Fix breakdown API pagination when using event metrics

CHANGELOG.md

@@ -4,6 +4,7 @@ All notable changes to this project will be documented in this file.
 ## Unreleased
 
 ### Fixed
+- Fix breakdown API pagination when using event metrics plausible/analytics#2562
 - Automatically update all visible dashboard reports in the realtime view
 
 ### Changed

lib/plausible/stats/breakdown.ex

@@ -223,7 +223,7 @@ defmodule Plausible.Stats.Breakdown do
 
   defp breakdown_events(site, query, property, metrics, pagination) do
     from(e in base_event_query(site, query),
-      order_by: [desc: fragment("uniq(?)", e.user_id)],
+      order_by: [desc: fragment("uniq(?)", e.user_id), asc: fragment("min(?)", e.timestamp)],
       select: %{}
     )
     |> do_group_by(property)

test/plausible_web/controllers/api/external_stats_controller/breakdown_test.exs

@@ -1588,6 +1588,47 @@ defmodule PlausibleWeb.Api.ExternalStatsController.BreakdownTest do
       assert Enum.count(res["results"]) == 2
     end
 
+    test "does not repeat results", %{conn: conn, site: site} do
+      populate_stats([
+        build(:pageview, %{domain: site.domain, "meta.key": ["item"], "meta.value": ["apple"]}),
+        build(:pageview, %{domain: site.domain, "meta.key": ["item"], "meta.value": ["kiwi"]}),
+        build(:pageview, %{domain: site.domain, "meta.key": ["item"], "meta.value": ["kiwi"]}),
+        build(:pageview, %{domain: site.domain, "meta.key": ["item"], "meta.value": ["pineapple"]}),
+        build(:pageview, %{domain: site.domain, "meta.key": ["item"], "meta.value": ["pineapple"]}),
+        build(:pageview, %{domain: site.domain, "meta.key": ["item"], "meta.value": ["pineapple"]}),
+        build(:pageview, %{domain: site.domain, "meta.key": ["item"], "meta.value": ["grapes"]}),
+        build(:pageview, %{domain: site.domain, "meta.key": ["item"], "meta.value": ["grapes"]}),
+        build(:pageview, %{domain: site.domain, "meta.key": ["item"], "meta.value": ["grapes"]}),
+        build(:pageview, %{domain: site.domain, "meta.key": ["item"], "meta.value": ["grapes"]})
+      ])
+
+      params = %{
+        "site_id" => site.domain,
+        "metrics" => "visitors",
+        "property" => "event:props:item",
+        "limit" => 3,
+        "page" => nil
+      }
+
+      first_page =
+        conn
+        |> get("/api/v1/stats/breakdown", %{params | "page" => 1})
+        |> json_response(200)
+        |> Map.get("results")
+        |> Enum.map(& &1["item"])
+        |> MapSet.new()
+
+      second_page =
+        conn
+        |> get("/api/v1/stats/breakdown", %{params | "page" => 2})
+        |> json_response(200)
+        |> Map.get("results")
+        |> Enum.map(& &1["item"])
+        |> MapSet.new()
+
+      assert first_page |> MapSet.intersection(second_page) |> Enum.empty?()
+    end
+
     @invalid_limit_message "Please provide limit as a number between 1 and 1000."
 
     test "returns error when limit too large", %{conn: conn, site: site} do