Add Database#transaction :skip_transaction option to skip creating a …

…transaction or savepoint

Use this to support skipping transactions in
Dataset#{import,paged_each}.  Also use this to simplify other code
that used conditionals for whether or not to support transactions.

CHANGELOG

@@ -1,5 +1,9 @@
 === master
 
+* Support skipping transactions in Dataset#{import,paged_each} using :skip_transaction option (jeremyevans)
+
+* Add Database#transaction :skip_transaction option to skip creating a transaction or savepoint (jeremyevans)
+
 * Stop using a transaction for a single query if calling Dataset#import with a dataset (jeremyevans)
 
 * Add paged_update_delete plugin for paged deletes and updates (jeremyevans) (#2080)

lib/sequel/database/schema_methods.rb

@@ -712,8 +712,9 @@ def create_table_indexes_from_generator(name, generator, options)
       e = options[:ignore_index_errors] || options[:if_not_exists]
       generator.indexes.each do |index|
         begin
-          pr = proc{index_sql_list(name, [index]).each{|sql| execute_ddl(sql)}}
-          supports_transactional_ddl? ? transaction(:savepoint=>:only, &pr) : pr.call
+          transaction(:savepoint=>:only, :skip_transaction=>supports_transactional_ddl? == false) do
+            index_sql_list(name, [index]).each{|sql| execute_ddl(sql)}
+          end
         rescue Error
           raise unless e
         end

lib/sequel/database/transactions.rb

@@ -166,6 +166,8 @@ def rollback_checker(opts=OPTS)
     #               uses :auto_savepoint, you can set this to false to not use a savepoint.
     #               If the value given for this option is :only, it will only create a
     #               savepoint if it is inside a transaction.
+    # :skip_transaction :: If set, do not actually open a transaction or savepoint,
+    #                      just checkout a connection and yield it.
     #
     # PostgreSQL specific options:
     #
@@ -193,6 +195,10 @@ def transaction(opts=OPTS, &block)
         end
       else
         synchronize(opts[:server]) do |conn|
+          if opts[:skip_transaction]
+            return yield(conn)
+          end
+
           if opts[:savepoint] == :only
             if supports_savepoints?
               if _trans(conn)

lib/sequel/dataset/actions.rb

@@ -356,6 +356,8 @@ def get(column=(no_arg=true; nil), &block)
     #            This does not have an effect if +values+ is a Dataset.
     # :server :: Set the server/shard to use for the transaction and insert
     #            queries.
+    # :skip_transaction :: Do not use a transaction even when using multiple
+    #                      INSERT queries.
     # :slice :: Same as :commit_every, :commit_every takes precedence.
     def import(columns, values, opts=OPTS)
       return insert(columns, values) if values.is_a?(Dataset)
@@ -588,6 +590,8 @@ def multi_insert(hashes, opts=OPTS)
     #                   if your ORDER BY expressions are not simple columns, if they contain
     #                   qualified identifiers that would be ambiguous unqualified, if they contain
     #                   any identifiers that are aliased in SELECT, and potentially other cases.
+    # :skip_transaction :: Do not use a transaction. This can be useful if you want to prevent
+    #                      a lock on the database table, at the expense of consistency.
     #
     # Examples:
     #
@@ -1111,11 +1115,9 @@ def _aggregate(function, arg)
     # are provided. When only a single value or statement is provided, then yield
     # without using a transaction.
     def _import_transaction(values, trans_opts, &block)
-      if values.length > 1
-        @db.transaction(trans_opts, &block)
-      else
-        yield
-      end
+      # OK to mutate trans_opts as it is generated by _import
+      trans_opts[:skip_transaction] = true if values.length <= 1
+      @db.transaction(trans_opts, &block)
     end
 
     # Internals of +select_hash+ and +select_hash_groups+

lib/sequel/extensions/migration.rb

@@ -482,11 +482,7 @@ def checked_transaction(migration, &block)
         @use_transactions
       end
 
-      if use_trans
-        db.transaction(&block)
-      else
-        yield
-      end
+      db.transaction(:skip_transaction=>use_trans == false, &block)
     end
 
     # Load the migration file, raising an exception if the file does not define

lib/sequel/model/base.rb

@@ -1945,8 +1945,10 @@ def checked_save_failure(opts)
       end
 
       # If transactions should be used, wrap the yield in a transaction block.
-      def checked_transaction(opts=OPTS)
-        use_transaction?(opts) ? db.transaction({:server=>this_server}.merge!(opts)){yield} : yield
+      def checked_transaction(opts=OPTS, &block)
+        h = {:server=>this_server}.merge!(opts)
+        h[:skip_transaction] = true unless use_transaction?(opts)
+        db.transaction(h, &block)
       end
 
       # Change the value of the column to given value, recording the change.
@@ -2148,8 +2150,9 @@ def [](*args)
       #   # DELETE FROM artists WHERE (id = 2)
       #   # ...
       def destroy
-        pr = proc{all(&:destroy).length}
-        model.use_transactions ? @db.transaction(:server=>opts[:server], &pr) : pr.call
+        @db.transaction(:server=>opts[:server], :skip_transaction=>model.use_transactions == false) do
+          all(&:destroy).length
+        end
       end
 
       # If there is no order already defined on this dataset, order it by

spec/core/dataset_spec.rb

@@ -3374,6 +3374,14 @@ def supports_cte_in_subselect?; false end
       'COMMIT']
   end
 
+  it "should accept a :skip_transaction option to skip transactions" do
+    @ds.import([:x, :y], [[1, 2], [3, 4]], :skip_transaction=>true)
+    @db.sqls.must_equal [
+      "INSERT INTO items (x, y) VALUES (1, 2)",
+      "INSERT INTO items (x, y) VALUES (3, 4)",
+    ]
+  end
+
   it "should accept a columns array and a dataset" do
     @ds2 = @ds.from(:cats).filter(:purr => true).select(:a, :b)
 
@@ -5458,6 +5466,11 @@ class << Sequel
     sqls[-1].must_equal 'COMMIT'
   end
 
+  it "should not use a transaction if the :skip_transaction option is given" do
+    @ds.paged_each(:skip_transaction=>true, &@proc)
+    @ds.db.sqls.must_equal ['SELECT * FROM test ORDER BY x LIMIT 1000 OFFSET 0']
+  end
+
   it "should use a limit and offset to go through the dataset in chunks at a time" do
     @ds.paged_each(&@proc)
     @ds.db.sqls[1...-1].must_equal ['SELECT * FROM test ORDER BY x LIMIT 1000 OFFSET 0']

spec/model/record_spec.rb

@@ -272,7 +272,7 @@ def o.autoincrementing_primary_key() :y end
     DB.sqls.must_equal ["BEGIN", "UPDATE items SET y = NULL WHERE (id = 3)", "COMMIT"]
   end
 
-  it "should use :transaction option if given" do
+  it "should use :transaction option if given to override use_transactions setting" do
     o = @c.load(:id => 3, :x => 1, :y => nil)
     o.use_transactions = true
     o.save(:columns=>:y, :transaction=>false)
@@ -283,6 +283,13 @@ def o.autoincrementing_primary_key() :y end
     DB.sqls.must_equal ["BEGIN", "UPDATE items SET y = NULL WHERE (id = 3)", "COMMIT"]
   end
 
+  it "should respect :skip_transaction=>true option if given" do
+    o = @c.load(:id => 3, :x => 1, :y => nil)
+    o.use_transactions = true
+    o.save(:columns=>:y, :skip_transaction=>true)
+    DB.sqls.must_equal ["UPDATE items SET y = NULL WHERE (id = 3)"]
+  end
+
   it "should rollback if before_save calls cancel_action and raise_on_save_failure = true" do
     o = @c.load(:id => 3, :x => 1, :y => nil)
     o.use_transactions = true