Methods
Public Instance methods
add_limit!(sql, options)

Alias for add_limit_offset!.

[ show source ]

     # File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 185
185:       def add_limit!(sql, options)
186:         add_limit_offset!(sql, options) if options
187:       end
add_limit_offset!(sql, options)

Appends LIMIT and OFFSET options to an SQL statement, or some SQL fragment that has the same semantics as LIMIT and OFFSET.

options must be a Hash which contains a +:limit+ option (required) and an +:offset+ option (optional).

This method modifies the sql parameter.

Examples
 add_limit_offset!('SELECT * FROM suppliers', {:limit => 10, :offset => 50})

generates 

 SELECT * FROM suppliers LIMIT 10 OFFSET 50

[ show source ]

     # File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 201
201:       def add_limit_offset!(sql, options)
202:         if limit = options[:limit]
203:           sql << " LIMIT #{sanitize_limit(limit)}"
204:           if offset = options[:offset]
205:             sql << " OFFSET #{offset.to_i}"
206:           end
207:         end
208:         sql
209:       end
add_lock!(sql, options)

Appends a locking clause to an SQL statement. This method modifies the sql parameter. 

  # SELECT * FROM suppliers FOR UPDATE
  add_lock! 'SELECT * FROM suppliers', :lock => true
  add_lock! 'SELECT * FROM suppliers', :lock => ' FOR UPDATE'

[ show source ]

     # File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 216
216:       def add_lock!(sql, options)
217:         case lock = options[:lock]
218:           when true;   sql << ' FOR UPDATE'
219:           when String; sql << " #{lock}"
220:         end
221:       end
begin_db_transaction()

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

[ show source ]

     # File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 175
175:       def begin_db_transaction()    end
case_sensitive_equality_operator()

[ show source ]

     # File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 242
242:       def case_sensitive_equality_operator
243:         "="
244:       end
commit_db_transaction()

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

[ show source ]

     # File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 178
178:       def commit_db_transaction()   end
default_sequence_name(table, column)

[ show source ]

     # File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 223
223:       def default_sequence_name(table, column)
224:         nil
225:       end
delete(sql, name = nil)

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

[ show source ]

    # File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 53
53:       def delete(sql, name = nil)
54:         delete_sql(sql, name)
55:       end
empty_insert_statement(table_name)

[ show source ]

     # File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 238
238:       def empty_insert_statement(table_name)
239:         "INSERT INTO #{quote_table_name(table_name)} VALUES(DEFAULT)"
240:       end
execute(sql, name = nil, skip_logging = false)

Executes the SQL statement in the context of this connection.

[ show source ]

    # File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 38
38:       def execute(sql, name = nil, skip_logging = false)
39:       end
insert(sql, name = nil, pk = nil, id_value = nil, sequence_name = nil)

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

[ show source ]

    # File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 43
43:       def insert(sql, name = nil, pk = nil, id_value = nil, sequence_name = nil)
44:         insert_sql(sql, name, pk, id_value, sequence_name)
45:       end
insert_fixture(fixture, table_name)

Inserts the given fixture into the table. Overridden in adapters that require something beyond a simple insert (eg. Oracle).

[ show source ]

     # File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 234
234:       def insert_fixture(fixture, table_name)
235:         execute "INSERT INTO #{quote_table_name(table_name)} (#{fixture.key_list}) VALUES (#{fixture.value_list})", 'Fixture Insert'
236:       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 246
246:       def limited_update_conditions(where_sql, quoted_table_name, quoted_primary_key)
247:         "WHERE #{quoted_primary_key} IN (SELECT #{quoted_primary_key} FROM #{quoted_table_name} #{where_sql})"
248:       end
outside_transaction?()

Checks whether there is currently no transaction active. This is done by querying the database driver, and does not use the transaction house-keeping information recorded by increment_open_transactions and friends.

Returns true if there is no transaction active, false if there is a transaction active, and nil if this information is unknown.

Not all adapters supports transaction state introspection. Currently, only the PostgreSQL adapter supports this.

[ show source ]

    # File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 67
67:       def outside_transaction?
68:         nil
69:       end
reset_sequence!(table, column, sequence = nil)

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

[ show source ]

     # File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 228
228:       def reset_sequence!(table, column, sequence = nil)
229:         # Do nothing by default.  Implement for PostgreSQL, Oracle, ...
230:       end
rollback_db_transaction()

Rolls back the transaction (and turns on auto-committing). Must be done if the transaction block raises an exception or returns false.

[ show source ]

     # File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 182
182:       def rollback_db_transaction() end
select_all(sql, name = nil)

Returns an array of record hashes with the column names as keys and column values as values.

[ show source ]

   # File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 6
6:       def select_all(sql, name = nil)
7:         select(sql, name)
8:       end
select_one(sql, name = nil)

Returns a record hash with the column names as keys and column values as values.

[ show source ]

    # File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 12
12:       def select_one(sql, name = nil)
13:         result = select_all(sql, name)
14:         result.first if result
15:       end
select_rows(sql, name = nil)

Returns an array of arrays containing the field values. Order is the same as that returned by columns.

[ show source ]

    # File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 33
33:       def select_rows(sql, name = nil)
34:       end
select_value(sql, name = nil)

Returns a single value from a record

[ show source ]

    # File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 18
18:       def select_value(sql, name = nil)
19:         if result = select_one(sql, name)
20:           result.values.first
21:         end
22:       end
select_values(sql, name = nil)

Returns an array of the values of the first column in a select: 

  select_values("SELECT id FROM companies LIMIT 3") => [1,2,3]

[ show source ]

    # File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 26
26:       def select_values(sql, name = nil)
27:         result = select_rows(sql, name)
28:         result.map { |v| v[0] }
29:       end
transaction(options = {}) {|| ...}

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/savepoints.html Savepoints are supported by MySQL and PostgreSQL, but not SQLite3.

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

[ show source ]

     # File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 113
113:       def transaction(options = {})
114:         options.assert_valid_keys :requires_new, :joinable
115: 
116:         last_transaction_joinable = @transaction_joinable
117:         if options.has_key?(:joinable)
118:           @transaction_joinable = options[:joinable]
119:         else
120:           @transaction_joinable = true
121:         end
122:         requires_new = options[:requires_new] || !last_transaction_joinable
123: 
124:         transaction_open = false
125:         begin
126:           if block_given?
127:             if requires_new || open_transactions == 0
128:               if open_transactions == 0
129:                 begin_db_transaction
130:               elsif requires_new
131:                 create_savepoint
132:               end
133:               increment_open_transactions
134:               transaction_open = true
135:             end
136:             yield
137:           end
138:         rescue Exception => database_transaction_rollback
139:           if transaction_open && !outside_transaction?
140:             transaction_open = false
141:             decrement_open_transactions
142:             if open_transactions == 0
143:               rollback_db_transaction
144:             else
145:               rollback_to_savepoint
146:             end
147:           end
148:           raise unless database_transaction_rollback.is_a?(ActiveRecord::Rollback)
149:         end
150:       ensure
151:         @transaction_joinable = last_transaction_joinable
152: 
153:         if outside_transaction?
154:           @open_transactions = 0
155:         elsif transaction_open
156:           decrement_open_transactions
157:           begin
158:             if open_transactions == 0
159:               commit_db_transaction
160:             else
161:               release_savepoint
162:             end
163:           rescue Exception => database_transaction_rollback
164:             if open_transactions == 0
165:               rollback_db_transaction
166:             else
167:               rollback_to_savepoint
168:             end
169:             raise
170:           end
171:         end
172:       end
update(sql, name = nil)

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

[ show source ]

    # File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 48
48:       def update(sql, name = nil)
49:         update_sql(sql, name)
50:       end
Protected Instance methods
delete_sql(sql, name = nil)

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

[ show source ]

     # File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 269
269:         def delete_sql(sql, name = nil)
270:           update_sql(sql, name)
271:         end
insert_sql(sql, name = nil, pk = nil, id_value = nil, sequence_name = nil)

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

[ show source ]

     # File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 258
258:         def insert_sql(sql, name = nil, pk = nil, id_value = nil, sequence_name = nil)
259:           execute(sql, name)
260:           id_value
261:         end
sanitize_limit(limit)

Sanitizes the given LIMIT parameter in order to prevent SQL injection.

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.

Returns the sanitized limit parameter, either as an integer, or as a string which contains a comma-delimited list of integers.

[ show source ]

     # File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 280
280:         def sanitize_limit(limit)
281:           if limit.to_s =~ /,/
282:             limit.to_s.split(',').map{ |i| i.to_i }.join(',')
283:           else
284:             limit.to_i
285:           end
286:         end
select(sql, name = nil)

Returns an array of record hashes with the column names as keys and column values as values.

[ show source ]

     # File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 253
253:         def select(sql, name = nil)
254:         end
update_sql(sql, name = nil)

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

[ show source ]

     # File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 264
264:         def update_sql(sql, name = nil)
265:           execute(sql, name)
266:         end