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Access Rails routes helpers outside the controllers e.g. in Models

Problem: The routes helper methods are available in views and controller as they are most of the time needed for displaying links in views or redirecting to other paths. But in one case I was expiring a page cache on an after_create callback of a model, for which I needed to access the path generated for that controller#action.

Solution: The RoutSet instance which contains all the helper methods is part of the Rails::Application object, and can be accessed at Rails.application.routes. You can access any URL helpers as follows:

Rails.application.routes.url_helpers.notification_path(notification) Rails.application.routes.url_helpers.notifications_path

#JustMigrated #Rails #Rails 3 #routes #url_helpers

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Use spork for multiple projects at the same time

Problem: If you use spork on your rails or ruby projects, and you are working on multiple projects at the same time, I am sure you have run into issues where Spork process of one project is causing other project builds to fail. You always need to remember to terminate the already running spork processes before you start working on other projects. How do you get rid of this nusance?

Solution:The spork process by default runs on port 8989, and any process which wants to fork from it will access it over the same port. We can simply change the port on which the process runs and configure rspec to access it over the same port.

I am using rspec with rails projects, so I am sharing what I have done on these projects. Add following configuration to .rspec file.

--drb --drb-port 9001

Now we will create an executable which you can use to start the spork process with particular port. Create a file RAILS_ROOT/script/spork containing following code

#!/usr/bin/env sh spork -p 9001

Make the file executable by chmod +x script/spork, and you are good to go. Always start the spork process using this executable and enjoy a hassle free spork benift.

#JustMigrated #Rails #RSpec #Spork #TDD

Rails ActiveResource HTTP_AUTHORIZATION headers

prblm: ActiveResource in Rails does not allow to add request headers, which is a general way to send authentication information. How to add custom headers to every request sent using ActiveResource?

solution: The ActiveResource has a very poorely written API, which does not provide any hook to provide custom headers to be added. We need to metaprogram our way around it as follows.

Add an entry to application.rb to load all files from app/extensions.

Create a module CustomAuthHeaders and include it in ActiveResource::Base

In the created module override headers method so that, when any request is made from ActiveResource::Base, custom request headers will be added.

https://gist.github.com/1100092

You can copy paste the above mentioned code in respective locations and all of ActiveResource requests will have extra headers as returned by AppAuthHeaders.headers

#JustMigrated #ActiveResource #authorization #custom headers #HTTP_AUTHORIZATION #Rails #request headers

Linux startup script seems not to have access to user environment

prblm: I was trying to configure a debian server, and the configuration script was suppose to run every time server boots up. The obvious thing to do would be to write a script and add it to rc.local. I was assuming that the script would be run as root user, and was using path and environment available to root user. But it nothing seemed to work, and on enabling boot logging, I figure out it could not find binaries in path.

solution: I am still not sure if the scripts executed at boot sequence are executed as root user with limited environment or they are executed as System user. But none the less, execute your commands as stated below

su -u root -l -c "<command>"

This will execute the command you want to execute as the root user, with his own environment as if he is logged in while executing the command. This comes in handy when lot of tools like svn, git manages authentication using files stored in user home directory, also there are certain path elements which are just too much to setup again.

#JustMigrated #boot #init #rc.local #Server

FactoryBean returned null object: not fully initialized due to circular bean reference

prblm: There are two beans in Spring container, which have dependency on each other. Thus while creating the beans, container cannot create any of the bean successfully. solution: There is only one elegant solution where, you mention dependency in a single bean configuration. This will avoid the circular referencing and to complete the bean initialization use a BeanPostProcessor, which would complete the initialization of the second bean. I found the code sample in this discussion thread at the bottom.

#JustMigrated #circular referencing #dev #spring

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How to support old urls, when changing the URL structures

prblm: We were performing a major restructuring of our URLs to make them more seo friendly. And in the process there were a lot of backend changes, which would make supporting the old URLs impossible. Also keeping both the code bases for URL supports was insanity. solution: One of our brilliant developers Avlesh came up with an approach of using url rewriter for converting old urls into new urls. Ours being a java based app, we were already using UrlRewriteFilter. If you are using apache, you could go along with mod_rewrite. Make sure that the old urls get permanently redirected (HTTP 301) to the new URLs. Permanently redirecting a url will suggest search engines that they need to stop service the old URL for any search request, and the new URL takes over the legacy of old one.

#JustMigrated

Hibernate commits happen in a particular order only

prblm: Using hibernate to persist data. There are two operations happening simultaneously, one insert and one update. The update is ordered first in the code and then insert. The inserts for certain reasons depend on update happening first. But when code is executed, it appears that insert happens before update. solution: Will explain why, but the only solution is to flush session after update and then execute the insert command. description: Search for "The SQL statements are issued in the following order" without quote on this hibernate documentation. Just for the lazy folks, here is what it says. The SQL statements are issued in the following order

all entity insertions, in the same order the corresponding objects were saved using ISession.Save()

all entity updates

all collection deletions

all collection element deletions, updates and insertions

all collection insertions

all entity deletions, in the same order the corresponding objects were deleted using ISession.Delete()

(An exception is that objects using native ID generation are inserted when they are saved.) Except when you explicity Flush(), there are absolutely no guarantees about when the Session executes the JDBC calls, only the order in which they are executed.

#JustMigrated #flush #Hibernate #transaction

Not able to ping localhost on Ubuntu

prblm: I was not able to ping localhost on Ubuntu, but I can access external sites without any problem. None of the services hosted and accessed from localhost are working. solution: The issue is due to the loopback interface not being properly configured. When system boots, it configures network interfaces as per configuration in file "/etc/network/interfaces". localhost is identified and pingable if interface lo (loopback) is configured. Make sure that following entry is present in the interfaces file -- auto lo iface lo inet loopback After saving the file execute "sudo /etc/init.d/networking restart". This will reload the configuration. Execute "ifconfig lo" to check if you get inet addr:127.0.0.1

#JustMigrated #localhost #network #ping #ubuntu

java.sql.Date(epoch) with SimpleDateFormat doesn't show time details

prblm: I created java.sql.Date object by providing epoch to it and when I format using SimpleDateFormat time factor was missing in the output. solution: Actually it was my mistake that I used the sql Date object, assuming that as it inherits java.util.Date the object behavior would remain same (how foolish of me to expect correct inheritance implementation). The sql Date tries to imitate database Date object where it does not contain time details. So the solution is to create java.util.Date always with SimpleDateFormat rather than java.sql.Date.

#JustMigrated

Rerouting http application request within different applications

prblm: My application uses a third party http request which doesn't support authentication, whereas I want the authentication to be done for my particular application. Another scenario is a client is to make an ajax request to an application which is not exposed over the net, and the other server is to server requests coming from provate IPs only. solution:Accept a URL in your appplication with all the parameters requred and in URL rewrite itself, reroute it to internal IP address with the request parameters as it is.

#JustMigrated

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hibernate does not consider aliases when executing native SQL query

prblm: I am executing a native SQL query on MySQL with aliases, which I expect hibernate would use to fetch data out of resultset while transforming it into an object. But it throws SQLException due to column being fetched not found. It seems that hibernate is calling getXXX using the actual column name rather than alias. solution:While creating connection using jdbc, use useOldAliasMetadataBehavior=true description: As per JDBC specification result set interface should provide two methods getColumnName and getColumnLabel. But old MySQL JConnector versions provide only getColumnName method and which returns the column alias (or label). In Certain release (dont remember which one) they started providing both methods, but to keep backward compatibility they introduced a parameter "useOldAliasMetadataBehavior" which would make getColumnName return alias and all the existing applications would still work. Till JConnector release 5.1 default value for this option was true, thus we never faced the heat. When I upgrade to 5.1.x, default value has been set to false and hibernate still thinks that MySQL JConnector would return alias on getColumnName method call. The only work around till hibernates dialect incorporates this behavior it to explicitly setting option "useOldAliasMetadataBehavior=true".

#JustMigrated #dev #Hibernate #JConnector #MySQL

MySQL foreign key constraint fails even when data is correct

prblm: I have a parent child table pair, and trying to insert data into child table which exists in parent table. The datatype and length of field etc etc is exactly same. But still MySQL throws constriant violation error. solution:Its not a universal solution as such, but please check if the constriant was created properly. If at the time of constraint creation FOREIGN_KEY_CHECKS was set to 0/false; the constraint definition would be stored in information_schema without evaluating if the table/column/schema names used even exists. description:Though at first glance the behavior of not checking the schema name looks sinister, the very flag FOREIGN_KEY_CHECKS tells MySQL that constriants are not to be checked. This would simple use the table/constraint creation script to dump the definition in information_schema and would be used to evaluate the constraint when activated. And as the MySQL error descriptions are as bad as they can be, whatever failure happens with data insertion in case of constraint evaluation is coined as constriant failure.

#JustMigrated #constraint #foreign key #MySQL

Javascript execute a function using its name as String literal

prblm: I have a function name passed on to me as string variable, and I have to execute the function. solutiong: There are two ways we can do it.

eval('function_name'+'()');

window['function_name']();

description: There isn't much to discuss about eval way. Its a standard javascript function which can be used to execute javascript code which is in string form. Its perfect to construct method call and execute it. The second interesting part is using window as array of objects. Window is a very high level object and all the functions, objects and variables defined at global level are stored with it as if its an array. These objects (function is an object) can be referred by their names as keys. Back to basics of javascript: Everything in javascript is finally stored as an array.

#JustMigrated #function #javascript #js

Trac entity views on multiple channels on web medium

prblm: On sites where various establishments (hotels, shops) are displayed, and can be passed on by users by means of various mediums; how to trac number of views of a particular establishment? Solution:

log the occurance of request in Action (on application logic side)

use a beacon request with parameters, whose request parameters can be logged at server side and then used to generate the statistics.

Description We chose the second approach. There is a common javascript function, which would accumulate data about all the entities to be logged. Taglibs in JSP would insert appropriate js called, which would populate a global JS map with the data. On page load, this js map would be serialized in request parameter format and a request is made to lighttpd server. This server would log the reqeust parameters in some delimited format; from where the log file would be dumped into mysql DB. Cron jobs would process this daily data and generate daily, weekly and monthly statistics Google analytics can provide you only those links where were clicked, but tracking if the user interaction on JS calls is not possible with it. Also if we just want to trac which all components were viewed by user, this is a really good way of doing it.

#JustMigrated

Apache commons fileupload 1.0, OutOfMemory with large number of form parameters

prbml: While using a multipart form, with large number of parameters, without large files, gets OutOfMemory Error. library:apache commons fileupload 1.0 solution:upgrade to Apache commons fileupload 1.2 or higher we were using apache commons fileupload library version 1.0 with struts 1.2. Struts uses this library internally to understand multipart form data and construct a complete file from request. Unfortunately the form interpriter with fileupload 1.0, treats all form parameters as files and tries to allocate default 256k memory each param. This was working perfectly fine when we had limited number of parameters, and we never felt the heat. But on one wicked day we were to use 2500 text parameters (all file inputs disabled, so no files included) to be sent across; and the request thread crashed with OutOfMemory error. Just upgraded fileupload lib to 1.2 or newer and we were able to test the same form with 10000 parameters successfully.

#JustMigrated #Bugs #fileupload #HTTP #multipart form #OutOfMemory

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java.sql.SQLException: ResultSet is from UPDATE. No Data.

MySQL ConnectorJ bug 25009. Fixed in 5.0.5 release. You can get this exception, also when trying to execute SQL query which is preceded by '--' (I know its weird!). We had this exception in our project when our .sql file execution util was neglecting the commented lines, starting with '--'.

#JustMigrated #25009 #Bugs #connectorj #MySQL #sql

svn: Network connection closed unexpectedly

trying to connect to svn with svn+ssh protocall. The user is not able to connect with ssh.

check the SSH serve. If its working properly, and the port you are using is correct (default 22)

check /var/log/auth.log - search for user name, you would find the error message there.

#JustMigrated #ssh #svn

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