Transactions

* dsl, state checks
* define transaction sql commands in connection

src/db.cr

@@ -143,7 +143,10 @@ require "./db/session_methods"
 require "./db/disposable"
 require "./db/driver"
 require "./db/statement"
+require "./db/begin_transaction"
 require "./db/connection"
+require "./db/transaction"
+require "./db/statement"
 require "./db/pool_statement"
 require "./db/database"
 require "./db/pool_prepared_statement"

src/db/begin_transaction.cr

@@ -0,0 +1,17 @@
+module DB
+  module BeginTransaction
+    abstract def begin_transaction : Transaction
+
+    def transaction
+      tx = begin_transaction
+      begin
+        yield tx
+      rescue e
+        tx.rollback
+        raise e unless e.is_a?(DB::Rollback)
+      else
+        tx.commit unless tx.closed?
+      end
+    end
+  end
+end

src/db/connection.cr

@@ -21,10 +21,12 @@ module DB
   abstract class Connection
     include Disposable
     include SessionMethods(Connection, Statement)
+    include BeginTransaction
 
     # :nodoc:
     getter database
     @statements_cache = StringKeyCache(Statement).new
+    @transaction = false
     getter? prepared_statements : Bool
 
     def initialize(@database : Database)
@@ -42,10 +44,45 @@ module DB
     # :nodoc:
     abstract def build_unprepared_statement(query) : Statement
 
+    def begin_transaction
+      raise DB::Error.new("There is an existing transaction in this connection") if @transaction
+      @transaction = true
+      create_transaction
+    end
+
+    protected def create_transaction : Transaction
+      TopLevelTransaction.new(self)
+    end
+
     protected def do_close
       @statements_cache.each_value &.close
       @statements_cache.clear
       @database.pool.delete self
     end
+
+    # :nodoc:
+    def release_from_statement
+      @database.return_to_pool(self) unless @transaction
+    end
+
+    # :nodoc:
+    def release_from_transaction
+      @transaction = false
+    end
+
+    # :nodoc:
+    def perform_begin_transaction
+      self.unprepared.exec "BEGIN"
+    end
+
+    # :nodoc:
+    def perform_commit_transaction
+      self.unprepared.exec "COMMIT"
+    end
+
+    # :nodoc:
+    def perform_rollback_transaction
+      self.unprepared.exec "ROLLBACK"
+    end
   end
 end

src/db/database.cr

@@ -105,6 +105,14 @@ module DB
       end
     end
 
+    def transaction
+      using_connection do |cnn|
+        cnn.transaction do |tx|
+          yield tx
+        end
+      end
+    end
+
     # :nodoc:
     def retry
       @pool.retry do

src/db/error.cr

@@ -17,4 +17,7 @@ module DB
     def initialize(@connection)
     end
   end
+
+  class Rollback < Exception
+  end
 end

src/db/statement.cr

@@ -59,7 +59,7 @@ module DB
     end
 
     def release_connection
-      @connection.database.return_to_pool(@connection)
+      @connection.release_from_statement
     end
 
     # See `QueryMethods#exec`

src/db/transaction.cr

@@ -0,0 +1,43 @@
+module DB
+  abstract class Transaction
+    include Disposable
+
+    abstract def connection : Connection
+
+    def commit
+      close!
+    end
+
+    def rollback
+      close!
+    end
+
+    private def close!
+      raise DB::Error.new("Transaction already closed") if closed?
+      close
+    end
+  end
+
+  class TopLevelTransaction < Transaction
+    # :nodoc:
+    getter connection
+
+    def initialize(@connection : Connection)
+      @connection.perform_begin_transaction
+    end
+
+    def commit
+      @connection.perform_commit_transaction
+      close!
+    end
+
+    def rollback
+      @connection.perform_rollback_transaction
+      close!
+    end
+
+    protected def do_close
+      connection.release_from_transaction
+    end
+  end
+end