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Constants
ONE_AS_ONE | = | "1 AS one" |
Instance Public methods
exists?(conditions = :none) Link
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 thesewhere
-style conditions (such as['name LIKE ?', "%#{query}%"]
). -
Hash
- Finds the record that matches thesewhere
-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 activerecord/lib/active_record/relation/finder_methods.rb, line 357 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 do with_connection do |c| c.select_rows(relation.arel, "#{name} Exists?").size == 1 end end end
fifth() Link
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
fifth!() Link
Same as fifth
but raises ActiveRecord::RecordNotFound
if no record is found.
find(*args) Link
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 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), 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 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.
Edge Cases
Person.find(37) # raises ActiveRecord::RecordNotFound exception if the record with the given ID does not exist.
Person.find([37]) # raises ActiveRecord::RecordNotFound exception if the record with the given ID in the input array does not exist.
Person.find(nil) # raises ActiveRecord::RecordNotFound exception if the argument is nil.
Person.find([]) # returns an empty array if the argument is an empty array.
Person.find # raises ActiveRecord::RecordNotFound exception if the argument is not provided.
find_by(arg, *args) Link
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
find_by!(arg, *args) Link
Like find_by
, except that if no record is found, raises an ActiveRecord::RecordNotFound
error.
find_sole_by(arg, *args) Link
Finds the sole matching record. Raises ActiveRecord::RecordNotFound
if no record is found. Raises ActiveRecord::SoleRecordExceeded
if more than one record is found.
Product.find_sole_by(["price = %?", price])
first(limit = nil) Link
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
first!() Link
Same as first
but raises ActiveRecord::RecordNotFound
if no record is found. Note that first!
accepts no arguments.
forty_two() Link
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
forty_two!() Link
Same as forty_two
but raises ActiveRecord::RecordNotFound
if no record is found.
fourth() Link
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
fourth!() Link
Same as fourth
but raises ActiveRecord::RecordNotFound
if no record is found.
include?(record) Link
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 activerecord/lib/active_record/relation/finder_methods.rb, line 389 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) Link
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>]
last!() Link
Same as last
but raises ActiveRecord::RecordNotFound
if no record is found. Note that last!
accepts no arguments.
second() Link
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
second!() Link
Same as second
but raises ActiveRecord::RecordNotFound
if no record is found.
second_to_last() Link
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
second_to_last!() Link
Same as second_to_last
but raises ActiveRecord::RecordNotFound
if no record is found.
sole() Link
Finds the sole matching record. Raises ActiveRecord::RecordNotFound
if no record is found. Raises ActiveRecord::SoleRecordExceeded
if more than one record is found.
Product.where(["price = %?", price]).sole
take(limit = nil) Link
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
take!() Link
Same as take
but raises ActiveRecord::RecordNotFound
if no record is found. Note that take!
accepts no arguments.
third() Link
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
third!() Link
Same as third
but raises ActiveRecord::RecordNotFound
if no record is found.
third_to_last() Link
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
third_to_last!() Link
Same as third_to_last
but raises ActiveRecord::RecordNotFound
if no record is found.