Arel is now bundled in the Active Record gem, and maintained in the rails/rails repository.
Arel Really Exasperates Logicians Arel is a SQL AST manager for Ruby. It 1. Simplifies the generation of complex SQL queries 2. Adapts to various RDBMSes It is intended to be a framework framework; that is, you can build your own ORM with it, focusing on innovative object and collection modeling as opposed to database compatibility and query generation.
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gem install arel -v 9.0.0
Arel is now bundled in the Active Record gem, and maintained in the rails/rails repository.