Building Event Sourced Apps

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My Example

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Every team plays every other team twice 306 Matches

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Home Team Away Team +3 +0 +1 +1

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Transformation Input Output ?

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https://www.kaggle.com/mkhvalchik/soccer/data

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Match Team1 Team2 League SoSo Soccer

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sum(m.away_team_points) as points from (select *, case when away_team_goal > home_team_goal then 3 when home_team_goal = away_team_goal then 1 else 0 end as away_team_points, case when away_team_goal > home_team_goal then 1 else 0 end as away_team_wins, case when away_team_goal = home_team_goal then 1 else 0 end as away_team_draws, case when away_team_goal < home_team_goal then 1 else 0 end as away_team_losses from matches) m join leagues l on m.league_id = l.id group by season, away_team_api_id) t join leagues l on t.league_id = l.id join teams te on te.api_id = t.team_id group by (t.team_id, t.season) order by points desc, goal_difference desc, goals_for desc;

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def standings(season, league_id) Repo.all(m in Match, where: m.season == ^season and m.league_id == ^league_id) |> Map.merge(%{row.home_team_api_id => home_team_values(row) }, &add_up/3) |> Map.merge(%{row.away_team_api_id => away_team_values(row) }, &add_up/3) |> Enum.sort_by(fn s -> {s.points, s.goal_difference, s.goals_for} end, &>=/2) end defp home_team_values(row) do %{ games: 1, wins: Rules.wins(row.home_team_goal, row.away_team_goal), draws: Rules.draws(row.home_team_goal, row.away_team_goal), losses: Rules.losses(row.home_team_goal, row.away_team_goal), goals_for: row.home_team_goal, goals_against: row.away_team_goal, points: Rules.points(row.home_team_goal, row.away_team_goal) } end defp add_up(_k, nil, v2), do: v2 defp add_up(_k, v1, v2) when is_integer(v1), do: v1 + v2 defp add_up(_k, v1, v2) when is_map(v1), do: Map.merge(v1, v2, &add_up/3)

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Problem?

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Simplicity?

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Performance?

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Change!

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T1 T2 T3

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There are only two hard things in Computer Science …

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Rethink

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It’s a Tool

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It’s a Tool that helps you capture stuff that happened

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MatchStarted MatchStarted MatchStarted TeamFounded TeamFounded TeamFounded TeamFounded TeamFounded TeamQualified TeamQualified TeamQualified MachEnded MachEnded MachEnded SeasonEnded SeasonStarted

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project %TeamQualifiedForSeason{} = qualified do Ecto.Multi.insert(multi, :standings, %Standing{ season_id: qualified.season_id, team_api_id: qualified.team_api_id, team_long_name: qualified.team_long_name, league_id: qualified.league_id, sort_key: sort_key(0, 0, 0) }) end project %MatchEnded{} = ended do season_id = id_from_stream_id(ended.season_id) home_team = Standing.by_team_and_season(ended.home_team_api_id, season_id) away_team = Standing.by_team_and_season(ended.away_team_api_id, season_id) home_team_diff = team_changeset(home_team, ended.home_team_goal, ended.away_team_goal) away_team_diff = team_changeset(away_team, ended.away_team_goal, ended.home_team_goal) multi |> Ecto.Multi.update(:home_team, home_team_changeset) |> Ecto.Multi.update(:away_team, away_team_changeset) end

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(Re)Tell (Re)Tell (Re)Tell Capture https://github.com/leifg/so_so_soccer

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It’s a Tool that helps you capture events …

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… and tell a story from them

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“But I don’t like Football”

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Let’s get some Calories

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Demo Time

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TrackMeal Meal MealTracked Command Aggregate Event ?

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/api/do_stuff Command

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/meals TrackMeal Frontend MealTracked Phx Channel

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Hacker News Vanity

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HnStory •StorySubmitted •StoryVotedOn •StoryHitFrontPage •StoryFrontPagePositionChanged

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Offer Price: £1000 Buyer: E-Corp Status: “accepted” SELECT SUM(price) FROM offers WHERE status = ‘accepted’ GROUP BY buyer_id; Offer Price: £1000 Buyer: E-Corp Status: “paid” SELECT SUM(price) FROM offers WHERE status in (‘accepted’, ‘paid’) GROUP BY buyer_id;

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Offer Price: £1000 Buyer: E-Corp Status: “accepted” SELECT SUM(price) FROM offers WHERE status = ‘accepted’ GROUP BY buyer_id; Offer Price: £1000 Buyer: E-Corp Status: “rejected”

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Event Sourcing is Great for Side Projects It’s also Great for Real World Applications leif.io If you know the business bit.ly/buildingconduit