Lucene.Net.ObjectMapping for .Net Standard 2.0

It’s been a long time since I’ve done some work on my Lucene.Net.ObjectMapping library. Recently I accepted a pull request that added support for the 4.8 beta releases of Lucene.Net itself, but when I involuntarily needed to updated one of my services to bring it up to speed with running in a Docker container, I decided that it was about time to update Lucene.Net.ObjectMapping for .Net Standard 2.0. The last time I used the library in a Docker container, ASP.NET vNext RC1 was just about to become final. so that’s a long time ago. Accordingly, there was quite a bit of work to understand the changes needed: both in .Net (and ASP.NET) between the 1.0 RC1 and the .Net Standard 2.0 releases, and also between the Lucene.Net 3.x and 4.8 releases. Luckily, the latter was largely taken care of by the pull request for the library itself. The former however proved a bit challenging. After all, the toolset has changed significantly.

Updated Sources

To cut a long story short, the updated sources are now available on GitHub. I decided to track it in a separate branch for better isolation. This new branch is aptly called netstandard. I’ll try to stay up-to-date with the more recent releases of Lucene.Net, and also with .Net Standard 2.0. That is, provided that I find the time for it. You may notice that the project files have become quite a bit simpler. That’s certainly one change in .Net Standard and Core that I welcome. The other is the better integration of Nuget for package referencing and package creation/pushing.

Updated Unit Tests

As a side effect, I also figured that it was going to be easier to update NUnit to the latest version, since its toolset is also well integrated with the new dotnet toolset. Since I’m doing all changes through VSCode and with building/testing/packaging in Docker containers based on the microsoft/aspnetcore-build:2 images, I wanted to keep it simple. The good thing here is that the dotnet toolset seems to offer really everything I need for this, and is suprisingly easy to handle, especially when compared to the RC1 version.

Updated Nuget Package

As I’ve mentioned in the beginning, I primarily made this effort because I needed a newer version of Lucene.Net with compatibility for .Net Standard 2.0. As a result, I published a new RC build as a Nuget package too. It is built on the latest Lucene.Net 4.8 beta release and currently supports only .Net Standard 2.0. If there’s a great demand for it, I’ll see if I can add support for other targets – or accept pull requests accordingly.


Nothing much besides the obvious: .Net Standard seems to be in a good shape wrt libraries and toolset, as well as support on Linux. There are a few gotchas but overall nothing much of a problem. Lucene.Net is still somewhat badly documented itself, and the tracking of braking changes between major/minor versions (and in fact also revisions/beta releases of the same major/minor) could be greatly improved. An online documentation would be very useful – maybe it exists, and I just haven’t found it? In any case, skimming through the Lucene.Net sources on GitHub works too, though being much slower.

You can find more information about object mapping for Lucene.Net on the Lucene.Net.ObjectMapping page.

Azure Queue Agent – Introduction

For a small side project I’ve been working on I needed a way to schedule background tasks and handle them on a pool of workers. Since I was planning to run this on Azure, the Queues offered with Azure Storage seemed to be a no-brainer. Even more so since the Azure Scheduler, which can be used to periodically execute some action, can also be used to add messages to Queues. I figured that I wasn’t the only one needing something to handle such tasks, so I decided to build a lightweight open-source library for this.

Enter Azure Queue Agent (AQuA)

AQuA comes with two main components: a Producer and a Consumer. As the names suggest, the Producer can be used to produce (i.e. enqueue) new jobs, while the Consumer can be used to consume (i.e. dequeue and then handle) jobs from the queue. Job Descriptors are used to define which job should be executed and what parameters should be used for the execution. They are encoded as simple JSON objects like the one below, i.e. they can also easily be written manually (e.g. when used with the Azure Scheduler). That said, with AQuA it is very simple to build a scalable and robust collection of workers which take care of all your background processing jobs.

{ "Job": "HelloWho", "Properties": { "Who": "World" } }

The above example for instance would queue the HelloWho job, which does nothing more but print the value of the Who parameter on stdout like this: “Hello, <Who>!”. In addition, the Azure Queue Agent Consumer can be configured to either delete or requeue messages which were badly formatted, using unknown jobs or which could not be executed successfully, such that you can even use a single queue for multiple different pools of workers, should you ever find yourself in that situation.

Getting Started

The Azure Queue Agent is available as a NuGet package, currently however only in pre-release. You can get it like this:

Install-Package aqua.lib -Pre

Once this is done, you need to create an instance of Producer (if you want to create job requests from your code), and an instance of Consumer (for when you want to handle job requests).

// Setup and initialization
JobFactory factory = new JobFactory();

// Register all the jobs you want your consumer to be able to handle.

// Use the storage account from the emulator with queue "jobs".
ConnectionSettings connection = new ConnectionSettings("jobs");

Producer producer = new Producer(connection, factory);
Consumer consumer = new Consumer(connection, factory);

// Produce (i.e. enqueue) a HelloWho job request.
HelloWho job = new HelloWho() { Who = "Azure Queue Agent Example" };

// Consume (i.e. dequeue and handle) a job request.

This should get you going for now. I’ll follow up with more later. Oh, and you can read the sources on GitHub.

Offline JSON Pretty Printing

Today when you’re dealing with Web APIs, you often find yourself in the situation of handling JSON, either in the input for these APIs or in the output, or both. Some browsers have the means to pretty print the JSON from their dev tools. But you don’t always have that opportunity. That’s why there are tools to pretty print JSON. I’ve found quite a few of them on the web, but all the ones I’ve found have one terrible flaw: they actually send the JSON you’re trying to pretty print to the server (*shudder*). I don’t want my JSON data (sensitive or not) to be sent to some random servers!

All your JSON are belong to us!

Now as I wrote, I don’t particularly like the fact that my JSON data is sent over the wire for pretty printing. It may not be super secret or anything, but in these days, you cannot be careful enough. Besides, it’s completely unnecessary to do it. All you need is already in your browser! So I quickly built my own JSON pretty printer (and syntax highlighter). You can find it right here.

Offline JSON Pretty Printing to the Rescue

Actually, the design is very simple. All my JSON pretty printer is doing, is to take your JSON input and try to parse it as JSON in the browser.


If that fails, I’m showing the parsing error and it’s done. If it succeeds, I get back a JavaScript object/array/value, which then I’m inspecting. For objects, I’m using basic tree navigation to go through all the properties and nested objects/arrays/values for pretty printing. That’s it, really simple. No need to transmit the data anywhere — it stays right in your browser!

So like it, hate it, use it or don’t: JSON Pretty Printer

LINQ with Lucene.Net.ObjectMapping

Last time I mentioned that I started to work on supporting LINQ with Lucene.Net.ObjectMapping. That includes LINQ queries like the following:

using (Searcher searcher = new IndexSearcher(directory))
    IQueryable<BlogPost> posts =
        from post in searcher.AsQueryable<BlogPost>()
        where obj.Tag == "lucene"
        orderby obj.Timestamp descending
        select post;

Now granted, the above example is a very basic one. So here’s a short list of other methods on IQueryable<T> that are already supported at this point: Any *, Count *, First *, FirstOrDefault *, OrderBy, OrderByDescending, Single *, SingleOrDefault *, Skip, Take, ThenBy, ThenByDescending, and finally Where.

* Method is supported both with and without a filter predicate.

With this, it becomes easy to build paging based on objects you get back as a result of a query on Lucene.Net. I’m still working on improving the supported filter expressions (most of all for Where, but all the other filterable methods naturally profit too). For instance, with the default JSON-based object mapping it is already possible to search for entries in a dictionary that maps a string to another property or object. Say you have a set of classes, defined as follows.

public class MyClass
    public int Id { get; set; }
    public Dictionary<string, MyOtherClass> Map { get; set; }

public class MyOtherClass
    public string Text { get; set; }
    public int Sequence { get; set; }
    public DateTime Timestamp { get; set; }

Now you can actually search for instances of MyClass that satisfy certain conditions in the Map dictionary, like this:

var query = from c in searcher.AsQueryable<MyClass>()
            where c.Map["MyKey"].Sequence == 123
            select c;

Since the items in the dictionary are mapped to analyzed fields in the Lucene.Net document, we can search on them!

Delete and Update By Query

Now since I have this query expression binder to create Lucene.Net queries based on LINQ filter expressions, I’ve added an extension method to update and one to delete documents that match a query. So it is now possible to do this:

indexWriter.Delete<MyClass>(x => x.Id == 1234);
indexWriter.Update(myObject, x => x.Id == myObject.Id);

Call to Action

Now with all this said, I’m looking for volunteers to help me get more coverage on the LINQ queries, because that’s definitely where the weak spot is right now. If you’re interested, leave a comment here or on GitHub.