Our migration will then fail with an unintuitive error message: NoMethodError: undefined method `accessor' for #
Extra Tip 3: Migrating with Rails’ JSON Store The method you are calling in this migration might not run the same way, or exist anymore, which will prevent any new-comer to your project to run the migration set of the project smoothly. Using methods coming directly from your models can seem like a good idea at first to DRY your code, but with time and commits your model will change. If you need to use any kind of more advanced logic in your migration, define the methods you need in your migration and call them from there. ⚠️⚠️ Remember to only use raw Ruby+Rails logic in your migrations and never use anything except attributes coming from your own models. The migration should be one-way and not blindly set values back to nil in the down direction to avoid losing data if you were to roll it back.ĭepending on your project, you could merge both migrations into one. Gives: class RemoveNameFromMerchant 'active'}) The migration file generated will contain the following line: remove_column :table_name, :column_nameįor instance: $ rails generate migration RemoveNameFromMerchant name:string Rails automatically generates this kind of migrations thanks to the command line generator: $ rails generate migration RemoveFieldNameFromTableName field_name:datatype I’m starting with a basic that’s actually in the docs before getting to the tougher ones: 1- One line migration to drop DB columns: Retro-update existing records’ when adding a new column ★★★.So let’s walk through 9 tricks for generators and migrations gathered from experience (and Stack Overflow 🙊). At work at Forest Admin it’s our job to handle every possible DB schema, in Rails, NodeJS and others, which means we’ve come across a few variations already. But while the most common migrations are no-brainers, some of them are not -or not clearly- covered in the manual. Whenever you reference a column from another table in a condition or orderĬlause, ALWAYS use the table name to prefix the column, even if it notĪmbiguous among the tables involved.Rails Migrations were introduced to be a convenient way to alter the database in a structured and organized manner, and effectively bring great consistency over time on a project.Īs Ruby on Rails developers (I’m assuming you are too 😘), we should be pretty familiar with Rails Migrations and the Rails generator.
This will cause the duplicate rows to reappear. When you specify a “lumn” syntax within a :conditions= >įull query with the join because you are referencing columns from another Large set of records (more than a “page”), you may need to “force” Id’s to load, and avoiding the duplicate rows.ĭuplicates, but can incur more database overhead. After 2.1, the query is broken down andĮager-loaded using an additional query per association, passing the set of The join executes a large query and returned potentially duplicate recordsįor a one-to-many association. :include=> in your find method caused ActiveRecord to generate SQL using a join. Specifying :include no longer necessarily joins the association
Is finished we get the expected person.visits = 4. By locking the row, the second transaction has = 2, add 1 to it, and save, resulting in two saves of Lock: Imagine two concurrent transactions: each will read person.visits
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