Back fill started at

If the claim has a journey session we try and set the `started_at` to
that, if it doesn't have a journey session we'll just use the
`created_at` timestamp, which for claims pre the introduction of journey
sessions will be the started at time.

db/migrate/20240924095435_back_fill_claims_started_at.rb

@@ -0,0 +1,24 @@
+class BackFillClaimsStartedAt < ActiveRecord::Migration[7.0]
+  def up
+    execute <<-SQL
+      UPDATE claims
+      SET started_at = journeys_sessions.created_at
+      FROM journeys_sessions
+      WHERE claims.journeys_session_id = journeys_sessions.id
+      AND claims.started_at IS NULL
+    SQL
+
+    execute <<-SQL
+      UPDATE claims
+      SET started_at = created_at
+      WHERE journeys_session_id IS NULL
+      AND claims.started_at IS NULL
+    SQL
+
+    change_column_null :claims, :started_at, false
+  end
+
+  def down
+    Claim.update_all(started_at: nil)
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[7.0].define(version: 2024_09_24_091408) do
+ActiveRecord::Schema[7.0].define(version: 2024_09_24_095435) do
   # These are extensions that must be enabled in order to support this database
   enable_extension "citext"
   enable_extension "pg_trgm"
@@ -111,7 +111,7 @@
     t.text "onelogin_idv_first_name"
     t.text "onelogin_idv_last_name"
     t.date "onelogin_idv_date_of_birth"
-    t.datetime "started_at", precision: nil
+    t.datetime "started_at", precision: nil, null: false
     t.index ["academic_year"], name: "index_claims_on_academic_year"
     t.index ["created_at"], name: "index_claims_on_created_at"
     t.index ["eligibility_type", "eligibility_id"], name: "index_claims_on_eligibility_type_and_eligibility_id"