Compares two relations for equality.

Returns true if there are any records.

When a pattern argument is given, this method checks whether elements in the Enumerable match the pattern via the case-equality operator (===).

posts.any?(Post) # => true or false

Returns true if relation is blank.

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)

Returns a cache key along with the version.

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%')

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, ...>

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!.

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 tries to create the record first. As such it is better suited for cases where the record is most likely not to exist yet.

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).

• Columns with unique database constraints should not have uniqueness validations defined, otherwise create will fail due to validation errors and find_by will never be called.

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.

Like create_or_find_by, but calls create! so an exception is raised if the created record is invalid.

Deletes the row with a primary key matching the id argument, using an SQL DELETE statement, and returns the number of rows deleted. Active Record objects are not instantiated, so the object’s callbacks are not executed, including any :dependent association options.

You can delete multiple rows at once by passing an Array of ids.

Note: Although it is often much faster than the alternative, destroy, skipping callbacks might bypass business logic in your application that ensures referential integrity or performs other essential jobs.

Examples

# Delete a single row
Todo.delete(1)

# Delete multiple rows
Todo.delete([2,3,4])

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

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 an object (or multiple objects) that has the given id. The object is instantiated first, therefore all callbacks and filters are fired off before the object is deleted. This method is less efficient than delete but allows cleanup methods and other actions to be run.

This essentially finds the object (or multiple objects) with the given id, creates a new object from the attributes, and then calls destroy on it.

Parameters

• id - This should be the id or an array of ids to be destroyed.

Examples

# Destroy a single object
Todo.destroy(1)

# Destroy multiple objects
todos = [1,2,3]
Todo.destroy(todos)

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

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)

Returns true if relation needs eager loading.

Returns true if there are no records.

Serializes the relation objects Array.

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.

User.all.explain
# EXPLAIN SELECT `users`.* FROM `users`
# ...

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.

To run EXPLAIN on queries created by first, pluck and count, call these methods on explain:

User.all.explain.count
# EXPLAIN SELECT COUNT(*) FROM `users`
# ...

The column name can be passed if required:

User.all.explain.maximum(:id)
# EXPLAIN SELECT MAX(`users`.`id`) FROM `users`
# ...

Please see further details in the Active Record Query Interface guide.

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.

If creation failed because of a unique constraint, this method will assume it encountered a race condition and will try finding the record once more. If somehow the second find still does not find a record because a concurrent DELETE happened, it will then raise an ActiveRecord::RecordNotFound exception.

Please note this method is not atomic, it runs first a SELECT, and if there are no results an INSERT is attempted. So if the table doesn’t have a relevant unique constraint it could be the case that you end up with two or more similar records.

Like find_or_create_by, but calls create! so an exception is raised if the created record is invalid.

Like find_or_create_by, but calls new instead of create.

Inserts a single record into the database in a single SQL INSERT statement. It does not instantiate any models nor does it trigger Active Record callbacks or validations. Though passed values go through Active Record’s type casting and serialization.

See insert_all for documentation.

Inserts a single record into the database in a single SQL INSERT statement. It does not instantiate any models nor does it trigger Active Record callbacks or validations. Though passed values go through Active Record’s type casting and serialization.

See insert_all! for more.

Inserts multiple records into the database in a single SQL INSERT statement. It does not instantiate any models nor does it trigger Active Record callbacks or validations. Though passed values go through Active Record’s type casting and serialization.

The attributes parameter is an Array of Hashes. Every Hash determines the attributes for a single row and must have the same keys.

Rows are considered to be unique by every unique index on the table. Any duplicate rows are skipped. Override with :unique_by (see below).

Returns an ActiveRecord::Result with its contents based on :returning (see below).

Options

:returning

(PostgreSQL, SQLite3, and MariaDB only) An array of attributes to return for all successfully inserted records, which by default is the primary key. Pass returning: %w[ id name ] for both id and name or returning: false to omit the underlying RETURNING SQL clause entirely.

You can also pass an SQL string if you need more control on the return values (for example, returning: Arel.sql("id, name as new_name")).

:unique_by

(PostgreSQL and SQLite only) By default rows are considered to be unique by every unique index on the table. Any duplicate rows are skipped.

To skip rows according to just one unique index pass :unique_by.

Consider a Book model where no duplicate ISBNs make sense, but if any row has an existing id, or is not unique by another unique index, ActiveRecord::RecordNotUnique is raised.

Unique indexes can be identified by columns or name:

unique_by: :isbn
unique_by: %i[ author_id name ]
unique_by: :index_books_on_isbn

:record_timestamps

By default, automatic setting of timestamp columns is controlled by the model’s record_timestamps config, matching typical behavior.

To override this and force automatic setting of timestamp columns one way or the other, pass :record_timestamps:

record_timestamps: true  # Always set timestamps automatically
record_timestamps: false # Never set timestamps automatically

Because it relies on the index information from the database :unique_by is recommended to be paired with Active Record’s schema_cache.

Example

# Insert records and skip inserting any duplicates.
# Here "Eloquent Ruby" is skipped because its id is not unique.

Book.insert_all([
  { id: 1, title: "Rework", author: "David" },
  { id: 1, title: "Eloquent Ruby", author: "Russ" }
])

# insert_all works on chained scopes, and you can use create_with
# to set default attributes for all inserted records.

author.books.create_with(created_at: Time.now).insert_all([
  { id: 1, title: "Rework" },
  { id: 2, title: "Eloquent Ruby" }
])

Inserts multiple records into the database in a single SQL INSERT statement. It does not instantiate any models nor does it trigger Active Record callbacks or validations. Though passed values go through Active Record’s type casting and serialization.

The attributes parameter is an Array of Hashes. Every Hash determines the attributes for a single row and must have the same keys.

Raises ActiveRecord::RecordNotUnique if any rows violate a unique index on the table. In that case, no rows are inserted.

To skip duplicate rows, see insert_all. To replace them, see upsert_all.

Returns an ActiveRecord::Result with its contents based on :returning (see below).

Options

:returning

(PostgreSQL, SQLite3, and MariaDB only) An array of attributes to return for all successfully inserted records, which by default is the primary key. Pass returning: %w[ id name ] for both id and name or returning: false to omit the underlying RETURNING SQL clause entirely.

You can also pass an SQL string if you need more control on the return values (for example, returning: Arel.sql("id, name as new_name")).

:record_timestamps

By default, automatic setting of timestamp columns is controlled by the model’s record_timestamps config, matching typical behavior.

To override this and force automatic setting of timestamp columns one way or the other, pass :record_timestamps:

record_timestamps: true  # Always set timestamps automatically
record_timestamps: false # Never set timestamps automatically

Examples

# Insert multiple records
Book.insert_all!([
  { title: "Rework", author: "David" },
  { title: "Eloquent Ruby", author: "Russ" }
])

# Raises ActiveRecord::RecordNotUnique because "Eloquent Ruby"
# does not have a unique id.
Book.insert_all!([
  { id: 1, title: "Rework", author: "David" },
  { id: 1, title: "Eloquent Ruby", author: "Russ" }
])

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] }

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>

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

Returns true if there is more than one record.

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

Returns true if there are no records.

When a pattern argument is given, this method checks whether elements in the Enumerable match the pattern via the case-equality operator (===).

posts.none?(Comment) # => true or false

Returns true if there is exactly one record.

When a pattern argument is given, this method checks whether elements in the Enumerable match the pattern via the case-equality operator (===).

posts.one?(Post) # => true or false

Forces reloading of relation.

Returns true if the relation was scheduled on the background thread pool.

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.

Returns size of the records.

Converts relation objects to Array.

Returns sql statement for the relation.

User.where(name: 'Oscar').to_sql
# SELECT "users".* FROM "users"  WHERE "users"."name" = 'Oscar'

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'"

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. Any strings provided will be type cast, unless you use Arel.sql. (Don’t pass user-provided values to Arel.sql.)

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')

# Update all books with 'Rails' in their title
Book.where('title LIKE ?', '%Rails%').update_all(title: Arel.sql("title + ' - volume 1'"))

Updates the counters of the records in the current relation.

Parameters

• counter - A Hash 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)

Updates or inserts (upserts) a single record into the database in a single SQL INSERT statement. It does not instantiate any models nor does it trigger Active Record callbacks or validations. Though passed values go through Active Record’s type casting and serialization.

See upsert_all for documentation.

Updates or inserts (upserts) multiple records into the database in a single SQL INSERT statement. It does not instantiate any models nor does it trigger Active Record callbacks or validations. Though passed values go through Active Record’s type casting and serialization.

The attributes parameter is an Array of Hashes. Every Hash determines the attributes for a single row and must have the same keys.

Returns an ActiveRecord::Result with its contents based on :returning (see below).

By default, upsert_all will update all the columns that can be updated when there is a conflict. These are all the columns except primary keys, read-only columns, and columns covered by the optional unique_by.

Options

:returning

(PostgreSQL, SQLite3, and MariaDB only) An array of attributes to return for all successfully inserted records, which by default is the primary key. Pass returning: %w[ id name ] for both id and name or returning: false to omit the underlying RETURNING SQL clause entirely.

You can also pass an SQL string if you need more control on the return values (for example, returning: Arel.sql("id, name as new_name")).

:unique_by

(PostgreSQL and SQLite only) By default rows are considered to be unique by every unique index on the table. Any duplicate rows are skipped.

To skip rows according to just one unique index pass :unique_by.

Consider a Book model where no duplicate ISBNs make sense, but if any row has an existing id, or is not unique by another unique index, ActiveRecord::RecordNotUnique is raised.

Unique indexes can be identified by columns or name:

unique_by: :isbn
unique_by: %i[ author_id name ]
unique_by: :index_books_on_isbn

Because it relies on the index information from the database :unique_by is recommended to be paired with Active Record’s schema_cache.

:on_duplicate

Configure the SQL update sentence that will be used in case of conflict.

NOTE: If you use this option you must provide all the columns you want to update by yourself.

Example:

Commodity.upsert_all(
  [
    { id: 2, name: "Copper", price: 4.84 },
    { id: 4, name: "Gold", price: 1380.87 },
    { id: 6, name: "Aluminium", price: 0.35 }
  ],
  on_duplicate: Arel.sql("price = GREATEST(commodities.price, EXCLUDED.price)")
)

See the related :update_only option. Both options can’t be used at the same time.

:update_only

Provide a list of column names that will be updated in case of conflict. If not provided, upsert_all will update all the columns that can be updated. These are all the columns except primary keys, read-only columns, and columns covered by the optional unique_by

Example:

Commodity.upsert_all(
  [
    { id: 2, name: "Copper", price: 4.84 },
    { id: 4, name: "Gold", price: 1380.87 },
    { id: 6, name: "Aluminium", price: 0.35 }
  ],
  update_only: [:price] # Only prices will be updated
)

See the related :on_duplicate option. Both options can’t be used at the same time.

:record_timestamps

By default, automatic setting of timestamp columns is controlled by the model’s record_timestamps config, matching typical behavior.

To override this and force automatic setting of timestamp columns one way or the other, pass :record_timestamps:

record_timestamps: true  # Always set timestamps automatically
record_timestamps: false # Never set timestamps automatically

Examples

# Inserts multiple records, performing an upsert when records have duplicate ISBNs.
# Here "Eloquent Ruby" overwrites "Rework" because its ISBN is duplicate.

Book.upsert_all([
  { title: "Rework", author: "David", isbn: "1" },
  { title: "Eloquent Ruby", author: "Russ", isbn: "1" }
], unique_by: :isbn)

Book.find_by(isbn: "1").title # => "Eloquent Ruby"