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Postgres H-Store

PostgreSQL is a powerful, open source object-relational database system based on POSTGRES, Version 4.2, developed at the University of California at Berkeley Computer Science Department. It is fully ACID(Atomicity, Consistency, Isolation, Durability) compliant,has full support for foreign keys, joins, views, triggers, and stored procedures (in multiple languages). It includes most SQL:2008 data types, including INTEGER, NUMERIC, BOOLEAN, CHAR, VARCHAR, DATE, INTERVAL, and TIMESTAMP. It also supports storage of binary large objects, including pictures, sounds, or video. It has native programming interfaces for C/C++, Java, .Net, Perl, Python, Ruby, Tcl, ODBC, among others, and exceptional documentation.

One of the great strengths of PostgreSQL is extensibility. Just as the JVM has become more than a way to just run Java—spawning languages such as Clojure and Scala—PostgreSQL has become more than just a home to relational data and the SQL language.HStore is a key value store within Postgres. You can use it similar to how you would use a dictionary within another language, though it’s specific to a column on a row.

Hstore is a schemaless key value column in Postgres. It's perfect if you need to store attributes for an object but aren't quite sure what your schema should be. Maybe we start selling 'Products' that have an author and an isbn, but then we want to start selling cameras, or computer equipment we'll need to store other things like amount of ram or manufacturer. With hstore, we can use the same column for both sets of data, no migrations or schema changes needed.Hstore is really useful for saving attributes on models. If you store settings for your users, you'd typically do this in a separate model (or on the User model). Each setting would be an additional column. Instead of adding columns each time you want to create a setting, you could instead use a single HStore column. It's much more flexible and doesn't require migrations each time we want to store something new.

hstore, enables you to build better apps faster without sacrificing the power, reliability, and flexibility of the underlying PostgreSQL storage engine. By using hstore, you will be able to leverage the flexibility and agility of schema-less data stores in existing environments. Although hstore is a mature, stable solution, it has recently been gathering widespread excitement

Support for hstore is available today in many popular languages and frameworks, including plugins for Django, Rails/ActiveRecord, Sequel, and Node.js. While you can be ahead of the curve now, hstore support will become a native part of ActiveRecord 4.

In Rails we can use hstore like a hash, you can input any key and any value you want. Once it's stored you can query the keys or values. If you've ever used a serialized hash column, hstore behaves much like that. The main difference is performance, since hstore is storing the keys and values natively in Postgres, queries run much much faster. Rails 4 supports the hstore column type, until then we'll need to use a gem.