module ActiveRecord::ConnectionAdapters::DatabaseStatements
Public Class Methods
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 6 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 activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 274 def add_transaction_record(record) current_transaction.add_record(record) end
Begins the transaction (and turns off auto-committing).
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 283 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 activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 297 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 activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 302 def commit_db_transaction() end
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 316 def default_sequence_name(table, column) nil end
Executes the delete statement and returns the number of rows affected.
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 161 def delete(arel, name = nil, binds = []) sql, binds = to_sql_and_binds(arel, binds) exec_delete(sql, name, binds) end
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 390 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 activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 123 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 activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 115 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 activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 108 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 activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 135 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 activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 101 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 activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 147 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 activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 330 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 activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 358 def insert_fixtures(fixtures, table_name) return if fixtures.empty? 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 Arel.sql("DEFAULT") 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) execute manager.to_sql, "Fixtures Insert" end
Set the sequence to the max value of the table's column.
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 321 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 activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 306 def rollback_db_transaction exec_rollback_db_transaction end
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 312 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 activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 400 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 activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 46 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 activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 63 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 activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 80 def select_rows(arel, name = nil, binds = []) select_all(arel, name, binds).rows end
Returns a single value from a record
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 68 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 activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 74 def select_values(arel, name = nil, binds = []) select_rows(arel, name, binds).map(&:first) end
Converts an arel AST to SQL
# 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
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 activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 247 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 activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 285 def transaction_isolation_levels { read_uncommitted: "READ UNCOMMITTED", read_committed: "READ COMMITTED", repeatable_read: "REPEATABLE READ", serializable: "SERIALIZABLE" } end
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 264 def transaction_open? current_transaction.open? end
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 278 def transaction_state current_transaction.state end
Executes the truncate statement.
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 128 def truncate(table_name, name = nil) raise NotImplementedError end
Executes the update statement and returns the number of rows affected.
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 155 def update(arel, name = nil, binds = []) sql, binds = to_sql_and_binds(arel, binds) exec_update(sql, name, binds) end
Private Instance Methods
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 449 def arel_from_relation(relation) if relation.is_a?(Relation) relation.arel else relation end end
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 440 def last_inserted_id(result) single_value_from_rows(result.rows) end
Returns an ActiveRecord::Result
instance.
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 428 def select(sql, name = nil, binds = []) exec_query(sql, name, binds, prepare: false) end
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 432 def select_prepared(sql, name = nil, binds = []) exec_query(sql, name, binds, prepare: true) end
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 444 def single_value_from_rows(rows) row = rows.first row && row.first end
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 436 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 activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 421 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 activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 460 def with_yaml_fallback(value) if value.is_a?(Hash) || value.is_a?(Array) YAML.dump(value) else value end end