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News routing devise rails
[rails routing] protecting a mounted engine

In a project we built, we are using que for doing our background-jobs, and there is a very simple (but sufficient) and clean web-ui, called que-web, allowing us to monitor the status of the jobs online.

And normally, you just include it in your project by adding the gem, and then adding the following to your config/routes.rb :

require "que/web"
mount Que::Web => "/que"

But, this is completely open and unauthenticated. So we use devise, and it is really easy to limit a route to authenticated users:

require "que/web"
authenticate :user do 
  mount Que::Web => "/que"
end

At least this limits the accessability to logged in users. But we wanted it to be available only to admin-users. So I thought I had to resort to defining my own constraint-class, as follows

class CanSeeQueConstraint
  def matches?(request)
    # determine if current user is allowed to see que
  end
end

and in the routes write it as follows

require 'can_see_que_constraint'
mount Que::Web, at: '/que', constraints: CanSeeQueConstraint.new

The problem was: how do I get to the current user, in a constraint class? So I took a peek at how the authenticate block in devise works, and apparently there is an easier option: the authenticate block takes a lambda, where you can test the currently authenticated user. Woah! Just what we need. So we wrote the following to only allow our adminstrators to see/manage our background jobs:

authenticate :user, lambda {|u| u.roles.include?("admin") } do
  mount Que::Web, at: 'que'
end
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Technology ruby ruby on rails render_anywhere
Using render-anywhere gem with partials

Normally in rails, you can only render views inside of the controller. But what if you want to render a view somewhere else? For instance we wanted to generate xml-files using views. Haml can be used to describe xml just as well as plain html.

There is a gem called render_anywhere that allows just that. So how does this work, for example:

class Organisation < ActiveRecord::Base

  has_many :members

  include RenderAnywhere

  def to_xml
    render partial: "#{self.to_partial_path}", object: self, layout: 'my_xml_layout'
  end
end

We had a little problem when using partials though.

Normally if you type something like

= render @member

it will ask the partial path from the model (@member.to_partial_path), but somehow this always got prefixed with render_anywhere. The gem creates a dummy RenderingController in the RenderAnywhere namespace, so apparently it will look for the following view:

render_anywhere/members/member

In our case, I did not want to use the render_anywhere subfolder. It took me a while to figure out how to overrule this, but in essence it is pretty simple: rails uses the namespace of the rendering controller to prefix the path. Some deep googling proved that any controller has a method called _prefixes which lists all the prefixes for that class.

We can easily verify this in the rails console:

:001 > RenderAnywhere::RenderingController._prefixes
=> ["render_anywhere/rendering"]

So if we could overrule _prefixes to just return ["rendering"] ... Mmmmmm fork the code of render_anywhere? Or ...

There is another option: render_anywhere allows you to supply your own RenderingController and will use that instead if found in the context where the RenderAnywhere code is included.

So, if you write something like:

class Organisation < ActiveRecord::Base

  has_many :members

  include RenderAnywhere

  class RenderingController < RenderAnywhere::RenderingController

    def self._prefixes
      ["rendering"]
    end

  end

  def to_xml
    render partial: "#{self.to_partial_path}", object: self, layout: 'my_xml_layout'
  end
end

it will look for a view called members/member. Woot. To specify a different sub-folder you can adapt the _prefixes method as you wish :)

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News ruby on rails schema_plus postgis
[rails] ignoring specific postgis view and tables in schema.rb

Developing rails websites with a geographic component we rely heavily on Postgis, so we use activerecord-postgis-adapter for the Postgis support, and I always use schema_plus because it allows me to define views. Until recently, I always had to use the structure.sql instead of the schema.rb because the geometric columns did not dump correctly.

But for a while now, activerecord-postgis-adapter handles this correctly and so we use the schema.rb file again. Only to discover a "new" error:

ActiveRecord::StatementInvalid: PG::DependentObjectsStillExist: ERROR: cannot drop view geography_columns because extension postgis requires it
HINT: You can drop extension postgis instead.
: DROP VIEW IF EXISTS "geography_columns"

Apparently specific Postgis views are also dumped in the schema file, and those views obviously cannot simply be re-created.

A very naive solution I kept using was to comment those create_view lines in our schema.rb file. But apparently there is a much better solution: you can configure which tables and views schema_plus should ignore.

So I added an initializer in /initializers/schema_dumper.rb with the following content:

ActiveRecord::SchemaDumper.ignore_tables = [
   "geography_columns", "geometry_columns", "spatial_ref_sys", "raster_columns", "raster_overviews"
]

And now my schema.rb is correct, and simple commands as rake db:setup or rake db:test:prepare just work. Hehe.

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News geoserver oracle
[geoserver] failed to look up primary key in oracle table

I have a very weird problem with my geoserver+oracle, when deployed on a Windows 2012R2 server (see here), and in attempting to solve that, I upgraded the geoserver from 2.6.3 to 2.7.1, hoping that that would fix that.

Sometimes fairy tales come true, but in this case it did not help, unfortunately. The 2.7.1 did render a lot quicker, except one layer which did not render at all anymore.

My style could not render with the error The requested Style can not be used with this layer. The style specifies an attribute of <missing attribute name>. Checking the layer in geoserver, I could see it was no longer to determine any of the attributes for the given table.

Further investigation in the logfile revealed the following (cryptic) error:

Failure occurred while looking up the primary key with finder: org.geotools.jdbc.HeuristicPrimaryKeyFinder@24cf7139

java.sql.SQLException: Exhausted Resultset

Mmmmmm. Luckily my google-fu revealed a linked issue, and simple solution:

update the driver from ojdbc14.jar to the newer ojdbc7.jar fixes this problem.

Hehe :)

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News geoserver oracle
[geoserver] having duplicate columns in your oracle based layer

Updating geoserver did not fix my problem: my layer still had some duplicate columnnames. This might not be such a big problem: everything is drawn correctly, WMS calls work, but WFS calls gave the irritating yet predictable error ORA-00918: column ambiguously defined. Annoying.

So how does one find column-names for a table in oracle? With a query like:

select * from dba_tab_columns where table_name = 'YOUR_TABLE_NAME';

and all of a sudden I saw the same set of column-names, with some duplication. Apparently my oracle database contains the table twice, in two different schema's. Since my user had the permissions to access the other schema, it seems geoserver does not limit the query to the (specified) schema at all.

The fix then was easy: make the other schema unaccessible. In my case the second schema was for testing purposes, so I could just delete it.

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News
Upgrading my local geoserver instance from 2.3.3 to 2.6.3

At my current job, we make GIS websites, using rails and geoserver. I develop on mac, and for some clients we need to deploy on windows. One client is still using an Oracle database, while in general I prefer to work with postgis databases, and also geoserver offers better support when using postgis.

So: when working locally I got a really weird phenomenon in my geoserver: it duplicated various oracle columns. Generally, for viewing not a problem but when using WFS I got the "column ambigously defined", and using Oracle SQL Views did not work (it went looking for meta data?) and the Geoserver SQL Views were painfully slow.

But on my clients server I installed Geoserver 2.6.3 and the oracle stuff just worked. Woot :) So I had to upgrade my ancient 2.3.3 geoserver. It is running inside a tomcat. Upgrading seemed easy enough: copy the old geoserver folder somewhere (actually you would only need the data folder and the web.xml but I am lazy/extra safe like that), and drop the new war, and theoretically, we should be good to go.

Except ... I got this peculiar error in my log-file

SEVERE: Error listenerStart

WTF! Thanks to some googling, I added a file logging.properties to my geoserver\WEB-INF\classes with the following content:

org.apache.catalina.core.ContainerBase.[Catalina].level = DEBUG
org.apache.catalina.core.ContainerBase.[Catalina].handlers = java.util.logging.ConsoleHandler

restarted my tomcat, and the following appeared:

SEVERE: Error configuring application listener of class org.geoserver.platform.GeoServerHttpSessionListenerProxy
java.lang.UnsupportedClassVersionError: org/geoserver/platform/GeoServerHttpSessionListenerProxy : Unsupported major.minor version 51.0 (unable to load class org.geoserver.platform.GeoServerHttpSessionListenerProxy)

Now what the hell cryptic error is that? But apparently this is a very compact way to say this code needs java 1.7 and I am still using java 1.6 (I am looking at you Apple). Updating now :)

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News ruby on rails
[rails] select distinct values of a column

The simplest way to select all distinct values of a column is, somewhat unintuitively:

Visit.uniq.pluck(:project)

this runs the query select distinct project from visits, and returns an array of strings. Exactly what you need, except ... I want it to be paginated. So we

Visit.uniq.pluck(:project).page(1)

... and that completely bombs: we now get an array of numbers?

So we try something else, and write:

Visit.select('distinct project')

which runs the good query, but returns an array of Visit's with only the project filled in. I can live with that. And then pagination (using the kaminari gem) is again as expected:

Visit.select('distinct project').page(params[:page])

Nice :)

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