module ActiveRecord::ConnectionAdapters::DatabaseStatements

Public Class Methods

Calls superclass method

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 4
def initialize
  super
  reset_transaction
end

Public Instance Methods

add_transaction_record(record) Show source

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 248
def add_transaction_record(record)
  @transaction.add_record(record)
end

begin_db_transaction() Show source

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

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 253
def begin_db_transaction()    end

begin_isolated_db_transaction(isolation) Show 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 activerecord/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() Show source

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

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 272
def commit_db_transaction()   end

default_sequence_name(table, column) Show source

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 278
def default_sequence_name(table, column)
  nil
end

delete(arel, name = nil, binds = []) Show source

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

# File activerecord/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() Show source

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 301
def empty_insert_statement_value
  "DEFAULT VALUES"
end

exec_delete(sql, name, binds) Show 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 activerecord/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) Show 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 activerecord/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 = []) Show 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 activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 61
def exec_query(sql, name = 'SQL', binds = [])
end

exec_update(sql, name, binds) Show 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 activerecord/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) Show source

Executes the SQL statement in the context of this connection.

# File activerecord/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 = []) Show 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 activerecord/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) Show source

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 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) Show source

# File activerecord/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) Show source

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

# File activerecord/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() Show source

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 276
def rollback_db_transaction() end

sanitize_limit(limit) Show 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 activerecord/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 = []) Show source

Returns an ActiveRecord::Result instance.

# File activerecord/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 = []) Show source

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 29
def select_one(arel, name = nil, binds = [])
  select_all(arel, name, binds).first
end

select_rows(sql, name = nil, binds = []) Show source

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 49
def select_rows(sql, name = nil, binds = [])
end

select_value(arel, name = nil, binds = []) Show source

Returns a single value from a record

# File activerecord/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) Show 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 activerecord/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?() Show source

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

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 111
def supports_statement_cache?
  false
end

to_sql(arel, binds = []) Show source

Converts an arel AST to SQL

# File activerecord/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 = {}) { || ... } Show 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 activerecord/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() Show source

# File activerecord/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?() Show source

# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 226
def transaction_open?
  @transaction.open?
end

update(arel, name = nil, binds = []) Show source

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

# File activerecord/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) Show source

# File activerecord/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) Show source

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

# File activerecord/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) Show source

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

# File activerecord/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) Show source

# File activerecord/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 = []) Show source

Returns an ActiveRecord::Result instance.

# File activerecord/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) Show source

# File activerecord/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) Show source

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

# File activerecord/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) Show source