XmlSerializer – Check if property was present in XML

Recently I was parsing a large amount of XML files using the XmlSerializer class. While implementing the parser I came across a requirement where I had to check if a given property was null because it was specified as null or because the value was not present in the XML.

At first this caused me some headache because accessing the underlying XML file violates the abstraction provided by the serializer. Luckily, I recognised that the generated entity class (generated from XSD.exe) contains a lot of properties with the name <PropertyName>Specified. This is a very neat feature of the XmlSerializer. If you add a property with that name scheme it automatically sets the property to true when the corresponding element is present in the XML.

The property could look like this:

[System.Xml.Serialization.XmlIgnoreAttribute]
public bool MyPropertySpecified { get; set; }

Note: XmlIgnore is necessary to avoid having the artificial property serialised into XML when using the XmlSerializer to write XML. More details on the behaviour can be found in the class documentation here.

Logstash – File input not working on Windows

Logstash is a great tool to transform the information stored in unstructured log files into a structured format. When using it on a Windows machine there are several things you should pay attention to (and which are not 100% documented).

Let’s say you want to use a file input and specify it in this way:

input {
  file{
    path => ["C:\Logs\*.logs"]
  }
}

When you run Logstash nothing happens and your files are not processed.

The reason for that is pretty simple: Logstash doesn’t like the \ and because of that it does not recognise the path properly. So simply change the config to look like this:

input {
  file{
    path => ["C:/Logs/*.logs"]
  }
}

Always use in Logstash configs and you will easily get around this problem. The problem is also known to the Logstash community (see this bug) but there is no fix in place yet.

Hint:

The mechanism for detecting which files have been written and which log entries are new is also not working correctly on Windows (see this bug here). The link also contains information on how to get around this problem.

SQL Server Compact Edition – Still an option for lightweight persistence?

Recently, I was looking for a lightweight database for a small, independent application. One requirement was an easy deployment without installation of additional software on the server. The first thing that came to my mind was SQL Server Compact Edition. Technically it fulfilled all requirements perfectly but than I stumbled across this Connect Article.

“SQL Server compact edition is in deprecation mode with no new releases planned near future”

Sadly this disqualifies SQL Server Compact Edition for the use in a productive application and the recommended SQL Server Express or LocalDB do not really replace it.

Now the big question is, what to use instead of SQL Server Compact Edition for the use case of a lightweight, easy to deploy database on a Windows Server?

SSIS – Unexpected Termination

I did observe a confusing behaviour after patching a SQL Server 2012 to Service Pack 2. Some of the SSIS jobs running on that server started to fail with the message Unexpected Termination while most of the other jobs just worked as before.

Unexpected Termination can have multiple causes and if you search for that error in the internet you can find a bunch of different reasons and solutions. But non of them worked and to make the situation worse the jobs running on other servers without the Service Pack still worked. So I started looking into the known issues of the Service Pack and luckily I found this link: http://support.microsoft.com/kb/2991528 

The error did not exactly match the entry I could find in the Event Viewer but all failing jobs used DT_TEXT or DT_NTEXT. I decided to risk installing the Cumulative Update (http://support.microsoft.com/kb/2983175) containing the fix. After this, the jobs started to work just fine. So in the end the solution was extremely simple.

This is just one possible solution for the Unexpected Termination error but if you experience this error after installing Service Pack 2 you should definitely check if this is also your problem.

JavaScript – Documenting optional parameter

JavaScript is an awesome language but due to its nature parameter documentation is pretty important especially when it come to optional parameters. If you want to create a method like this:

module.exports.create = function (callback) {
    // Do something
    if (callback) {
        callback();
    }
}

Obviously, callback is an optional parameter but if we use this method in an IDE like JetBrains WebStorm it will always show us a wrong signature warning and other developers might think this parameter is mandatory.  We can overcome that situation by adding the correct comment on this method.

/**
 * The method does something. 
 * 
 * @param {requestCallback=} callback
 */
module.exports.create = function (callback) {
    // Do something
    if (callback) {
        callback();
    }
}

No the IDE an other developers looking at our method know that the parameter is optional and can use it like that. This syntax can be used to provide a lot of information on the different request parameter. This link contains a very detailed description.

Object # has no method ‘flash’ undefined TypeError: Object # has no method ‘flash’ at allFailed

Recently I was playing around with Passport.js in an Express application. I created a login route that logged like that:

passport.authenticate('local', {
    successRedirect: '/app',
    failureRedirect: '/login',
    failureFlash: false
});

Everything worked fine and I could login to my application but I also wanted to show a message when the login fails. So I changed my route to:

passport.authenticate('local', {
    successRedirect: '/app',
    failureRedirect: '/login',
    failureFlash: true
});

Instead of redirect back to the login page I got this exception:

Object #<IncomingMessage> has no method 'flash' undefined TypeError: Object #<IncomingMessage> has no method 'flash' at allFailed

The solution for this is simple. I forgot to include the connect-flash module that provides the flash method. So I changed my startup code:

var flash = require('connect-flash');
app.use(cookieParser());
app.use(flash());

Even so the solution is quite simple and somehow obvious. It doesn’t seem right that changing a property to true introduces the need for a new middleware.

Failed to bring availability group ” online

Recently, I was installing a SQL Server Availability Group on two VMs to verify some open questions I had. And I am surprised that the installation went pretty smoothly. But when I tried to create the availability group I got the following error message.

Failed to bring availability group ‘<availability group name>’ online. The operation timed out. Verify that the local Windows Server Failover Clustering (WSFC) node is online. Then verify that the availability group resource exists in the WSFC cluster. If the problem persists, you might need to drop the availability group and create it again.    

The message seemed to be pretty precise and I started verifying my WSFC configuration but unfortunately I couldn’t find any mistakes there. After searching for a while I found the following support post: http://support.microsoft.com/kb/2847723 It describes exactly my problem and the only thing I had to do was executing the following script:

USE [master]
GO
CREATE LOGIN [NT AUTHORITY\SYSTEM] FROM WINDOWS WITH DEFAULT_DATABASE=[master]
GO

GRANT ALTER ANY AVAILABILITY GROUP TO [NT AUTHORITY\SYSTEM]
GO
GRANT CONNECT SQL TO [NT AUTHORITY\SYSTEM]
GO
GRANT VIEW SERVER STATE TO [NT AUTHORITY\SYSTEM]
GO

It fixed the problem and I was able to create my availability group without any problems.