module ActiveRecord::ConnectionAdapters::DatabaseStatements

Public Class Methods

new() click to toggle source
Calls superclass method
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 4
def initialize
  super
  reset_transaction
end

Public Instance Methods

add_transaction_record(record) click to toggle source

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 248
def add_transaction_record(record)
  @transaction.add_record(record)
end
begin_db_transaction() click to toggle source

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

# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 253
def begin_db_transaction()    end
begin_isolated_db_transaction(isolation) click to toggle source

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 267
def begin_isolated_db_transaction(isolation)
  raise ActiveRecord::TransactionIsolationError, "adapter does not support setting transaction isolation"
end
commit_db_transaction() click to toggle source

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

# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 272
def commit_db_transaction()   end
default_sequence_name(table, column) click to toggle source
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 278
def default_sequence_name(table, column)
  nil
end
delete(arel, name = nil, binds = []) click to toggle source

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

# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 105
def delete(arel, name = nil, binds = [])
  exec_delete(to_sql(arel, binds), name, binds)
end
empty_insert_statement_value() click to toggle source
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 301
def empty_insert_statement_value
  "DEFAULT VALUES"
end
exec_delete(sql, name, binds) click to toggle source

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 74
def exec_delete(sql, name, binds)
  exec_query(sql, name, binds)
end
exec_insert(sql, name, binds, pk = nil, sequence_name = nil) click to toggle source

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 67
def exec_insert(sql, name, binds, pk = nil, sequence_name = nil)
  exec_query(sql, name, binds)
end
exec_query(sql, name = 'SQL', binds = []) click to toggle source

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 61
def exec_query(sql, name = 'SQL', binds = [])
end
exec_update(sql, name, binds) click to toggle source

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 81
def exec_update(sql, name, binds)
  exec_query(sql, name, binds)
end
execute(sql, name = nil) click to toggle source

Executes the SQL statement in the context of this connection.

# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 54
def execute(sql, name = nil)
end
insert(arel, name = nil, pk = nil, id_value = nil, sequence_name = nil, binds = []) click to toggle source

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 93
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
insert_fixture(fixture, table_name) click to toggle source

Inserts the given fixture 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 289
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
limited_update_conditions(where_sql, quoted_table_name, quoted_primary_key) click to toggle source
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 305
def limited_update_conditions(where_sql, quoted_table_name, quoted_primary_key)
  "WHERE #{quoted_primary_key} IN (SELECT #{quoted_primary_key} FROM #{quoted_table_name} #{where_sql})"
end
reset_sequence!(table, column, sequence = nil) click to toggle source

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

# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 283
def reset_sequence!(table, column, sequence = nil)
  # Do nothing by default. Implement for PostgreSQL, Oracle, ...
end
rollback_db_transaction() click to toggle source

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 276
def rollback_db_transaction() end
sanitize_limit(limit) click to toggle source

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 lib/active_record/connection_adapters/abstract/database_statements.rb, line 318
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
select_all(arel, name = nil, binds = []) click to toggle source

Returns an ActiveRecord::Result instance.

# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 22
def select_all(arel, name = nil, binds = [])
  arel, binds = binds_from_relation arel, binds
  select(to_sql(arel, binds), name, binds)
end
select_one(arel, name = nil, binds = []) click to toggle source

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 29
def select_one(arel, name = nil, binds = [])
  select_all(arel, name, binds).first
end
select_rows(sql, name = nil, binds = []) click to toggle source

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 49
def select_rows(sql, name = nil, binds = [])
end
select_value(arel, name = nil, binds = []) click to toggle source

Returns a single value from a record

# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 34
def select_value(arel, name = nil, binds = [])
  if result = select_one(arel, name, binds)
    result.values.first
  end
end
select_values(arel, name = nil) click to toggle source

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 42
def select_values(arel, name = nil)
  arel, binds = binds_from_relation arel, []
  select_rows(to_sql(arel, binds), name, binds).map(&:first)
end
supports_statement_cache?() click to toggle source

Returns true when the connection adapter supports prepared statement caching, otherwise returns false

# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 111
def supports_statement_cache?
  false
end
to_sql(arel, binds = []) click to toggle source

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)
    binds = binds.dup
    visitor.accept(arel.ast) do
      quote(*binds.shift.reverse)
    end
  else
    arel
  end
end
transaction(options = {}) { || ... } click to toggle source

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 191
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
    within_new_transaction(options) { yield }
  end
rescue ActiveRecord::Rollback
  # rollbacks are silently swallowed
end
transaction_isolation_levels() click to toggle source
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 255
def transaction_isolation_levels
  {
    read_uncommitted: "READ UNCOMMITTED",
    read_committed:   "READ COMMITTED",
    repeatable_read:  "REPEATABLE READ",
    serializable:     "SERIALIZABLE"
  }
end
transaction_open?() click to toggle source
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 226
def transaction_open?
  @transaction.open?
end
update(arel, name = nil, binds = []) click to toggle source

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

# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 100
def update(arel, name = nil, binds = [])
  exec_update(to_sql(arel, binds), name, binds)
end

Protected Instance Methods

binds_from_relation(relation, binds) click to toggle source
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 383
def binds_from_relation(relation, binds)
  if relation.is_a?(Relation) && binds.blank?
    relation, binds = relation.arel, relation.bind_values
  end
  [relation, binds]
end
delete_sql(sql, name = nil) click to toggle source

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

# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 370
def delete_sql(sql, name = nil)
  update_sql(sql, name)
end
insert_sql(sql, name = nil, pk = nil, id_value = nil, sequence_name = nil) click to toggle source

Returns the last auto-generated ID from the affected table.

# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 359
def insert_sql(sql, name = nil, pk = nil, id_value = nil, sequence_name = nil)
  execute(sql, name)
  id_value
end
last_inserted_id(result) click to toggle source
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 378
def last_inserted_id(result)
  row = result.rows.first
  row && row.first
end
select(sql, name = nil, binds = []) click to toggle source

Returns an ActiveRecord::Result instance.

# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 354
def select(sql, name = nil, binds = [])
end
sql_for_insert(sql, pk, id_value, sequence_name, binds) click to toggle source
# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 374
def sql_for_insert(sql, pk, id_value, sequence_name, binds)
  [sql, binds]
end
subquery_for(key, select) click to toggle source

Returns a subquery for the given key using the join information.

# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 347
def subquery_for(key, select)
  subselect = select.clone
  subselect.projections = [key]
  subselect
end
update_sql(sql, name = nil) click to toggle source

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

# File lib/active_record/connection_adapters/abstract/database_statements.rb, line 365
def update_sql(sql, name = nil)
  execute(sql, name)
end