I am trying to connect to a database from my rails app. This database is being updated all the time for storing the results of ongoing tests. My rails app is basically a front-end to display the test results.
What is the best way to access the sqlite database without interfering with the test framework? At the moment when I start the rails server it locks the database and no read/write is allowed to it while the server is running.
What is the best way to display results from a continuously growing database, where new records are not being added by the rails app itself? Thanks for your help!
You should consider using another database engine, such as MySQL or Postgres. SQLite is a good RDBMS but does not fit well for high-concurrency scenarios. It has been designed mainly for desktop or device-embedded applications.
From http://www.sqlite.org/whentouse.html
SQLite uses reader/writer locks on the entire database file. That
means if any process is reading from any part of the database, all
other processes are prevented from writing any other part of the
database. Similarly, if any one process is writing to the database,
all other processes are prevented from reading any other part of the
database.
Related
we have two databases in our project, one for primary and one for backup. Both of the databases have exactly same data.
we have used EF designer model to get SP's from db. we call any method by just using object.spName . This is working perfectly if we have only one db. But since we have multi db system i need to make sure that insertion operation works on both db and select queries can be run from primary only and backup will be used to get records only if primary is down.
What is the best approach to get this working, or how can i specify multiple db in same connection string
You don't want to do this on the application layer... You should look into database technologies like replication to perform this, or use native database backups and restore them on a schedule
Imagine an error occurs between the first and second, or someone does a manual query - your dbs will be out of sync.
Are there any good practice on how can we insert data into a Rails App's models from an external source (not the web app), while still leveraging the ORM capabilities of active record? How possible is it for the ActiveRecord class be imported into our own external ruby script without the complete rails package? I was hoping to avoid writing raw SQLs as much as possible. Thanks!
Sure you can.
One way would be to use rake tasks within your app, which can access your ActiveRecord models. It will still load your app up, but not as a web service.
http://jasonseifer.com/2010/04/06/rake-tutorial
Also recommend this for more bulk style insert/updates:
https://github.com/zdennis/activerecord-import
There are a number of questions here about adding columns to a model via rails migration files and a rake db:migrate.
In this case, however, the application is basically a CRUD on top of an existing SQL Server database that is generated by another application. That is, I don't control it. Those who do control the database have added several columns to a table.
What I need is for the Rails app to respect the changes made to the database without assuming it has full control over the table structures.
I've tried plugging the new fields into the model and controller files, but sql queries give TinyTDS errors saying the new fields don't exist. Queries by hand (via SQL Server Management Studio) work fine. What am I missing? Why doesn't Rails recognize the new fields when they appear in the table model?
UPDATE:
It turns out that the problem is more subtle than I though when asking the initial question. As background, this application is set up with two databases, one production, one development/test. They are both on the same SQL Server database server. What's actually happening with the missing columns is that the Rails app pulls from production no matter what environment I use. Even when I change both environments to use the same development database (in database.yml), the app continues to query the production database.
Perhaps this is a problem between Rails and SQL Server. I've cleared all caches and cleared all database connections, but it makes no difference. It seems that the Rails app is caching the database name and login info somewhere.
One day I'd like to get this fixed, but for now I'll simply move the development database to another server for testing.
ActiveRecord has a cache of the table fields. If you want to reset the cache for a model without restarting your application, you can do:
MyModel.reset_column_information
I have a Rails app and a Sinatra app, sharing the same database. The Sinatra app uses ActiveRecord.
Can I run migrations from within each app, as if they were in the same app? Will this cause any problems?
The schema.rb file in the Rails app tracks the current migration via
ActiveRecord::Schema.define(:version => 20121108154656) do
but, how does the Sinatra app know the current version the database?
Rails 3.2.2, Ruby 1.9.3.
The version column in the schema_migrations table equate to the time stamp on the front of the ruby migration file example: 20130322151805_create_customers.rb So if two ore more applications are contributing to the schema_migrations table roll backs will not be possible if rails can't find the down() method (because it will not find a migration file contained in another app ie db/migrate/...)
I have a current situation that is exactly this and I have opted to have a master ActiveRecord app that manages migration and data conversions as our database evolves. Keep in mind that part of the deal is to keep models up to date as well. This has been time consuming so we are considering breaking apart the DB in to business domains and providing APIs (JSON) to query support data for another application. This way each application manages it domain and is responsible for exposing data via API.
regards.
If you connect both applications to the same database you should be able to run migrations on it but I strongly suggest you use another option since you will almost surely hit a wall at one time or another:
split the database in two if possible with each application responsible for its own database /migrations.
have one application considered the "master" database and use another database for the data specific to the second application but make it connects to both database (each application still only apply migrations to one database)
If you need to share data between multiple applications another option is to implement a REST service in one and use it on the other, you can have a look at the grape gem for a simple way of doing so.
Edit: I realize I forgot to speak about the activerecord migration, there is no longer any "version" of the schema, what activerecord does is that it read all your migration filename, extract their identifier (the starting part) and check if they have already been applied so in theory you can run migrations from two applications on the same database provided they don't interfere.
But if both migrations act on the same tables you will almost certainly run into big troubles at one point.
I disagree with Schmurfy, even if his presented options are valid, its a bit of an overkill to share data through REST (granted, its pretty easy to implement with ruby / rails).
If your case is simple you could just use one database from both apps, and since you use AR in both of them you have no problems with versioning, AR takes care of that.
Also i dont know what happens if you run db:migrate from both apps simultaniously if you use a inferior dbms like mysql which does not allow DDL in a transaction, certainly nothing good..
Also it would bother me to look which app needs what column and not have the migrations in one place. You could use a shared repository to manage the migrations from both apps.
Rails migrations store current database version in schema_migrations table in the database. So both of your apps will be able to check the current version.
The version numbers are timestamps, so there shouldn't be any problem with duplicate values, as it'll be almost impossible to generate two migrations at the exact same millisecond. So you should be fine here.
The only problem I see is that when you rollback a migration in one app, it'll set the db to the previous known version and I'm not sure if it will pick the previous one from the db (which could be from the other app), or the number from the previous migration file. You may want to test that scenario to make sure.
I decided to put all migrations in the Rails app because:
Since there is only one database
Rails manages migrations
This has worked well.
This simplifies the system because all migrations are stored in one place. And, the Sinatra app doesn't need to know about them anyway.
So for a class I have to turn in my Rails application to my professor. What is the best way to make sure everything goes smoothly when he trys to start it up? Also, is there anyway I can freeze a database and send that with it so he has all of the data I have been using in the application?
Thanks a lot.
Depending on your needs, the SQLite3 database (used by default in Rails) is stored on the file system in the db directory of your Rails app. So, assuming your professor has the requirements to run Ruby on Rails, the application will start up with the data you've used.
My guess is you have hard coded connection strings in your rails application. Ask your professor what server he will be running it off of. At that point either change the strings to match or create a config file that is read in and can be edited (which is the better choice of the two). Most databases have export functionality which will allow you to export the current information within the database.