#check for column
ActiveRecord::Base.connection.tables.include?(name)

#check for table
Model.columns_hash.has_key("column_name")?

Migrations as version control for databases

When I first learned about Rails migration, I immediately thought that dropping down a revision would be something you would do often. In actuality, Rails migrations is more like a version control for databases. Since databases changes require modifications to both code and data, you cannot simply use a source code version control system like Subversion or Sourcesafe. You need a more advanced revisioning system for databases… hence Rails Migrations.

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