For the first draft, I just wanted to add support for Spatialite, a spatially enabled version of SQLite. Since SQLite is already supported, this turned out to be relatively easy – though in hindsight, I may not even have implemented it in the easiest way possible – but I’ll get to that in another post.

So, each database backend is in a namespace called htsql_[name], and they all subclass files in the main htsql namespace. I started off by cloning the htsql_sqlite tree into a new namespace called htsql_spatialite, and ripped out most of the code, leaving me with a basic structure. I then subclassed any SQLite classes I wanted to override – most importantly:

1. Changed connect.py to import pyspatialite instead of pysqlite2.
2. Added my own Column and Data types (Domains) in domain.py
3. Modified introspect.py to handle my custom Domains, as well as to handle the blank Column type sometimes given for Geometry columns

I also, and here is where most of my functionality was added, overrode a few classes in tr/serializer.py:

1. Class SpatialiteSerializeLeafReference(subclassing SerializeLeafReference) tests if I am selecting a Geometry column, and if I am, wraps it in the “AsText” function, to return WKT.
2. a new Adaptor, FormatGeometry, which handled the representation of the WKT when returned to the client. Right now, only HTML is supported, but JSON, CSV, and the rest are easy to add in the same way.

The last thing you have to do is add a line in setup.py to point to your new database engine’s entry point – it is in a list called ENTRY_POINTS.

Interestingly, I think I could better utilize the plugin architecture – but as I’m just discovering HTSQL, and there isn’t all that many samples, nor much documentation, I’m pretty happy with what I accomplished.

You can see the full source of my additions at https://bitbucket.org/lokkju/htsql-appengine/src/3d7b7d8e8580/

First, create a role that will own the tables within the template database:
psql -c "CREATE ROLE gisgroup;"

Second, create and populate the template database:

createdb -E UNICODE template_postgis
createlang -d template_postgis plpgsql
psql -d template_postgis < /usr/share/postgresql/8.4/contrib/postgis-1.5/postgis.sql
psql -d template_postgis < /usr/share/postgresql/8.4/contrib/postgis-1.5/spatial_ref_sys.sql
psql -d template_postgis < /usr/share/postgresql/8.4/contrib/postgis_comments.sql


Third, set the ownership to the role you created:

psql -c "ALTER TABLE geometry_columns OWNER TO gisgroup;" template_postgis
psql -c "ALTER TABLE spatial_ref_sys OWNER TO gisgroup;" template_postgis


Fourth, we create the user for our database:

psql -c "CREATE USER yourgisuser WITH PASSWORD 'yourpassword';"
psql -c "GRANT gisgroup TO yourgisuser;"


Fifth, and last, we create a new postgis enable database:
createdb -T template_postgis -O yourgisuser your_new_postgis_database

I needed to do this recently, and found one hint on how to get it working at http://forums.asp.net/t/1328690.aspx . They key is to use Process to launch the application you need, then attach to it.

Sample code in C#:


Microsoft.Office.Interop.Word.Application app = null;
Process proc = null;
Document doc = null;
try
{
ProcessStartInfo procinfo = new ProcessStartInfo(WORD_PATH, "");
procinfo.WorkingDirectory = AppDomain.CurrentDomain.BaseDirectory;
procinfo.CreateNoWindow = true;
procinfo.WindowStyle = ProcessWindowStyle.Hidden;
proc = Process.Start(procinfo);
proc.WaitForInputIdle();
app = (Microsoft.Office.Interop.Word.Application)System.Runtime.InteropServices.Marshal.GetActiveObject("Word.Application");
if (app == null) { throw new Exception("Word not found"); }
app.Visible = false;
app.DisplayAlerts = WdAlertLevel.wdAlertsNone;
#region Declare Params
object fileName = filename;
object ConfirmConversions = false;
object ReadOnly = true;
object AddToRecentFiles = Type.Missing;
object PasswordDocument = Type.Missing;
object PasswordTemplate = Type.Missing;
object Revert = Type.Missing;
object WritePasswordDocument = Type.Missing;
object WritePasswordTemplate = Type.Missing;
object Format = Type.Missing;
object Encoding = Type.Missing;
object Visible = false;
object OpenAndRepair = Type.Missing;
object DocumentDirection = Type.Missing;
object NoEncodingDialog = Type.Missing;
object XMLTransform = Type.Missing;
#endregion
doc = app.Documents.Open(ref fileName, ref ConfirmConversions, ref ReadOnly, ref AddToRecentFiles, ref PasswordDocument, ref PasswordTemplate, ref Revert, ref WritePasswordDocument, ref WritePasswordTemplate, ref Format, ref Encoding, ref Visible, ref OpenAndRepair, ref DocumentDirection, ref NoEncodingDialog, ref XMLTransform);
// DO WHATEVER YOU NEED TO HERE
}
finally
{
object saveChanges = WdSaveOptions.wdDoNotSaveChanges;
object OriginalFormat = Type.Missing;
object RouteDocument = Type.Missing;
try
{
((_Document)doc).Close(ref saveChanges, ref OriginalFormat, ref RouteDocument);
doc = null;
}
catch { }
try
{
((Microsoft.Office.Interop.Word._Application)app).Quit(ref saveChanges, ref OriginalFormat, ref RouteDocument);
app = null;
}
catch { }
try
{
proc.Kill();
}
catch { }
}