The Web Semantic

I recently ran across a project called ja.net that provides support for compilation of Java to .Net.  Since neo4j has such a dependency clean kernel, I decided to try ja.net as a way of making neo4j usefull under .Net. (no slight against the RESTful interfaces, but perhaps you’d like to run neo4j on .net as an embedded graph DB under .Net). Here’s my VS2010 with the neo4j.dll referenced, and the object browser showing the EmbeddedGraphDB class as a first class .Net object:

Step #1 Download stuff

Download the neo4j kernel source and expand into a working directory. http://neo4j.org/download

Download the geronimo JTA spec src jar and expand under neo4j’s src/main/java directory. 

Install Ja.net from http://www.janetdev.org/. 

Step #2 Compile neo4j kernel using Ja.Net

C:\neo4j-kernel-1.0\src>c:\opt\java\Ja.NET\bin\javac -bam:neo4j.dll main

You can compile first then using the “bam” command to create the dll, or do it in one pass as I’ve done here.  You’ll see warnings, most look like compiler warnings, one may be of concern.  For now let’s just experiment.  No garauntees, promises, etc. 

Step #3 Create a C# console app, reference your newly created .dll, and give neo4j on .net a run.  Here’s my sample code:

class Program
{
static void Main(string[] args)
{
var graphDb = new EmbeddedGraphDatabase("graphdb");
var tx = graphDb.beginTx();
try
{
var firstNode = graphDb.createNode();
var secondNode = graphDb.createNode();
var relationship = firstNode.createRelationshipTo(
secondNode, DynamicRelationshipType.withName("KNOWS"));
firstNode.setProperty("message", "Hello, ");
secondNode.setProperty("message", "world!");
relationship.setProperty("message", "brave Neo4j ");
var i = graphDb.getAllNodes().iterator();
while (i.hasNext()) {
    var n = ((Node)i.next());
    if (n.hasProperty("message"))
    Console.WriteLine(n.getProperty("message"));
}
Console.WriteLine("bye");
tx.success();
}
finally
{
   tx.finish();
   graphDb.shutdown();
}
Console.ReadLine();
}

“show the latest ….” is a common prefix to user stories these days.  Others have noted the same and given this symptom a moniker; ”The real time web“.  Typically we just throw things into a table with an indexed timestamp column and query accordingly.

In jo4neo, finding the most recent additions requires two simple steps:

1. annotation your type with @neo(recency=true)
2. use the ObjectGraph.getMostRecent() method to retrieve the latest inserts.

In this small example, we’re indicating to jo4neo that we’d like it to remember our “Post” inserts in most recent order. » Read the rest of this entry «

Graphs in and of themselves are not self indexing like relational databases, however, you can construct indexes via strong relationships between the nodes of interest.  The pattern I’ll be discussing in this post maps time (year, month, day, hour) into a graph format as nodes and edges.  Once time, or some subset, is represented as a graph we can then associate events or moment intervals as nodes related to a particular hour of a particular day, month and year.  ( This post is based on a full example here.) » Read the rest of this entry «

neoblog is a simple application I built to test drive jo4neo.  You are welcome to browse the code here for details not covered in this post. It demonstrates the feasibility of utilizing view tier objects to persist graph relationships.

neoblog with 3 posts

» Read the rest of this entry «

Roles and Users is a classic domain model well suited to representation as a directed graph. The neo4j team has provided us with a good summary of how to implement this pattern using neo4j here . Utilizing jo4neo we can also solve this problem via a combination of the neo graph database and simple java objects.  The code and maven build for this example are posted here.  I encourage you to run the example and browse the code.  We’ll need two domain classes, » Read the rest of this entry «