ActiveRecord::ConnectionAdapters::DatabaseStatements

new()

📝 Source code

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 6
      def initialize
        super
        reset_transaction
      end

🔎 See on GitHub

add_transaction_record(record, ensure_finalize = true)

Register a record with the current transaction so that its after_commit and after_rollback callbacks can be called.

📝 Source code

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 349
      def add_transaction_record(record, ensure_finalize = true)
        current_transaction.add_record(record, ensure_finalize)
      end

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begin_db_transaction()

Begins the transaction (and turns off auto-committing).

📝 Source code

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 354
      def begin_db_transaction()    end

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begin_isolated_db_transaction(isolation)

Begins the transaction with the isolation level set. Raises an error by default; adapters that support setting the isolation level should implement this method.

📝 Source code

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 368
      def begin_isolated_db_transaction(isolation)
        raise ActiveRecord::TransactionIsolationError, "adapter does not support setting transaction isolation"
      end

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commit_db_transaction()

Commits the transaction (and turns on auto-committing).

📝 Source code

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 373
      def commit_db_transaction()   end

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create(arel, name = nil, pk = nil, id_value = nil, sequence_name = nil, binds = [])

Alias for: insert

default_sequence_name(table, column)

📝 Source code

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 387
      def default_sequence_name(table, column)
        nil
      end

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delete(arel, name = nil, binds = [])

Executes the delete statement and returns the number of rows affected.

📝 Source code

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 183
      def delete(arel, name = nil, binds = [])
        sql, binds = to_sql_and_binds(arel, binds)
        exec_delete(sql, name, binds)
      end

🔎 See on GitHub

empty_insert_statement_value(primary_key = nil)

📝 Source code

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 419
      def empty_insert_statement_value(primary_key = nil)
        "DEFAULT VALUES"
      end

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exec_delete(sql, name = nil, binds = [])

Executes delete sql statement in the context of this connection using binds as the bind substitutes. name is logged along with the executed sql statement.

📝 Source code

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 142
      def exec_delete(sql, name = nil, binds = [])
        exec_query(sql, name, binds)
      end

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exec_insert(sql, name = nil, binds = [], pk = nil, sequence_name = nil)

Executes insert sql statement in the context of this connection using binds as the bind substitutes. name is logged along with the executed sql statement.

📝 Source code

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 134
      def exec_insert(sql, name = nil, binds = [], pk = nil, sequence_name = nil)
        sql, binds = sql_for_insert(sql, pk, binds)
        exec_query(sql, name, binds)
      end

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exec_query(sql, name = "SQL", binds = [], prepare: false)

Executes sql statement in the context of this connection using binds as the bind substitutes. name is logged along with the executed sql statement.

📝 Source code

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 127
      def exec_query(sql, name = "SQL", binds = [], prepare: false)
        raise NotImplementedError
      end

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exec_update(sql, name = nil, binds = [])

Executes update sql statement in the context of this connection using binds as the bind substitutes. name is logged along with the executed sql statement.

📝 Source code

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 149
      def exec_update(sql, name = nil, binds = [])
        exec_query(sql, name, binds)
      end

🔎 See on GitHub

execute(sql, name = nil)

Executes the SQL statement in the context of this connection and returns the raw result from the connection adapter. Note: depending on your database connector, the result returned by this method may be manually memory managed. Consider using the exec_query wrapper instead.

📝 Source code

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 120
      def execute(sql, name = nil)
        raise NotImplementedError
      end

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insert(arel, name = nil, pk = nil, id_value = nil, sequence_name = nil, binds = [])

Executes an INSERT query and returns the new record's ID

id_value will be returned unless the value is nil, in which case the database will attempt to calculate the last inserted id and return that value.

If the next id was calculated in advance (as in Oracle), it should be passed in as id_value.

Also aliased as: create

📝 Source code

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 169
      def insert(arel, name = nil, pk = nil, id_value = nil, sequence_name = nil, binds = [])
        sql, binds = to_sql_and_binds(arel, binds)
        value = exec_insert(sql, name, binds, pk, sequence_name)
        id_value || last_inserted_id(value)
      end

🔎 See on GitHub

insert_fixture(fixture, table_name)

Inserts the given fixture into the table. Overridden in adapters that require something beyond a simple insert (e.g. Oracle). Most of adapters should implement insert_fixtures_set that leverages bulk SQL insert. We keep this method to provide fallback for databases like sqlite that do not support bulk inserts.

📝 Source code

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 401
      def insert_fixture(fixture, table_name)
        execute(build_fixture_sql(Array.wrap(fixture), table_name), "Fixture Insert")
      end

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insert_fixtures_set(fixture_set, tables_to_delete = [])

📝 Source code

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 405
      def insert_fixtures_set(fixture_set, tables_to_delete = [])
        fixture_inserts = build_fixture_statements(fixture_set)
        table_deletes = tables_to_delete.map { |table| "DELETE FROM #{quote_table_name(table)}" }
        statements = table_deletes + fixture_inserts

        with_multi_statements do
          disable_referential_integrity do
            transaction(requires_new: true) do
              execute_batch(statements, "Fixtures Load")
            end
          end
        end
      end

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reset_sequence!(table, column, sequence = nil)

Set the sequence to the max value of the table's column.

📝 Source code

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 392
      def reset_sequence!(table, column, sequence = nil)
        # Do nothing by default. Implement for PostgreSQL, Oracle, ...
      end

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rollback_db_transaction()

Rolls back the transaction (and turns on auto-committing). Must be done if the transaction block raises an exception or returns false.

📝 Source code

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 377
      def rollback_db_transaction
        exec_rollback_db_transaction
      end

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rollback_to_savepoint(name = nil)

📝 Source code

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 383
      def rollback_to_savepoint(name = nil)
        exec_rollback_to_savepoint(name)
      end

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sanitize_limit(limit)

Sanitizes the given LIMIT parameter in order to prevent SQL injection.

The limit may be anything that can evaluate to a string via to_s. It should look like an integer, or an Arel SQL literal.

Returns Integer and Arel::Nodes::SqlLiteral limits as is.

📝 Source code

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 429
      def sanitize_limit(limit)
        if limit.is_a?(Integer) || limit.is_a?(Arel::Nodes::SqlLiteral)
          limit
        else
          Integer(limit)
        end
      end

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select_all(arel, name = nil, binds = [], preparable: nil)

Returns an ActiveRecord::Result instance.

📝 Source code

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 62
      def select_all(arel, name = nil, binds = [], preparable: nil)
        arel = arel_from_relation(arel)
        sql, binds, preparable = to_sql_and_binds(arel, binds, preparable)

        if prepared_statements && preparable
          select_prepared(sql, name, binds)
        else
          select(sql, name, binds)
        end
      rescue ::RangeError
        ActiveRecord::Result.new([], [])
      end

🔎 See on GitHub

select_one(arel, name = nil, binds = [])

Returns a record hash with the column names as keys and column values as values.

📝 Source code

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 77
      def select_one(arel, name = nil, binds = [])
        select_all(arel, name, binds).first
      end

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select_rows(arel, name = nil, binds = [])

Returns an array of arrays containing the field values. Order is the same as that returned by columns.

📝 Source code

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 94
      def select_rows(arel, name = nil, binds = [])
        select_all(arel, name, binds).rows
      end

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select_value(arel, name = nil, binds = [])

Returns a single value from a record

📝 Source code

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 82
      def select_value(arel, name = nil, binds = [])
        single_value_from_rows(select_rows(arel, name, binds))
      end

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select_values(arel, name = nil, binds = [])

Returns an array of the values of the first column in a select:

select_values("SELECT id FROM companies LIMIT 3") => [1,2,3]

📝 Source code

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 88
      def select_values(arel, name = nil, binds = [])
        select_rows(arel, name, binds).map(&:first)
      end

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to_sql(arel_or_sql_string, binds = [])

Converts an arel AST to SQL

📝 Source code

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 12
      def to_sql(arel_or_sql_string, binds = [])
        sql, _ = to_sql_and_binds(arel_or_sql_string, binds)
        sql
      end

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transaction(requires_new: nil, isolation: nil, joinable: true)

Runs the given block in a database transaction, and returns the result of the block.

Nested transactions support

transaction calls can be nested. By default, this makes all database statements in the nested transaction block become part of the parent transaction. For example, the following behavior may be surprising:

ActiveRecord::Base.transaction do
  Post.create(title: 'first')
  ActiveRecord::Base.transaction do
    Post.create(title: 'second')
    raise ActiveRecord::Rollback
  end
end

This creates both “first” and “second” posts. Reason is the ActiveRecord::Rollback exception in the nested block does not issue a ROLLBACK. Since these exceptions are captured in transaction blocks, the parent block does not see it and the real transaction is committed.

Most databases don't support true nested transactions. At the time of writing, the only database that supports true nested transactions that we're aware of, is MS-SQL.

In order to get around this problem, transaction will emulate the effect of nested transactions, by using savepoints: dev.mysql.com/doc/refman/en/savepoint.html.

It is safe to call this method if a database transaction is already open, i.e. if transaction is called within another transaction block. In case of a nested call, transaction will behave as follows:

The block will be run without doing anything. All database statements that happen within the block are effectively appended to the already open database transaction.
However, if :requires_new is set, the block will be wrapped in a database savepoint acting as a sub-transaction.

In order to get a ROLLBACK for the nested transaction you may ask for a real sub-transaction by passing requires_new: true. If anything goes wrong, the database rolls back to the beginning of the sub-transaction without rolling back the parent transaction. If we add it to the previous example:

ActiveRecord::Base.transaction do
  Post.create(title: 'first')
  ActiveRecord::Base.transaction(requires_new: true) do
    Post.create(title: 'second')
    raise ActiveRecord::Rollback
  end
end

only post with title “first” is created.

See ActiveRecord::Transactions to learn more.

Caveats

MySQL doesn't support DDL transactions. If you perform a DDL operation, then any created savepoints will be automatically released. For example, if you've created a savepoint, then you execute a CREATE TABLE statement, then the savepoint that was created will be automatically released.

This means that, on MySQL, you shouldn't execute DDL operations inside a transaction call that you know might create a savepoint. Otherwise, transaction will raise exceptions when it tries to release the already-automatically-released savepoints:

Model.connection.transaction do  # BEGIN
  Model.connection.transaction(requires_new: true) do  # CREATE SAVEPOINT active_record_1
    Model.connection.create_table(...)
    # active_record_1 now automatically released
  end  # RELEASE SAVEPOINT active_record_1  <--- BOOM! database error!
end

Transaction isolation

If your database supports setting the isolation level for a transaction, you can set it like so:

Post.transaction(isolation: :serializable) do
  # ...
end

Valid isolation levels are:

:read_uncommitted
:read_committed
:repeatable_read
:serializable

You should consult the documentation for your database to understand the semantics of these different levels:

An ActiveRecord::TransactionIsolationError will be raised if:

The adapter does not support setting the isolation level
You are joining an existing open transaction
You are creating a nested (savepoint) transaction

The mysql2 and postgresql adapters support setting the transaction isolation level.

📝 Source code

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 313
      def transaction(requires_new: nil, isolation: nil, joinable: true)
        if !requires_new && current_transaction.joinable?
          if isolation
            raise ActiveRecord::TransactionIsolationError, "cannot set isolation when joining a transaction"
          end
          yield
        else
          transaction_manager.within_new_transaction(isolation: isolation, joinable: joinable) { yield }
        end
      rescue ActiveRecord::Rollback
        # rollbacks are silently swallowed
      end

🔎 See on GitHub

transaction_isolation_levels()

📝 Source code

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 356
      def transaction_isolation_levels
        {
          read_uncommitted: "READ UNCOMMITTED",
          read_committed:   "READ COMMITTED",
          repeatable_read:  "REPEATABLE READ",
          serializable:     "SERIALIZABLE"
        }
      end

🔎 See on GitHub

transaction_open?()

📝 Source code

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 339
      def transaction_open?
        current_transaction.open?
      end

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truncate(table_name, name = nil)

Executes the truncate statement.

📝 Source code

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 189
      def truncate(table_name, name = nil)
        execute(build_truncate_statement(table_name), name)
      end

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update(arel, name = nil, binds = [])

Executes the update statement and returns the number of rows affected.

📝 Source code

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 177
      def update(arel, name = nil, binds = [])
        sql, binds = to_sql_and_binds(arel, binds)
        exec_update(sql, name, binds)
      end

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write_query?(sql)

Determines whether the SQL statement is a write query.

📝 Source code

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 111
      def write_query?(sql)
        raise NotImplementedError
      end

🔎 See on GitHub

ActiveRecord::ConnectionAdapters::DatabaseStatements

Methods

Class Public methods

new()

Instance Public methods

add_transaction_record(record, ensure_finalize = true)

begin_db_transaction()

begin_isolated_db_transaction(isolation)

commit_db_transaction()

create(arel, name = nil, pk = nil, id_value = nil, sequence_name = nil, binds = [])

default_sequence_name(table, column)

delete(arel, name = nil, binds = [])

empty_insert_statement_value(primary_key = nil)

exec_delete(sql, name = nil, binds = [])

exec_insert(sql, name = nil, binds = [], pk = nil, sequence_name = nil)

exec_query(sql, name = "SQL", binds = [], prepare: false)

exec_update(sql, name = nil, binds = [])

execute(sql, name = nil)

insert(arel, name = nil, pk = nil, id_value = nil, sequence_name = nil, binds = [])

insert_fixture(fixture, table_name)

insert_fixtures_set(fixture_set, tables_to_delete = [])

reset_sequence!(table, column, sequence = nil)

rollback_db_transaction()

rollback_to_savepoint(name = nil)

sanitize_limit(limit)

select_all(arel, name = nil, binds = [], preparable: nil)

select_one(arel, name = nil, binds = [])

select_rows(arel, name = nil, binds = [])

select_value(arel, name = nil, binds = [])

select_values(arel, name = nil, binds = [])

to_sql(arel_or_sql_string, binds = [])

transaction(requires_new: nil, isolation: nil, joinable: true)

Nested transactions support

Caveats

Transaction isolation

transaction_isolation_levels()

transaction_open?()

truncate(table_name, name = nil)

update(arel, name = nil, binds = [])

write_query?(sql)