Add Database#checkout, Connection#release for non block connection use (#38)

src/db/connection.cr

@@ -71,9 +71,16 @@ module DB
     protected def after_release
     end
 
+    # return this connection to the pool
+    # managed by the database. Should be used
+    # only if the connection was obtained by `Database#checkout`.
+    def release
+      @database.return_to_pool(self)
+    end
+
     # :nodoc:
     def release_from_statement
-      @database.return_to_pool(self) if @auto_release && !@transaction
+      self.release if @auto_release && !@transaction
     end
 
     # :nodoc:

src/db/database.cr

@@ -94,18 +94,26 @@ module DB
     end
 
     # yields a connection from the pool
-    # the connection is returned to the pool after
+    # the connection is returned to the pool
     # when the block ends
     def using_connection
-      connection = @pool.checkout
-      connection.auto_release = false
+      connection = self.checkout
       begin
         yield connection
       ensure
-        return_to_pool connection
+        connection.release
       end
     end
 
+    # returns a connection from the pool
+    # the returned connection must be returned
+    # to the pool by explictly calling `Connection#release`
+    def checkout
+      connection = @pool.checkout
+      connection.auto_release = false
+      connection
+    end
+
     # yields a `Transaction` from a connection of the pool
     # Refer to `BeginTransaction#transaction` for documentation.
     def transaction