Add Validate Column Data With Check Constraints as a Rails TIL

rails/validate-column-data-with-check-constraints.md

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+# Validate Column Data With Check Constraints
+
+A check constraint is a feature of database systems like PostgreSQL that allows
+you to enforce rules about the data that goes in a table's column. As of Rails
+6.1, ActiveRecord provides a way to add a check constraint via the DSL.
+
+In this example, we want to ensure that the value going into the
+reading_statuses.status column is one of four values. Nothing else besides
+these four values should be allowed.
+
+```ruby
+class AddReadingStatusTable < ActiveRecord::Migration[7.2]
+  def change
+    create_table :reading_statuses do |t|
+      t.references :user, null: false, foreign_key: true
+      t.references :book, null: false, foreign_key: true
+      t.string :status, null: false
+      t.timestamps
+    end
+
+    add_check_constraint
+      :reading_statuses,
+      "status in ('started', 'completed', 'abandoned', 'already_read')",
+      name: "reading_statuses_valid_status_check"
+  end
+end
+```
+
+The `#add_check_constraint` method takes the name of the table and a SQL clause
+that can evaluate to true or false for a given row. We can optionally include
+the name of the check constraint (e.g. {table_name}_{column_name}_check) like
+we've done above.