Last week, Mike Wynholds presented at the inaugural Los Angeles No SQL meetup. The movement to these non-traditional data storage systems has exploded in the last year, and we had a chance to use Cassandra in one of our client’s projects. Cassandra is a column based datastore developed within Facebook, and open-sourced as a top-level Apache project. It is being used by its creators as well as Digg, Twitter, Reddit, Rackspace, and many others. For the meetup, our presentation covered what is Cassandra’s structure, how we used it, the challenges we faced, and the lessons learned. You can watch the presentation below, or you can grab the presentation with this PDF, and from its original Keynote file. And feel free to ask questions and leave comments below!
Author Archive for mike
I have been working on a web app for one of our clients that includes a pretty interactive AJAX / Web 2.0 component within it. This component is essentially a simplified drag-and-drop book publishing tool, which allows users to upload images and then to arrange them on predefined templates in order to create a book.
We chose to use the Dojo Toolkit (version 0.4.2) for both the AJAX (ie: remote calls to the server) and the Widegtry side of the Web 2.0 style. It’s been working fairly well. Dojo has a lot of functionality, but also has a few areas that still need some refinement. The most interesting / infuriating to me so far has to do with Dojo drag-and-drop functionality within IE.
Dojo’s facility for drag-and-drop is essentially composed of three components:
- Drag-and-Drop Manager
- Drag Sources
- Drop Targets
It intuitively makes a lot of sense. You create drag sources and drop targets and out of the box they actually work pretty well. Dojo uses a form of JavaScript inheritance to allow you to create drag copy sources or drag move sources, each of which have different behaviors. You can also reassign specific functions on your drag sources or drop targets in order to customize their behaviors.
I developed and debugged the app in Firefox and Firebug, as we all do. But when it came time to check that everything works in IE, I ran in to one bug in particular that stumped me for two entire days, and frustrated me to no end. At a certain point in using the app, my ability to drop objects on their drop targets was broken. It only happened in IE (I was using IE 6 for Windows), and the error I got was the always helpful “Unexpected error”.
What I found was that the following code, which creates a drop target, also registers the drop target with the Drag and Drop Manager.
var imageTarget = new dojo.dnd.HtmlDropTarget(imageDiv, ['galleryImages']); imageDiv.imageTarget = imageTarget;
As a matter of fact, the Drag and Drop Manager, which is a global singleton, keeps a registry of all drag sources and drop targets created. Later on in the flow of my application, some of these drop targets need to be re-rendered, and to do so I actually delete the DOM node and re-create it, using the following code:
dojo.dom.destroyNode(pageContainerDiv);
The destroyNode() function is supposed to be memory-leak-friendly. But after I have done that, and created a new drop target where that one once was, when I try to drop another drag source on to it, I get the “Unexpected error” exception in JavaScript. And again, this only happens in IE. Firefox works fine. I finally realized that, even though the drop targets are automatically (and outside my knowledge for a long time) being registered with the Drag and Drop Manager, they must be explicitly unregistered before they are destroyed, otherwise this error occurs. I added the following code to do so.
dojo.dnd.dragManager.unregisterDropTarget(imageDiv.imageTarget);
And now everything works perfectly!
We have been using HSQL in-memory along with DBUnit for unit testing lately, and I found an issue using the most recent version of each. Basically, HSQL has added a new data type, BOOLEAN, which replaces BIT. But DBUnit is not updated to support this, and an error is throw when you attempt to insert some BOOLEAN data using DBUnit.
The error looks like this:WARNING - TABLE.COLUMN data type (16, 'BOOLEAN') not recognized and will be ignored. See FAQ for more information.
HsqlDataTypeFactory.java
package company.project.test; import org.apache.commons.logging.*; import org.dbunit.dataset.datatype.*; import java.sql.*; public class HsqlDataTypeFactory extends DefaultDataTypeFactory { private static final Log log = LogFactory.getLog(HsqlDataTypeFactory.class); public DataType createDataType(int sqlType, String sqlTypeName) throws DataTypeException { if (sqlType == Types.BOOLEAN) { return DataType.BOOLEAN; } return super.createDataType(sqlType, sqlTypeName); } }
Then, in order to use this data type factory, just set a property on the IDatabaseConnection DBUnit object in your code (here is an example method):
protected IDatabaseConnection getConnection() throws Exception { IDatabaseConnection connection = new DatabaseConnection(dataSource.getConnection()); DatabaseConfig config = connection.getConfig(); config.setProperty(DatabaseConfig.PROPERTY_DATATYPE_FACTORY, new HsqlDataTypeFactory()); return connection; }
