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Register a record with the current transaction so that its after_commit and after_rollback callbacks can be called.
Begins the transaction (and turns off auto-committing).
Begins the transaction with the isolation level set. Raises an error by default; adapters that support setting the isolation level should implement this method.
Commits the transaction (and turns on auto-committing).
Executes the delete statement and returns the number of rows affected.
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.
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.
Executes sql statement in the context of this connection using
binds as the bind substitutes. name is logged
along with the executed sql statement.
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.
Executes the SQL statement in the context of this connection.
Returns the last auto-generated ID from the affected table.
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.
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 106 def insert(arel, name = nil, pk = nil, id_value = nil, sequence_name = nil, binds = []) sql, binds = sql_for_insert(to_sql(arel, binds), pk, id_value, sequence_name, binds) value = exec_insert(sql, name, binds, pk, sequence_name) id_value || last_inserted_id(value) end
Inserts the given fixture into the table. Overridden in adapters that require something beyond a simple insert (eg. Oracle).
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 274 def insert_fixture(fixture, table_name) columns = schema_cache.columns_hash(table_name) key_list = [] value_list = fixture.map do |name, value| key_list << quote_column_name(name) quote(value, columns[name]) end execute "INSERT INTO #{quote_table_name(table_name)} (#{key_list.join(', ')}) VALUES (#{value_list.join(', ')})", 'Fixture Insert' end
Set the sequence to the max value of the table's column.
Rolls back the transaction (and turns on auto-committing). Must be done if the transaction block raises an exception or returns false.
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 a comma-delimited list of
integers, or an Arel SQL literal.
Returns Integer and Arel::Nodes::SqlLiteral limits as is. Returns the sanitized limit parameter, either as an integer, or as a string which contains a comma-delimited list of integers.
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 299 def sanitize_limit(limit) if limit.is_a?(Integer) || limit.is_a?(Arel::Nodes::SqlLiteral) limit elsif limit.to_s.include?(',') Arel.sql limit.to_s.split(',').map{ |i| Integer(i) }.join(',') else Integer(limit) end end
Returns an ActiveRecord::Result instance.
Returns a record hash with the column names as keys and column values as values.
Returns an array of arrays containing the field values. Order is the same
as that returned by columns.
Returns a single value from a record
Returns an array of the values of the first column in a select:
select_values("SELECT id FROM companies LIMIT 3") => [1,2,3]Returns true when the connection adapter supports prepared
statement caching, otherwise returns false
Converts an arel AST to SQL
Runs the given block in a database transaction, and returns the result of the block.
Nested transactions support
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/5.0/en/savepoint.html Savepoints are supported by MySQL and PostgreSQL. SQLite3 version >= '3.6.8' supports savepoints.
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_newis set, the block will be wrapped in a database savepoint acting as a sub-transaction.
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!
endTransaction 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 mysql, mysql2 and postgresql adapters support setting the transaction isolation level. However, support is disabled for MySQL versions below 5, because they are affected by a bug which means the isolation level gets persisted outside the transaction.
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 204 def transaction(options = {}) options.assert_valid_keys :requires_new, :joinable, :isolation if !options[:requires_new] && current_transaction.joinable? if options[:isolation] raise ActiveRecord::TransactionIsolationError, "cannot set isolation when joining a transaction" end yield else transaction_manager.within_new_transaction(options) { yield } end rescue ActiveRecord::Rollback # rollbacks are silently swallowed end
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 240 def transaction_isolation_levels { read_uncommitted: "READ UNCOMMITTED", read_committed: "READ COMMITTED", repeatable_read: "REPEATABLE READ", serializable: "SERIALIZABLE" } end
Executes the truncate statement.
Executes the update statement and returns the number of rows affected.
Executes the delete statement and returns the number of rows affected.
Returns the last auto-generated ID from the affected table.
Returns an ActiveRecord::Result instance.
Returns a subquery for the given key using the join information.