add csharp-es sample
This commit is contained in:
Oli Sturm
@@ -0,0 +1,93 @@
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using CsharpEs.Library;
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namespace CsharpEs.Domain;
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public sealed record AccountState(Guid Id);
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public abstract record AccountCommand
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{
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public sealed record OpenAccount(Guid AccountId, Money OpeningBalance) : AccountCommand;
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public sealed record WithdrawMoney(Guid AccountId, Money Amount) : AccountCommand;
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public sealed record DepositMoney(Guid AccountId, Money Amount) : AccountCommand;
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}
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public abstract record AccountEvent(Guid AccountId)
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{
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public sealed record AccountOpened(Guid AccountId, Money OpeningBalance)
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: AccountEvent(AccountId);
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public sealed record MoneyWithdrawn(Guid AccountId, Money Amount) : AccountEvent(AccountId);
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public sealed record MoneyDeposited(Guid AccountId, Money Amount) : AccountEvent(AccountId);
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}
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public abstract record AccountError
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{
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public sealed record AccountNotFound : AccountError;
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public sealed record AccountOpenAlready : AccountError;
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public sealed record OpeningBalanceMustBeNonNegative : AccountError;
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public sealed record InnerException(Exception exception) : AccountError;
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}
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public static class AccountDecider
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{
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public static Result<AccountEvent, AccountError> Decide(
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AccountState? state,
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AccountCommand command
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) =>
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Result<AccountEvent, AccountError>.Catch(
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() =>
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(state, command) switch
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{
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// if this is a new account, check for valid opening balance
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(null, AccountCommand.OpenAccount c) when c.OpeningBalance.Amount < 0m =>
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Result<AccountEvent, AccountError>.Fail(
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new AccountError.OpeningBalanceMustBeNonNegative()
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),
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// still a new account, now we can open it
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(null, AccountCommand.OpenAccount c) => Result<AccountEvent, AccountError>.Ok(
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new AccountEvent.AccountOpened(c.AccountId, c.OpeningBalance)
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),
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// if we have an account already, you can't open it
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(not null, AccountCommand.OpenAccount c) => Result<
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AccountEvent,
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AccountError
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>.Fail(new AccountError.AccountOpenAlready()),
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(null, _) => Result<AccountEvent, AccountError>.Fail(
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new AccountError.AccountNotFound()
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),
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(_, AccountCommand.WithdrawMoney c) => Result<AccountEvent, AccountError>.Ok(
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new AccountEvent.MoneyWithdrawn(c.AccountId, c.Amount)
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),
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(_, AccountCommand.DepositMoney c) => Result<AccountEvent, AccountError>.Ok(
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new AccountEvent.MoneyDeposited(c.AccountId, c.Amount)
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),
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_ => throw new InvalidOperationException("Unknown command."),
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},
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e => new AccountError.InnerException(e)
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);
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public static Result<AccountState?, AccountError> Evolve(
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AccountState? state,
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AccountEvent @event
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) =>
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(state, @event) switch
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{
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(null, AccountEvent.AccountOpened e) => Result<AccountState?, AccountError>.Ok(
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new AccountState(e.AccountId)
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),
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_ => Result<AccountState?, AccountError>.Ok(state),
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};
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}
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@@ -0,0 +1,3 @@
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namespace CsharpEs.Domain;
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public sealed record Money(decimal Amount);
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@@ -0,0 +1,108 @@
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using System.Collections.Immutable;
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using CsharpEs.Domain;
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using CsharpEs.Library;
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namespace CsharpEs.Infrastructure;
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public abstract record ReadModelError
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{
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public sealed record AccountDetailsNotFound : ReadModelError;
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}
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public sealed record AccountBalanceReadModel(
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Func<AccountEvent, Result<AccountDetails, ReadModelError>> Project,
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Func<Result<KeyValuePair<Guid, AccountDetails>[], ReadModelError>> Query
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);
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[Flags]
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public enum AccountFlags
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{
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None = 0,
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InOverdraft = 1,
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}
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public sealed record AccountDetails(Money Balance, AccountFlags Flags);
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public static class AccountBalanceReadModelModule
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{
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public static Result<AccountBalanceReadModel, ReadModelError> Create()
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{
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// This is our read-model specific "persistent" storage
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var modelData = ImmutableDictionary<Guid, AccountDetails>.Empty;
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Result<AccountDetails, ReadModelError> Project(AccountEvent @event)
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{
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Logging.Output("rm", "Projecting event", @event);
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switch (@event)
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{
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case AccountEvent.AccountOpened e:
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modelData = modelData.SetItem(
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e.AccountId,
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new AccountDetails(e.OpeningBalance, AccountFlags.None)
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);
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break;
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case AccountEvent.MoneyWithdrawn e:
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{
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if (modelData.TryGetValue(e.AccountId, out var oldDetails))
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{
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var newBalance = new Money(oldDetails.Balance.Amount - e.Amount.Amount);
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modelData = modelData.SetItem(
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e.AccountId,
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oldDetails with
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{
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Balance = newBalance,
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Flags = CalcAccountFlags(newBalance, oldDetails),
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}
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);
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}
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else
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return Result<AccountDetails, ReadModelError>.Fail(
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new ReadModelError.AccountDetailsNotFound()
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);
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}
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break;
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case AccountEvent.MoneyDeposited e:
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{
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if (modelData.TryGetValue(e.AccountId, out var oldDetails))
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{
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var newBalance = new Money(oldDetails.Balance.Amount + e.Amount.Amount);
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modelData = modelData.SetItem(
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e.AccountId,
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oldDetails with
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{
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Balance = newBalance,
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Flags = CalcAccountFlags(newBalance, oldDetails),
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}
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);
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}
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else
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return Result<AccountDetails, ReadModelError>.Fail(
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new ReadModelError.AccountDetailsNotFound()
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);
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}
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break;
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}
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// Read model-side "project" may not normally return any data, but for demo
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// purposes we return the affected data directly to save us modeling a separate
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// query side.
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return Result<AccountDetails, ReadModelError>.Ok(modelData[@event.AccountId]);
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}
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Result<KeyValuePair<Guid, AccountDetails>[], ReadModelError> Query() =>
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Result<KeyValuePair<Guid, AccountDetails>[], ReadModelError>.Ok(modelData.ToArray());
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return Result<AccountBalanceReadModel, ReadModelError>.Ok(
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new AccountBalanceReadModel(Project, Query)
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);
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}
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private static AccountFlags CalcAccountFlags(Money newBalance, AccountDetails oldDetails)
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{
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return newBalance.Amount < 0
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? oldDetails.Flags | AccountFlags.InOverdraft
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: oldDetails.Flags & ~AccountFlags.InOverdraft;
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}
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}
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@@ -0,0 +1,59 @@
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using System.Text.Json;
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using System.Text.Json.Serialization;
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namespace CsharpEs.Library;
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public static class Logging
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{
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public static T LogReturn<T>(string message, T r)
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{
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Console.WriteLine(message);
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return r;
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}
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static string Indent(string text, int indent = 4)
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{
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var prefix = new string(' ', indent);
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return Environment.NewLine
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+ string.Join(
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Environment.NewLine,
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text.Split(Environment.NewLine).Select(line => prefix + line)
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);
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}
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public static string Format(Object? o) =>
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o != null
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? Indent(
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JsonSerializer.Serialize(
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o,
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new JsonSerializerOptions
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{
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WriteIndented = true,
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Converters = { new JsonStringEnumConverter() },
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}
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)
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)
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: "(null)";
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public static void Output(string src, string message, Object? x)
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{
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Console.WriteLine($"[{src}] {message} | {Format(x)}");
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}
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public static void Output(string src, string message)
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{
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Console.WriteLine($"[{src}] {message}");
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}
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public static Action<T> OutputDelegate<T>(string src, string message) =>
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x =>
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{
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Output(src, message, x);
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};
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public static void OutputError<T>(string src, T error)
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{
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Console.Error.WriteLine($"\e[1;31m[{src} ERROR]\e[0m {Format(error)}");
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}
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}
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@@ -0,0 +1,138 @@
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namespace CsharpEs.Library;
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public readonly record struct Result<T, E>
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{
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private readonly T _value;
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private readonly E _error;
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public bool IsSuccess { get; }
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public bool IsFailure => !IsSuccess;
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public T Value =>
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IsSuccess
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? _value
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: throw new InvalidOperationException("No value present for failed result.");
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public E Error =>
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IsFailure
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? _error
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: throw new InvalidOperationException("No error present for successful result.");
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private Result(T value)
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{
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_value = value;
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_error = default!;
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IsSuccess = true;
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}
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private Result(E error)
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{
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_value = default!;
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_error = error;
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IsSuccess = false;
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}
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public static Result<T, E> Ok(T value) => new(value);
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public static Result<T, E> Fail(E error) => new(error);
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public TResult Match<TResult>(Func<T, TResult> onSuccess, Func<E, TResult> onFailure) =>
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IsSuccess ? onSuccess(_value) : onFailure(_error);
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public void Switch(Action<T> onSuccess, Action<E> onFailure)
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{
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if (IsSuccess)
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onSuccess(_value);
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else
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onFailure(_error);
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}
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public static Result<T, E> Catch(Func<T> f, Func<Exception, E> exceptionMapper)
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{
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try
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{
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var result = f();
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return Result<T, E>.Ok(result);
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}
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catch (Exception e)
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{
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return Result<T, E>.Fail(exceptionMapper(e));
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}
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}
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public static Result<T, E> Catch(Func<Result<T, E>> f, Func<Exception, E> exceptionMapper)
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{
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try
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{
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return f();
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}
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catch (Exception e)
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{
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return Result<T, E>.Fail(exceptionMapper(e));
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}
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}
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}
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public static class ResultExtensions
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{
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public static Result<TOut, E> Bind<TIn, TOut, E>(
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this Result<TIn, E> result,
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Func<TIn, Result<TOut, E>> binder
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) => result.IsSuccess ? binder(result.Value) : Result<TOut, E>.Fail(result.Error);
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public static Result<TOut, E> Map<TIn, TOut, E>(
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this Result<TIn, E> result,
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Func<TIn, TOut> mapper
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) =>
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result.IsSuccess
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? Result<TOut, E>.Ok(mapper(result.Value))
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: Result<TOut, E>.Fail(result.Error);
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public static Result<T, E> Tap<T, E>(this Result<T, E> result, Action<T> action)
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{
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if (result.IsSuccess)
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action(result.Value);
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return result;
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}
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public static Result<T, E> TapError<T, E>(this Result<T, E> result, Action<E> action)
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{
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if (result.IsFailure)
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action(result.Error);
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return result;
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}
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public static Result<T, EOut> MapError<T, EIn, EOut>(
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this Result<T, EIn> result,
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Func<EIn, EOut> map
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) =>
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result.IsSuccess
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? Result<T, EOut>.Ok(result.Value)
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: Result<T, EOut>.Fail(map(result.Error));
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public static Result<T, E> Log<T, E>(this Result<T, E> result, string src, string msg) =>
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Tap(result, Logging.OutputDelegate<T>(src, msg)).TapError(m => Logging.OutputError(src, m));
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public static Result<T, E> Log<T, E>(
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this Result<T, E> result,
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string src,
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Func<T, string> renderText
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) =>
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Tap(result, x => Logging.OutputDelegate<T>(src, renderText(x))(x))
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.TapError(m => Logging.OutputError(src, m));
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public static Result<TOut, E> Select<TIn, TOut, E>(
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this Result<TIn, E> result,
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Func<TIn, TOut> mapper
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) => result.Map(mapper);
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public static Result<TOut, E> SelectMany<TIn, TIntermediate, TOut, E>(
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this Result<TIn, E> result,
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Func<TIn, Result<TIntermediate, E>> binder,
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Func<TIn, TIntermediate, TOut> projector
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) => result.Bind(x => binder(x).Map(y => projector(x, y)));
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}
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@@ -0,0 +1,84 @@
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using System.Collections.Immutable;
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using CsharpEs.Domain;
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using CsharpEs.Infrastructure;
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using CsharpEs.Library;
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public abstract record DemoError
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{
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public sealed record Account(AccountError Error) : DemoError;
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public sealed record ReadModel(ReadModelError Error) : DemoError;
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}
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public class Program
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{
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private static Guid accountId;
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private static ImmutableList<AccountCommand> demoCommands = ImmutableList<AccountCommand>.Empty;
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static Program()
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{
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accountId = Guid.NewGuid();
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demoCommands = demoCommands.AddRange([
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new AccountCommand.OpenAccount(accountId, new Money(-200m)),
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// new AccountCommand.OpenAccount(accountId, new Money(200m)),
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new AccountCommand.WithdrawMoney(accountId, new Money(100m)),
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new AccountCommand.WithdrawMoney(accountId, new Money(200m)),
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new AccountCommand.DepositMoney(accountId, new Money(500m)),
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]);
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}
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static ImmutableList<AccountEvent> eventStore = ImmutableList<AccountEvent>.Empty;
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static Result<AccountState?, DemoError> ApplyEvent(
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AccountBalanceReadModel balanceProjection,
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AccountState? state,
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AccountEvent @event
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)
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{
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eventStore = eventStore.Add(@event);
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Logging.Output(
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"ae",
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$"Applying event {Logging.Format(@event)} to state {Logging.Format(state)}"
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);
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return AccountDecider
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.Evolve(state, @event)
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.MapError(e => (DemoError)new DemoError.Account(e))
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.Bind(newState =>
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balanceProjection
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.Project(@event)
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.MapError(e => (DemoError)new DemoError.ReadModel(e))
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.Log("ae ad", "Account details")
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.Map(_ => newState)
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)
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.Log("ae", $"Applied and projected {Logging.Format(@event)}");
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}
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public static void Main(string[] args)
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{
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Logging.Output("csharp-es", "Starting money handling demo...");
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AccountBalanceReadModelModule
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.Create()
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.MapError(e => (DemoError)new DemoError.ReadModel(e))
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.Bind(readModel =>
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demoCommands
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.Aggregate(
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Result<AccountState?, DemoError>.Ok(null),
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(stateResult, command) =>
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stateResult.Bind(state =>
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AccountDecider
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.Decide(state, command)
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.MapError(e => (DemoError)new DemoError.Account(e))
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.Bind(@event => ApplyEvent(readModel, state, @event))
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)
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)
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.Bind(s =>
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readModel
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.Query()
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.Log("query", "Read model data")
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.MapError(e => (DemoError)new DemoError.ReadModel(e))
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)
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)
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.Log("csharp-es done", "Demo completed.");
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}
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}
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@@ -0,0 +1,9 @@
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<Project Sdk="Microsoft.NET.Sdk">
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<PropertyGroup>
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<OutputType>Exe</OutputType>
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<TargetFramework>net10.0</TargetFramework>
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<RootNamespace>CsharpEs</RootNamespace>
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<ImplicitUsings>enable</ImplicitUsings>
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<Nullable>enable</Nullable>
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</PropertyGroup>
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</Project>
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Reference in New Issue
Block a user