Rails provides two methods that address this problem by dividing records into memory-friendly batches for processing.
To retrieve objects from the database, Active Record provides several finder methods.
Each finder method allows you to pass arguments into it to perform certain queries on your database without writing raw SQL.
@articles = current_user.visible_articles.where(name: params[:name]) def visible_articles case role when 'Country Manager' Article.where(country: country) when 'Reviewer' Article.published when 'Bad User' # = Optimistic locking allows multiple users to access the same record for edits, and assumes a minimum of conflicts with the data.
It does this by checking whether another process has made changes to a record since it was opened.
Note that you will see duplicate categories if more than one article has the same category.
If you want unique categories, you can use SELECT categories.* FROM categories INNER JOIN articles ON articles.category_id = INNER JOIN comments ON comments.article_id = INNER JOIN guests ON guests.comment_id = INNER JOIN tags ON tags.article_id = Or, in English: "return all categories that have articles, where those articles have a comment made by a guest, and where those articles also have a tag."You can specify conditions on the joined tables using the regular Array and String conditions.This is possible by specifying the This will find the category with id 1 and eager load all of the associated articles, the associated articles' tags and comments, and every comment's guest association.Even though Active Record lets you specify conditions on the eager loaded associations just like If an association is eager loaded as part of a join, any fields from a custom select clause will not present be on the loaded models.Code examples throughout this guide will refer to one or more of the following models: Active Record will perform queries on the database for you and is compatible with most database systems, including My SQL, Maria DB, Postgre SQL, and SQLite.Regardless of which database system you're using, the Active Record method format will always be the same.The methods are: in a single pass, build a model object per row, and then keep the entire array of model objects in memory.