do not override existing market records

apps/explorer/lib/explorer/market/market.ex

@@ -45,7 +45,7 @@ defmodule Explorer.Market do
         Decimal.equal?(item.closing_price, 0) && Decimal.equal?(item.opening_price, 0)
       end)
 
-    Repo.insert_all(MarketHistory, records_without_zeroes, on_conflict: :replace_all, conflict_target: [:date])
+    Repo.insert_all(MarketHistory, records_without_zeroes, on_conflict: :nothing, conflict_target: [:date])
   end
 
   def add_price(%{symbol: symbol} = token) do

apps/explorer/test/explorer/market/market_test.exs

@@ -91,9 +91,11 @@ defmodule Explorer.MarketTest do
       assert fetched_record.opening_price == old_record.opening_price
     end
 
-    test "overrides existing records on date conflict" do
+    test "does not override existing records on date conflict" do
       date = ~D[2018-04-01]
-      Repo.insert(%MarketHistory{date: date})
+
+      {:ok, old_record} =
+        Repo.insert(%MarketHistory{date: date, closing_price: Decimal.new(2), opening_price: Decimal.new(2)})
 
       new_record = %{
         date: date,
@@ -104,8 +106,8 @@ defmodule Explorer.MarketTest do
       Market.bulk_insert_history([new_record])
 
       fetched_record = Repo.get_by(MarketHistory, date: date)
-      assert fetched_record.closing_price == new_record.closing_price
+      assert fetched_record.closing_price == old_record.closing_price
-      assert fetched_record.opening_price == new_record.opening_price
+      assert fetched_record.opening_price == old_record.opening_price
     end
   end
 end