Improve example

docs/migrations.md

@@ -25,6 +25,18 @@ end
 This example shows a ticks table grouping ticks as OHLCV histograms for every
 minute.
 
+First make sure you have the model with the `acts_as_hypertable` method to be
+able to extract the query from it.
+
+```ruby
+class Tick < ActiveRecord::Base
+  self.table_name = 'ticks'
+  acts_as_hypertable
+end
+```
+
+Then, inside your migration:
+
 ```ruby
 hypertable_options = {
   time_column: 'created_at',
@@ -39,11 +51,6 @@ create_table :ticks, hypertable: hypertable_options, id: false do |t|
   t.integer :volume
   t.timestamps
 end
-Tick = Class.new(ActiveRecord::Base) do
-  self.table_name = 'ticks'
-  self.primary_key = 'symbol'
-  acts_as_hypertable
-end
 
 query = Tick.select(<<~QUERY)
   time_bucket('1m', created_at) as time,
@@ -79,7 +86,7 @@ function that can be reusing candlesticks from smaller timeframes.
     `disable_ddl_transaction!` in your migration file.
 
     ```ruby
-    class CreateTicks < ActiveRecord::Migration[6.0]
+    class CreateCaggsWithData < ActiveRecord::Migration[7.0]
       disable_ddl_transaction!
 
       def change