Support default transaction mode.

* Add "default_transaction_mode" to "options" parameter of
  SQLite3::Database.new.
  It is used as transaction mode when SQLite3::Database#transaction is
  called without "mode" argument.

Author: masamitsu-murase

lib/sqlite3/database.rb

@@ -119,6 +119,7 @@ def initialize file, options = {}, zvfs = nil
       @type_translation = options[:type_translation]
       @type_translator  = make_type_translator @type_translation
       @readonly         = mode & Constants::Open::READONLY != 0
+      @default_transaction_mode = options[:default_transaction_mode] || :deferred
 
       if block_given?
         begin
@@ -622,8 +623,10 @@ def finalize
     # by SQLite, so attempting to nest a transaction will result in a runtime
     # exception.
     #
-    # The +mode+ parameter may be either <tt>:deferred</tt> (the default),
+    # The +mode+ parameter may be either <tt>:deferred</tt>,
     # <tt>:immediate</tt>, or <tt>:exclusive</tt>.
+    # If `nil` is specified, the default transaction mode, which was
+    # passed to #initialize, is used.
     #
     # If a block is given, the database instance is yielded to it, and the
     # transaction is committed when the block terminates. If the block
@@ -634,7 +637,8 @@ def finalize
     # If a block is not given, it is the caller's responsibility to end the
     # transaction explicitly, either by calling #commit, or by calling
     # #rollback.
-    def transaction( mode = :deferred )
+    def transaction( mode = nil )
+      mode = @default_transaction_mode if mode.nil?
       execute "begin #{mode.to_s} transaction"
 
       if block_given?

test/test_database.rb

@@ -624,5 +624,45 @@ def test_raw_float_infinity
       db.execute("insert into foo values (?)", Float::INFINITY)
       assert_equal Float::INFINITY, db.execute("select avg(temperature) from foo").first.first
     end
+
+    def test_default_transaction_mode
+      tf = Tempfile.new 'database_default_transaction_mode'
+      SQLite3::Database.new(tf.path) do |db|
+        db.execute("create table foo (score int)")
+        db.execute("insert into foo values (?)", 1)
+      end
+
+      test_cases = [
+        {mode: nil, read: true, write: true},
+        {mode: :deferred, read: true, write: true},
+        {mode: :immediate, read: true, write: false},
+        {mode: :exclusive, read: false, write: false},
+      ]
+
+      test_cases.each do |item|
+        db = SQLite3::Database.new tf.path, default_transaction_mode: item[:mode]
+        db2 = SQLite3::Database.new tf.path
+        db.transaction do
+          sql_for_read_test = "select * from foo"
+          if item[:read]
+            assert_nothing_raised{ db2.execute(sql_for_read_test) }
+          else
+            assert_raises(SQLite3::BusyException){ db2.execute(sql_for_read_test) }
+          end
+
+          sql_for_write_test = "insert into foo values (2)"
+          if item[:write]
+            assert_nothing_raised{ db2.execute(sql_for_write_test) }
+          else
+            assert_raises(SQLite3::BusyException){ db2.execute(sql_for_write_test) }
+          end
+        end
+      ensure
+        db.close if db && !db.closed?
+        db2.close if db2 && !db2.closed?
+      end
+    ensure
+      tf.unlink if tf
+    end
   end
 end