VRFS-1664 added paging to fetc_recipients

ruby/lib/jam_ruby/models/email_batch_new_musician.rb

@@ -60,7 +60,7 @@ SQL
       ActiveRecord::Base.connection.execute(sql)
     end
 
-    def fetch_recipients
+    def fetch_recipients(per_page=500)
       objs = []
       # load new musicians into tmp table
       self._fetch_new_musicians
@@ -68,20 +68,27 @@ SQL
       # load email receivers into tmp table
       self._fetch_eligible_receivers
 
-      sql = "SELECT DISTINCT receiver_id FROM #{TMP_PAIRS} GROUP BY receiver_id"
-      ActiveRecord::Base.connection.execute(sql).each do |result|
-        receiver = User.find_by_id(result['receiver_id'])
-
-        sql = "SELECT new_user_id, latency FROM #{TMP_PAIRS} WHERE receiver_id = '#{receiver.id}'"
-        new_musicians = ActiveRecord::Base.connection.execute(sql).collect do |rr| 
-          new_user = User.where(['id = ?',rr['new_user_id']])
-            .limit(1)
-            .includes([:instruments])
-            .first
-          new_user.latency_store = result['latency']
-          new_user
+      countsql = "SELECT DISTINCT COUNT(receiver_id) AS num FROM #{TMP_PAIRS} GROUP BY receiver_id"
+      num_pair = ActiveRecord::Base.connection.execute(countsql)[0]['num'].to_i
+      loops = (num_pair / per_page) + (num_pair % per_page) - 1
+      0.upto(loops) do |nn|
+        offset = nn * per_page
+        sql =<<SQL
+SELECT DISTINCT receiver_id 
+FROM #{TMP_PAIRS} 
+GROUP BY receiver_id
+ORDER BY receiver_id ASC
+LIMIT #{per_page}
+OFFSET #{offset}
+SQL
+        ActiveRecord::Base.connection.execute(sql).each do |result|
+          receiver = User.find_by_id(result['receiver_id'])
+          new_musicians = User.select("users.*, #{TMP_PAIRS}.latency")
+            .joins("INNER JOIN #{TMP_PAIRS} ON #{TMP_PAIRS}.new_user_id = users.id")
+            .where(["#{TMP_PAIRS}.receiver_id = ?", receiver.id])
+            .includes(:instruments)
+          block_given? ? yield(receiver, new_musicians) : objs << [receiver, new_musicians]
         end
-        block_given? ? yield(receiver, new_musicians) : objs << [receiver, new_musicians]
       end
       objs
     end