module ActiveRecord::ConnectionAdapters::DatabaseStatements
Public Class Methods
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 4 def initialize super reset_transaction end
Public Instance Methods
Register a record with the current transaction so that its after_commit and after_rollback callbacks can be called.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 233 def add_transaction_record(record) current_transaction.add_record(record) end
Begins the transaction (and turns off auto-committing).
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 242 def begin_db_transaction() end
Begins the transaction with the isolation level set. Raises an error by default; adapters that support setting the isolation level should implement this method.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 256 def begin_isolated_db_transaction(isolation) raise ActiveRecord::TransactionIsolationError, "adapter does not support setting transaction isolation" end
Commits the transaction (and turns on auto-committing).
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 261 def commit_db_transaction() end
Executes the delete statement and returns the number of rows affected.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 118 def delete(arel, name = nil, binds = []) exec_delete(to_sql(arel, binds), name, binds) end
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.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 82 def exec_delete(sql, name, binds) exec_query(sql, name, binds) end
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.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 75 def exec_insert(sql, name, binds, pk = nil, sequence_name = nil) exec_query(sql, name, binds) end
Executes sql
statement in the context of this connection using
binds
as the bind substitutes. name
is logged
along with the executed sql
statement.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 69 def exec_query(sql, name = 'SQL', binds = []) end
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.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 94 def exec_update(sql, name, binds) exec_query(sql, name, binds) end
Executes the SQL statement in the context of this connection.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 62 def execute(sql, name = nil) end
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 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
Rolls back the transaction (and turns on auto-committing). Must be done if the transaction block raises an exception or returns false.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 265 def rollback_db_transaction exec_rollback_db_transaction end
Returns an ActiveRecord::Result instance.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 30 def select_all(arel, name = nil, binds = []) arel, binds = binds_from_relation arel, binds select(to_sql(arel, binds), name, binds) end
Returns a record hash with the column names as keys and column values as values.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 37 def select_one(arel, name = nil, binds = []) select_all(arel, name, binds).first end
Returns an array of arrays containing the field values. Order is the same
as that returned by columns
.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 57 def select_rows(sql, name = nil, binds = []) end
Returns a single value from a record
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 42 def select_value(arel, name = nil, binds = []) if result = select_one(arel, name, binds) result.values.first end end
Returns an array of the values of the first column in a select:
select_values("SELECT id FROM companies LIMIT 3") => [1,2,3]
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 50 def select_values(arel, name = nil) arel, binds = binds_from_relation arel, [] select_rows(to_sql(arel, binds), name, binds).map(&:first) end
Returns true
when the connection adapter supports prepared
statement caching, otherwise returns false
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 124 def supports_statement_cache? false end
Converts an arel AST to SQL
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 10 def to_sql(arel, binds = []) if arel.respond_to?(:ast) collected = visitor.accept(arel.ast, collector) collected.compile(binds.dup, self) else arel end end
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_new
is 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! 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 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 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 lib/active_record/connection_adapters/abstract/database_statements.rb, line 244 def transaction_isolation_levels { read_uncommitted: "READ UNCOMMITTED", read_committed: "READ COMMITTED", repeatable_read: "REPEATABLE READ", serializable: "SERIALIZABLE" } end
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 223 def transaction_open? current_transaction.open? end
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 237 def transaction_state current_transaction.state end
Executes the truncate statement.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 87 def truncate(table_name, name = nil) raise NotImplementedError end
Executes the update statement and returns the number of rows affected.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 113 def update(arel, name = nil, binds = []) exec_update(to_sql(arel, binds), name, binds) end