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
find
-style conditions (such as['name LIKE ?', "%#{query}%"]
). -
Hash - Finds the record that matches these
find
-style conditions (such as{name: 'David'}
). -
false
- Returns alwaysfalse
. -
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, <<-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
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
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 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.
# File lib/active_record/relation/finder_methods.rb, line 64 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 77 def find_by(arg, *args) where(arg, *args).take rescue ::RangeError nil 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 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
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
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 233 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 239 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 201 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 207 def fourth! fourth || raise_record_not_found_exception! 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? || 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
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
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
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
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
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
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
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
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
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
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
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
# File lib/active_record/relation/finder_methods.rb, line 399 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
# File lib/active_record/relation/finder_methods.rb, line 390 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
# File lib/active_record/relation/finder_methods.rb, line 395 def construct_relation_for_association_calculations apply_join_dependency(self, construct_join_dependency(joins_values)) end
# File lib/active_record/relation/finder_methods.rb, line 377 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
# File lib/active_record/relation/finder_methods.rb, line 562 def find_last(limit) limit ? records.last(limit) : records.last end
# File lib/active_record/relation/finder_methods.rb, line 520 def find_nth(index) @offsets[offset_index + index] ||= find_nth_with_limit(index, 1).first end
# File lib/active_record/relation/finder_methods.rb, line 543 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
# File lib/active_record/relation/finder_methods.rb, line 524 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
# File lib/active_record/relation/finder_methods.rb, line 449 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 465 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 489 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 504 def find_take if loaded? records.first else @take ||= limit(1).records.first end end
# File lib/active_record/relation/finder_methods.rb, line 512 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 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) yield relation, join_dependency end
# File lib/active_record/relation/finder_methods.rb, line 428 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
# File lib/active_record/relation/finder_methods.rb, line 413 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
# File lib/active_record/relation/finder_methods.rb, line 354 def offset_index offset_value || 0 end
# File lib/active_record/relation/finder_methods.rb, line 424 def using_limitable_reflections?(reflections) reflections.none?(&:collection?) end