Identifying Duplicate Records in Phoenix Applications Using Ecto

This article discusses a common maintenance task in Phoenix applications: detecting duplicate records. It explains a method to identify duplicates in a table called 'tags' that includes fields such as id, name, and a scoping column named scope_id. The process involves grouping records by name and scope_id, filtering out groups with more than one occurrence, and then joining those groups back to the original table to retrieve all duplicates. The article also provides Ecto code snippets for creating grouped subqueries and retrieving full records of duplicate entries. The use of schema modules is encouraged for more expressive Ecto queries. This pattern proves useful for not only reporting duplicates but also for cleanup tasks and background jobs in Phoenix applications.