Chapter 4. ActiveRecord

ActiveRecord is a level of abstraction that offers access to a SQL database. ActiveRecord implements the architectural pattern Active Record [9].

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This is referred to as object-relational mapping, ORM. I find it rather dry and boring, but in case you have trouble going to sleep tonight, have a look at http://en.wikipedia.org/wiki/Object_relational_mapping.
One of the recipes for the success of Rails is surely the fact that is uses ActiveRecord. The programming and use feels Ruby like and it is much less susceptible to errors than pure SQL. When working with this chapter, it helps if you have some knowledge of SQL, but this is not required and also not essential for working with ActiveRecord.
Just as an aside, let me mention that you are not obliged to work with ActiveRecord when working with Rails. You can also use other ORMs. ActiveRecord is the default and is used by the majority of all Rails developers.