordNotFound
if no record is found.
# File lib/active_record/relation/finder_methods.rb, line 174 def second! second || raise_record_not_found_exception! 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
# File lib/active_record/relation/finder_methods.rb, line 264 def second_to_last find_nth_from_last 2 end
Same as second_to_last
but raises ActiveRecord::RecordNotFound
if no record is found.
# File lib/active_record/relation/finder_methods.rb, line 270 def second_to_last! second_to_last || raise_record_not_found_exception! 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
# File lib/active_record/relation/finder_methods.rb, line 97 def take(limit = nil) limit ? find_take_with_limit(limit) : find_take end
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 103 def take! take || raise_record_not_found_exception! 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
# File lib/active_record/relation/finder_methods.rb, line 184 def third find_nth 2 end
Same as third
but raises ActiveRecord::RecordNotFound
if no record is found.
# File lib/active_record/relation/finder_methods.rb, line 190 def third! third || raise_record_not_found_exception! 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
# File lib/active_record/relation/finder_methods.rb, line 248 def third_to_last find_nth_from_last 3 end
Same as third_to_last
but raises ActiveRecord::RecordNotFound
if no record is found.
# File lib/active_record/relation/finder_methods.rb, line 254 def third_to_last! third_to_last || raise_record_not_found_exception! end
Private Instance Methods
# File lib/active_record/relation/finder_methods.rb, line 397 def apply_join_dependency(eager_loading: group_values.empty?) join_dependency = construct_join_dependency( eager_load_values | includes_values, Arel::Nodes::OuterJoin ) relation = except(:includes, :eager_load, :preload).joins!(join_dependency) if eager_loading && !( using_limitable_reflections?(join_dependency.reflections) && using_limitable_reflections?( construct_join_dependency( select_association_list(joins_values).concat( select_association_list(left_outer_joins_values) ), nil ).reflections ) ) if has_limit_or_offset? limited_ids = limited_ids_for(relation) limited_ids.empty? ? relation.none! : relation.where!(primary_key => limited_ids) end relation.limit_value = relation.offset_value = nil end if block_given? yield relation, join_dependency else relation end end
# File lib/active_record/relation/finder_methods.rb, line 367 def check_reorder_deprecation if !order_values.empty? && order_values.all?(&:blank?) blank_value = order_values.first ActiveSupport::Deprecation.warn(<<~MSG.squish) `.reorder(#{blank_value.inspect})` with `.first` / `.first!` no longer takes non-deterministic result in Rails 7.0. To continue taking non-deterministic result, use `.take` / `.take!` instead. MSG end end
# File lib/active_record/relation/finder_methods.rb, line 378 def construct_relation_for_exists(conditions) conditions = sanitize_forbidden_attributes(conditions) if distinct_value && offset_value relation = except(:order).limit!(1) else relation = except(:select, :distinct, :order)._select!(ONE_AS_ONE).limit!(1) end case conditions when Array, Hash relation.where!(conditions) unless conditions.empty? else relation.where!(primary_key => conditions) unless conditions == :none end relation end
# File lib/active_record/relation/finder_methods.rb, line 574 def find_last(limit) limit ? records.last(limit) : records.last end
# File lib/active_record/relation/finder_methods.rb, line 536 def find_nth(index) @offsets ||= {} @offsets[index] ||= find_nth_with_limit(index, 1).first end
# File lib/active_record/relation/finder_methods.rb, line 560 def find_nth_from_last(index) if loaded? records[-index] else relation = ordered_relation if equal?(relation) || has_limit_or_offset? relation.records[-index] else relation.last(index)[-index] end end end
# File lib/active_record/relation/finder_methods.rb, line 541 def find_nth_with_limit(index, limit) if loaded? records[index, limit] || [] else relation = ordered_relation if limit_value limit = [limit_value - index, limit].min end if limit > 0 relation = relation.offset((offset_value || 0) + index) unless index.zero? relation.limit(limit).to_a else [] end end end
# File lib/active_record/relation/finder_methods.rb, line 465 def find_one(id) if ActiveRecord::Base === id raise ArgumentError, <<-MSG.squish You are passing an instance of ActiveRecord::Base to `find`. Please pass the id of the object by calling `.id`. MSG end relation = where(primary_key => id) record = relation.take raise_record_not_found_exception!(id, 0, 1) unless record record end
# File lib/active_record/relation/finder_methods.rb, line 481 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
# File lib/active_record/relation/finder_methods.rb, line 505 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
# File lib/active_record/relation/finder_methods.rb, line 520 def find_take if loaded? records.first else @take ||= limit(1).records.first end end
# File lib/active_record/relation/finder_methods.rb, line 528 def find_take_with_limit(limit) if loaded? records.take(limit) else limit(limit).to_a end end
# File lib/active_record/relation/finder_methods.rb, line 443 def find_with_ids(*ids) raise UnknownPrimaryKey.new(@klass) if primary_key.nil? expects_array = ids.first.kind_of?(Array) return [] if expects_array && ids.first.empty? ids = ids.flatten.compact.uniq model_name = @klass.name case ids.size when 0 error_message = "Couldn't find #{model_name} without an ID" raise RecordNotFound.new(error_message, model_name, primary_key) when 1 result = find_one(ids.first) expects_array ? [ result ] : result else find_some(ids) end end
# File lib/active_record/relation/finder_methods.rb, line 427 def limited_ids_for(relation) values = @klass.connection.columns_for_distinct( connection.visitor.compile(table[primary_key]), relation.order_values ) relation = relation.except(:select).select(values).distinct! id_rows = skip_query_cache_if_necessary { @klass.connection.select_rows(relation.arel, "SQL") } id_rows.map(&:last) end
# File lib/active_record/relation/finder_methods.rb, line 578 def ordered_relation if order_values.empty? && (implicit_order_column || primary_key) if implicit_order_column && primary_key && implicit_order_column != primary_key order(table[implicit_order_column].asc, table[primary_key].asc) else order(table[implicit_order_column || primary_key].asc) end else self end end
# File lib/active_record/relation/finder_methods.rb, line 439 def using_limitable_reflections?(reflections) reflections.none?(&:collection?) end