module ActiveRecord::ConnectionAdapters::DatabaseStatements
Public Class Methods
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 5 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 273 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 282 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 296 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 301 def commit_db_transaction() end
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 315 def default_sequence_name(table, column) nil end
Executes the delete statement and returns the number of rows affected.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 160 def delete(arel, name = nil, binds = []) sql, binds = to_sql_and_binds(arel, binds) exec_delete(sql, name, binds) end
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 387 def empty_insert_statement_value "DEFAULT VALUES" 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 122 def exec_delete(sql, name = nil, 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 114 def exec_insert(sql, name = nil, binds = [], pk = nil, sequence_name = nil) sql, binds = sql_for_insert(sql, pk, nil, sequence_name, binds) 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 107 def exec_query(sql, name = "SQL", binds = [], prepare: false) raise NotImplementedError 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 134 def exec_update(sql, name = nil, binds = []) exec_query(sql, name, binds) end
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.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 100 def execute(sql, name = nil) raise NotImplementedError end
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
.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 146 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
Inserts the given fixture into the table. Overridden in adapters that require something beyond a simple insert (eg. Oracle). Most of adapters should implement `insert_fixtures` that leverages bulk SQL insert. We keep this method to provide fallback for databases like sqlite that do not support bulk inserts.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 329 def insert_fixture(fixture, table_name) fixture = fixture.stringify_keys columns = schema_cache.columns_hash(table_name) binds = fixture.map do |name, value| if column = columns[name] type = lookup_cast_type_from_column(column) Relation::QueryAttribute.new(name, value, type) else raise Fixture::FixtureError, %(table "#{table_name}" has no column named #{name.inspect}.) end end table = Arel::Table.new(table_name) values = binds.map do |bind| value = with_yaml_fallback(bind.value_for_database) [table[bind.name], value] end manager = Arel::InsertManager.new manager.into(table) manager.insert(values) execute manager.to_sql, "Fixture Insert" end
Inserts a set of fixtures into the table. Overridden in adapters that require something beyond a simple insert (eg. Oracle).
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 357 def insert_fixtures(fixtures, table_name) ActiveSupport::Deprecation.warn(<<-MSG.squish) `insert_fixtures` is deprecated and will be removed in the next version of Rails. Consider using `insert_fixtures_set` for performance improvement. MSG return if fixtures.empty? execute(build_fixture_sql(fixtures, table_name), "Fixtures Insert") end
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 367 def insert_fixtures_set(fixture_set, tables_to_delete = []) fixture_inserts = fixture_set.map do |table_name, fixtures| next if fixtures.empty? build_fixture_sql(fixtures, table_name) end.compact table_deletes = tables_to_delete.map { |table| "DELETE FROM #{quote_table_name table}".dup } total_sql = Array.wrap(combine_multi_statements(table_deletes + fixture_inserts)) disable_referential_integrity do transaction(requires_new: true) do total_sql.each do |sql| execute sql, "Fixtures Load" yield if block_given? end end end end
Set the sequence to the max value of the table's column.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 320 def reset_sequence!(table, column, sequence = nil) # Do nothing by default. Implement for PostgreSQL, Oracle, ... 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 305 def rollback_db_transaction exec_rollback_db_transaction end
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 311 def rollback_to_savepoint(name = nil) exec_rollback_to_savepoint(name) end
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.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 397 def sanitize_limit(limit) if limit.is_a?(Integer) || limit.is_a?(Arel::Nodes::SqlLiteral) limit else Integer(limit) end end
Returns an ActiveRecord::Result instance.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 45 def select_all(arel, name = nil, binds = [], preparable: nil) arel = arel_from_relation(arel) sql, binds = to_sql_and_binds(arel, binds) if !prepared_statements || (arel.is_a?(String) && preparable.nil?) preparable = false else preparable = visitor.preparable end if prepared_statements && preparable select_prepared(sql, name, binds) else select(sql, name, binds) end 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 62 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 79 def select_rows(arel, name = nil, binds = []) select_all(arel, name, binds).rows end
Returns a single value from a record
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 67 def select_value(arel, name = nil, binds = []) single_value_from_rows(select_rows(arel, name, binds)) 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 73 def select_values(arel, name = nil, binds = []) select_rows(arel, name, binds).map(&:first) end
Converts an arel AST to SQL
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 11 def to_sql(arel_or_sql_string, binds = []) sql, _ = to_sql_and_binds(arel_or_sql_string, binds) sql 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/5.7/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 mysql2 and postgresql adapters support setting the transaction isolation level.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 246 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
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 284 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 263 def transaction_open? current_transaction.open? end
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 277 def transaction_state current_transaction.state end
Executes the truncate statement.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 127 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 154 def update(arel, name = nil, binds = []) sql, binds = to_sql_and_binds(arel, binds) exec_update(sql, name, binds) end
Private Instance Methods
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 484 def arel_from_relation(relation) if relation.is_a?(Relation) relation.arel else relation end end
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 420 def build_fixture_sql(fixtures, table_name) columns = schema_cache.columns_hash(table_name) values = fixtures.map do |fixture| fixture = fixture.stringify_keys unknown_columns = fixture.keys - columns.keys if unknown_columns.any? raise Fixture::FixtureError, %(table "#{table_name}" has no columns named #{unknown_columns.map(&:inspect).join(', ')}.) end columns.map do |name, column| if fixture.key?(name) type = lookup_cast_type_from_column(column) bind = Relation::QueryAttribute.new(name, fixture[name], type) with_yaml_fallback(bind.value_for_database) else default_insert_value(column) end end end table = Arel::Table.new(table_name) manager = Arel::InsertManager.new manager.into(table) columns.each_key { |column| manager.columns << table[column] } manager.values = manager.create_values_list(values) manager.to_sql end
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 451 def combine_multi_statements(total_sql) total_sql.join(";\n") end
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 416 def default_insert_value(column) Arel.sql("DEFAULT") end
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 475 def last_inserted_id(result) single_value_from_rows(result.rows) end
Returns an ActiveRecord::Result instance.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 463 def select(sql, name = nil, binds = []) exec_query(sql, name, binds, prepare: false) end
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 467 def select_prepared(sql, name = nil, binds = []) exec_query(sql, name, binds, prepare: true) end
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 479 def single_value_from_rows(rows) row = rows.first row && row.first end
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 471 def sql_for_insert(sql, pk, id_value, sequence_name, binds) [sql, binds] end
Returns a subquery for the given key using the join information.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 456 def subquery_for(key, select) subselect = select.clone subselect.projections = [key] subselect end
Fixture value is quoted by Arel, however scalar values are not quotable. In this case we want to convert the column value to YAML.
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 495 def with_yaml_fallback(value) if value.is_a?(Hash) || value.is_a?(Array) YAML.dump(value) else value end end