Active Record Relation
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Constants
CLAUSE_METHODS | = | [:where, :having, :from] |
INVALID_METHODS_FOR_DELETE_ALL | = | [:distinct] |
MULTI_VALUE_METHODS | = | [:includes, :eager_load, :preload, :select, :group, :order, :joins, :left_outer_joins, :references, :extending, :unscope, :optimizer_hints, :annotate] |
SINGLE_VALUE_METHODS | = | [:limit, :offset, :lock, :readonly, :reordering, :strict_loading, :reverse_order, :distinct, :create_with, :skip_query_cache] |
VALUE_METHODS | = | MULTI_VALUE_METHODS + SINGLE_VALUE_METHODS + CLAUSE_METHODS |
Attributes
[R] | klass | |
[R] | loaded | |
[R] | loaded? | |
[R] | model | |
[R] | predicate_builder | |
[RW] | skip_preloading_value | |
[R] | table |
Class Public methods
new(klass, table: klass.arel_table, predicate_builder: klass.predicate_builder, values: {}) Link
# File activerecord/lib/active_record/relation.rb, line 27 def initialize(klass, table: klass.arel_table, predicate_builder: klass.predicate_builder, values: {}) @klass = klass @table = table @values = values @loaded = false @predicate_builder = predicate_builder @delegate_to_klass = false @future_result = nil @records = nil end
Instance Public methods
==(other) Link
Compares two relations for equality.
any?() Link
Returns true if there are any records.
blank?() Link
Returns true if relation is blank.
cache_key(timestamp_column = "updated_at") Link
Returns a stable cache key that can be used to identify this query. The cache key is built with a fingerprint of the SQL query.
Product.where("name like ?", "%Cosmic Encounter%").cache_key
# => "products/query-1850ab3d302391b85b8693e941286659"
If ActiveRecord::Base.collection_cache_versioning
is turned off, as it was in Rails 6.0 and earlier, the cache key will also include a version.
ActiveRecord::Base.collection_cache_versioning = false
Product.where("name like ?", "%Cosmic Encounter%").cache_key
# => "products/query-1850ab3d302391b85b8693e941286659-1-20150714212553907087000"
You can also pass a custom timestamp column to fetch the timestamp of the last updated record.
Product.where("name like ?", "%Game%").cache_key(:last_reviewed_at)
cache_key_with_version() Link
Returns a cache key along with the version.
cache_version(timestamp_column = :updated_at) Link
Returns a cache version that can be used together with the cache key to form a recyclable caching scheme. The cache version is built with the number of records matching the query, and the timestamp of the last updated record. When a new record comes to match the query, or any of the existing records is updated or deleted, the cache version changes.
If the collection is loaded, the method will iterate through the records to generate the timestamp, otherwise it will trigger one SQL query like:
SELECT COUNT(*), MAX("products"."updated_at") FROM "products" WHERE (name like '%Cosmic Encounter%')
create(attributes = nil, &block) Link
Tries to create a new record with the same scoped attributes defined in the relation. Returns the initialized object if validation fails.
Expects arguments in the same format as ActiveRecord::Base.create.
Examples
users = User.where(name: 'Oscar')
users.create # => #<User id: 3, name: "Oscar", ...>
users.create(name: 'fxn')
users.create # => #<User id: 4, name: "fxn", ...>
users.create { |user| user.name = 'tenderlove' }
# => #<User id: 5, name: "tenderlove", ...>
users.create(name: nil) # validation on name
# => #<User id: nil, name: nil, ...>
create!(attributes = nil, &block) Link
Similar to create
, but calls create! on the base class. Raises an exception if a validation error occurs.
Expects arguments in the same format as ActiveRecord::Base.create!.
# File activerecord/lib/active_record/relation.rb, line 110 def create!(attributes = nil, &block) if attributes.is_a?(Array) attributes.collect { |attr| create!(attr, &block) } else block = current_scope_restoring_block(&block) scoping { _create!(attributes, &block) } end end
create_or_find_by(attributes, &block) Link
Attempts to create a record with the given attributes in a table that has a unique database constraint on one or several of its columns. If a row already exists with one or several of these unique constraints, the exception such an insertion would normally raise is caught, and the existing record with those attributes is found using find_by!.
This is similar to find_or_create_by
, but avoids the problem of stale reads between the SELECT and the INSERT, as that method needs to first query the table, then attempt to insert a row if none is found.
There are several drawbacks to create_or_find_by
, though:
-
The underlying table must have the relevant columns defined with unique database constraints.
-
A unique constraint violation may be triggered by only one, or at least less than all, of the given attributes. This means that the subsequent find_by! may fail to find a matching record, which will then raise an
ActiveRecord::RecordNotFound
exception, rather than a record with the given attributes. -
While we avoid the race condition between SELECT -> INSERT from
find_or_create_by
, we actually have another race condition between INSERT -> SELECT, which can be triggered if a DELETE between those two statements is run by another client. But for most applications, that’s a significantly less likely condition to hit. -
It relies on exception handling to handle control flow, which may be marginally slower.
-
The primary key may auto-increment on each create, even if it fails. This can accelerate the problem of running out of integers, if the underlying table is still stuck on a primary key of type int (note: All Rails apps since 5.1+ have defaulted to bigint, which is not liable to this problem).
This method will return a record if all given attributes are covered by unique constraints (unless the INSERT -> DELETE -> SELECT race condition is triggered), but if creation was attempted and failed due to validation errors it won’t be persisted, you get what create
returns in such situation.
create_or_find_by!(attributes, &block) Link
Like create_or_find_by
, but calls create! so an exception is raised if the created record is invalid.
delete_all() Link
Deletes the records without instantiating the records first, and hence not calling the #destroy method nor invoking callbacks. This is a single SQL DELETE statement that goes straight to the database, much more efficient than destroy_all
. Be careful with relations though, in particular :dependent
rules defined on associations are not honored. Returns the number of rows affected.
Post.where(person_id: 5).where(category: ['Something', 'Else']).delete_all
Both calls delete the affected posts all at once with a single DELETE statement. If you need to destroy dependent associations or call your before_*
or after_destroy
callbacks, use the destroy_all
method instead.
If an invalid method is supplied, delete_all
raises an ActiveRecordError:
Post.distinct.delete_all
# => ActiveRecord::ActiveRecordError: delete_all doesn't support distinct
# File activerecord/lib/active_record/relation.rb, line 601 def delete_all invalid_methods = INVALID_METHODS_FOR_DELETE_ALL.select do |method| value = @values[method] method == :distinct ? value : value&.any? end if invalid_methods.any? raise ActiveRecordError.new("delete_all doesn't support #{invalid_methods.join(', ')}") end arel = eager_loading? ? apply_join_dependency.arel : build_arel arel.source.left = table group_values_arel_columns = arel_columns(group_values.uniq) having_clause_ast = having_clause.ast unless having_clause.empty? stmt = arel.compile_delete(table[primary_key], having_clause_ast, group_values_arel_columns) klass.connection.delete(stmt, "#{klass} Delete All").tap { reset } end
delete_by(*args) Link
Finds and deletes all records matching the specified conditions. This is short-hand for relation.where(condition).delete_all
. Returns the number of rows affected.
If no record is found, returns 0
as zero rows were affected.
Person.delete_by(id: 13)
Person.delete_by(name: 'Spartacus', rating: 4)
Person.delete_by("published_at < ?", 2.weeks.ago)
destroy_all() Link
Destroys the records by instantiating each record and calling its #destroy method. Each object’s callbacks are executed (including :dependent
association options). Returns the collection of objects that were destroyed; each will be frozen, to reflect that no changes should be made (since they can’t be persisted).
Note: Instantiation, callback execution, and deletion of each record can be time consuming when you’re removing many records at once. It generates at least one SQL DELETE
query per record (or possibly more, to enforce your callbacks). If you want to delete many rows quickly, without concern for their associations or callbacks, use delete_all
instead.
Examples
Person.where(age: 0..18).destroy_all
destroy_by(*args) Link
Finds and destroys all records matching the specified conditions. This is short-hand for relation.where(condition).destroy_all
. Returns the collection of objects that were destroyed.
If no record is found, returns empty array.
Person.destroy_by(id: 13)
Person.destroy_by(name: 'Spartacus', rating: 4)
Person.destroy_by("published_at < ?", 2.weeks.ago)
eager_loading?() Link
Returns true if relation needs eager loading.
empty?() Link
Returns true if there are no records.
explain() Link
Runs EXPLAIN on the query or queries triggered by this relation and returns the result as a string. The string is formatted imitating the ones printed by the database shell.
Note that this method actually runs the queries, since the results of some are needed by the next ones when eager loading is going on.
Please see further details in the Active Record Query Interface guide.
find_or_create_by(attributes, &block) Link
Finds the first record with the given attributes, or creates a record with the attributes if one is not found:
# Find the first user named "Penélope" or create a new one.
User.find_or_create_by(first_name: 'Penélope')
# => #<User id: 1, first_name: "Penélope", last_name: nil>
# Find the first user named "Penélope" or create a new one.
# We already have one so the existing record will be returned.
User.find_or_create_by(first_name: 'Penélope')
# => #<User id: 1, first_name: "Penélope", last_name: nil>
# Find the first user named "Scarlett" or create a new one with
# a particular last name.
User.create_with(last_name: 'Johansson').find_or_create_by(first_name: 'Scarlett')
# => #<User id: 2, first_name: "Scarlett", last_name: "Johansson">
This method accepts a block, which is passed down to create
. The last example above can be alternatively written this way:
# Find the first user named "Scarlett" or create a new one with a
# particular last name.
User.find_or_create_by(first_name: 'Scarlett') do |user|
user.last_name = 'Johansson'
end
# => #<User id: 2, first_name: "Scarlett", last_name: "Johansson">
This method always returns a record, but if creation was attempted and failed due to validation errors it won’t be persisted, you get what create
returns in such situation.
Please note this method is not atomic, it runs first a SELECT, and if there are no results an INSERT is attempted. If there are other threads or processes there is a race condition between both calls and it could be the case that you end up with two similar records.
If this might be a problem for your application, please see create_or_find_by
.
find_or_create_by!(attributes, &block) Link
Like find_or_create_by
, but calls create! so an exception is raised if the created record is invalid.
find_or_initialize_by(attributes, &block) Link
Like find_or_create_by
, but calls new instead of create.
initialize_copy(other) Link
inspect() Link
# File activerecord/lib/active_record/relation.rb, line 794 def inspect subject = loaded? ? records : annotate("loading for inspect") entries = subject.take([limit_value, 11].compact.min).map!(&:inspect) entries[10] = "..." if entries.size == 11 "#<#{self.class.name} [#{entries.join(', ')}]>" end
joined_includes_values() Link
Joins that are also marked for preloading. In which case we should just eager load them. Note that this is a naive implementation because we could have strings and symbols which represent the same association, but that aren’t matched by this. Also, we could have nested hashes which partially match, e.g. { a: :b } & { a: [:b, :c] }
load(&block) Link
Causes the records to be loaded from the database if they have not been loaded already. You can use this if for some reason you need to explicitly load some records before actually using them. The return value is the relation itself, not the records.
Post.where(published: true).load # => #<ActiveRecord::Relation>
load_async() Link
Schedule the query to be performed from a background thread pool.
Post.where(published: true).load_async # => #<ActiveRecord::Relation>
When the Relation
is iterated, if the background query wasn’t executed yet, it will be performed by the foreground thread.
Note that config.active_record.async_query_executor must be configured for queries to actually be executed concurrently. Otherwise it defaults to executing them in the foreground.
load_async
will also fall back to executing in the foreground in the test environment when transactional fixtures are enabled.
If the query was actually executed in the background, the Active Record logs will show it by prefixing the log line with ASYNC
:
ASYNC Post Load (0.0ms) (db time 2ms) SELECT "posts".* FROM "posts" LIMIT 100
# File activerecord/lib/active_record/relation.rb, line 664 def load_async return load if !connection.async_enabled? unless loaded? result = exec_main_query(async: connection.current_transaction.closed?) if result.is_a?(Array) @records = result else @future_result = result end @loaded = true end self end
many?() Link
Returns true if there is more than one record.
new(attributes = nil, &block) Link
Initializes new record from relation while maintaining the current scope.
Expects arguments in the same format as ActiveRecord::Base.new.
users = User.where(name: 'DHH')
user = users.new # => #<User id: nil, name: "DHH", created_at: nil, updated_at: nil>
You can also pass a block to new with the new record as argument:
user = users.new { |user| user.name = 'Oscar' }
user.name # => Oscar
none?() Link
Returns true if there are no records.
one?() Link
Returns true if there is exactly one record.
pretty_print(q) Link
reload() Link
Forces reloading of relation.
reset() Link
# File activerecord/lib/active_record/relation.rb, line 708 def reset @future_result&.cancel @future_result = nil @delegate_to_klass = false @to_sql = @arel = @loaded = @should_eager_load = nil @offsets = @take = nil @cache_keys = nil @cache_versions = nil @records = nil self end
scheduled?() Link
Returns true
if the relation was scheduled on the background thread pool.
scope_for_create() Link
scoping(all_queries: nil, &block) Link
Scope all queries to the current scope.
Comment.where(post_id: 1).scoping do
Comment.first
end
# => SELECT "comments".* FROM "comments" WHERE "comments"."post_id" = 1 ORDER BY "comments"."id" ASC LIMIT 1
If all_queries: true
is passed, scoping will apply to all queries for the relation including update
and delete
on instances. Once all_queries
is set to true it cannot be set to false in a nested block.
Please check unscoped if you want to remove all previous scopes (including the default_scope) during the execution of a block.
# File activerecord/lib/active_record/relation.rb, line 421 def scoping(all_queries: nil, &block) registry = klass.scope_registry if global_scope?(registry) && all_queries == false raise ArgumentError, "Scoping is set to apply to all queries and cannot be unset in a nested block." elsif already_in_scope?(registry) yield else _scoping(self, registry, all_queries, &block) end end
size() Link
Returns size of the records.
to_sql() Link
Returns sql statement for the relation.
User.where(name: 'Oscar').to_sql
# => SELECT "users".* FROM "users" WHERE "users"."name" = 'Oscar'
# File activerecord/lib/active_record/relation.rb, line 724 def to_sql @to_sql ||= if eager_loading? apply_join_dependency do |relation, join_dependency| relation = join_dependency.apply_column_aliases(relation) relation.to_sql end else conn = klass.connection conn.unprepared_statement { conn.to_sql(arel) } end end
touch_all(*names, time: nil) Link
Touches all records in the current relation, setting the updated_at
/updated_on
attributes to the current time or the time specified. It does not instantiate the involved models, and it does not trigger Active Record callbacks or validations. This method can be passed attribute names and an optional time argument. If attribute names are passed, they are updated along with updated_at
/updated_on
attributes. If no time argument is passed, the current time is used as default.
Examples
# Touch all records
Person.all.touch_all
# => "UPDATE \"people\" SET \"updated_at\" = '2018-01-04 22:55:23.132670'"
# Touch multiple records with a custom attribute
Person.all.touch_all(:created_at)
# => "UPDATE \"people\" SET \"updated_at\" = '2018-01-04 22:55:23.132670', \"created_at\" = '2018-01-04 22:55:23.132670'"
# Touch multiple records with a specified time
Person.all.touch_all(time: Time.new(2020, 5, 16, 0, 0, 0))
# => "UPDATE \"people\" SET \"updated_at\" = '2020-05-16 00:00:00'"
# Touch records with scope
Person.where(name: 'David').touch_all
# => "UPDATE \"people\" SET \"updated_at\" = '2018-01-04 22:55:23.132670' WHERE \"people\".\"name\" = 'David'"
update_all(updates) Link
Updates all records in the current relation with details given. This method constructs a single SQL UPDATE statement and sends it straight to the database. It does not instantiate the involved models and it does not trigger Active Record callbacks or validations. However, values passed to update_all
will still go through Active Record’s normal type casting and serialization. Returns the number of rows affected.
Note: As Active Record callbacks are not triggered, this method will not automatically update updated_at
/updated_on
columns.
Parameters
-
updates
- A string, array, or hash representing the SET part of an SQL statement.
Examples
# Update all customers with the given attributes
Customer.update_all wants_email: true
# Update all books with 'Rails' in their title
Book.where('title LIKE ?', '%Rails%').update_all(author: 'David')
# Update all books that match conditions, but limit it to 5 ordered by date
Book.where('title LIKE ?', '%Rails%').order(:created_at).limit(5).update_all(author: 'David')
# Update all invoices and set the number column to its id value.
Invoice.update_all('number = id')
# File activerecord/lib/active_record/relation.rb, line 464 def update_all(updates) raise ArgumentError, "Empty list of attributes to change" if updates.blank? if updates.is_a?(Hash) if klass.locking_enabled? && !updates.key?(klass.locking_column) && !updates.key?(klass.locking_column.to_sym) attr = table[klass.locking_column] updates[attr.name] = _increment_attribute(attr) end values = _substitute_values(updates) else values = Arel.sql(klass.sanitize_sql_for_assignment(updates, table.name)) end arel = eager_loading? ? apply_join_dependency.arel : build_arel arel.source.left = table group_values_arel_columns = arel_columns(group_values.uniq) having_clause_ast = having_clause.ast unless having_clause.empty? stmt = arel.compile_update(values, table[primary_key], having_clause_ast, group_values_arel_columns) klass.connection.update(stmt, "#{klass} Update All").tap { reset } end
update_counters(counters) Link
Updates the counters of the records in the current relation.
Parameters
-
counter
- AHash
containing the names of the fields to update as keys and the amount to update as values. -
:touch
option - Touch the timestamp columns when updating. -
If attributes names are passed, they are updated along with update_at/on attributes.
Examples
# For Posts by a given author increment the comment_count by 1.
Post.where(author_id: author.id).update_counters(comment_count: 1)
# File activerecord/lib/active_record/relation.rb, line 516 def update_counters(counters) touch = counters.delete(:touch) updates = {} counters.each do |counter_name, value| attr = table[counter_name] updates[attr.name] = _increment_attribute(attr, value) end if touch names = touch if touch != true names = Array.wrap(names) options = names.extract_options! touch_updates = klass.touch_attributes_with_time(*names, **options) updates.merge!(touch_updates) unless touch_updates.empty? end update_all updates end