How do I stop rails from escaping values in SQL for a particular column?

Question

I'm trying to manually manage some geometry (spatial) columns in a rails model.

When updating the geometry column I do this in rails:

self.geom="POINTFROMTEXT('POINT(#{lat},#{lng})')"

Which is the value I want to be in the SQL updates and so be evaluated by the database. However by the time this has been through the active record magic, it comes out as:

INSERT INTO `places` (..., `geom`) VALUES(...,'POINTFROMTEXT(\'POINT(52.2531519,20.9778386)\')')

In other words, the quotes are escaped. This is fine for the other columns as it prevents sql-injection, but not for this. The values are guaranteed to be floats, and I want the update to look like:

INSERT INTO `places` (..., `geom`) VALUES(...,'POINTFROMTEXT('POINT(52.2531519,20.9778386)')')

So is there a way to turn escaping off for a particular column? Or a better way to do this?

(I've tried using GeoRuby+spatial adapter, and spatial adaptor seems too buggy to me, plus I don't need all the functionality - hence trying to do it directly).

Answer 1

1. You can use an after_save method, write them with a direct SQL UPDATE call. Annoying, but should work.

2. You should be able to create a trigger in your DB migration using the 'execute' method... but I've never tried it.

3. Dig into ActiveRecord's calculate functionality: max/min/avg, etc. Not sure whether this saves you much over the direct SQL call in after_save. See calculations.rb.

4. You could patch the function that quotes the attributes (looking for POINTFROMTEXT and then skip the quoting). This is pretty easy to find, as all the methods start with quote. Start with ActiveRecord::Base #quote_value.

Answer 2

The Rails Spatial Adapter should implement exactly what you need. Although, before I found GeoRuby & Spatial Adapter, I was doing this:

• Have two fields: one text field and a real geometry field, on the model

• On a after_save hook, I ran something like this:

  connection.execute "update mytable set geom_column=#{text_column} where id=#{id}"

But the solution above was just a hack, and this have additional issues: I can't create a spatial index if the column allows NULL values, MySQL doesn't let me set a default value on a geometry column, and the save method fails if the geometry column doesn't have a value set.

So I would try GeoRuby & Spatial Adapter instead, or reuse some of its code (on my case, I am considering extracting only the GIS-aware MysqlAdapter#quote method from the Spatial Adapter code).