Blueprint: Post state TPH persistence

Copy these files when an aggregate uses a discriminated union for lifecycle state. Replace Post / PostState with your aggregate names. See docs/conventions/backend/infrastructure-layer.md and docs/conventions/backend/query-read-strategy.md.

EF Core complex type inheritance is not available yet (dotnet/efcore#31250). Use TPH columns on the aggregate table and an interceptor until that ships.

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1. Shared column constants (Application.Read.Contracts)

namespace {ProjectName}.Application.Read.Contracts.Posts;

public static class PostStateColumns
{
    public const string StateType = "StateType";
    public const string PublishedAt = "PublishedAt";
    public const string ArchivedAt = "ArchivedAt";

    public const string Draft = "Draft";
    public const string Published = "Published";
    public const string Archived = "Archived";
}

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2. EF configuration (Infrastructure/Persistence/Configurations/PostConfiguration.cs)

internal sealed class PostConfiguration : IEntityTypeConfiguration<Post>
{
    public void Configure(EntityTypeBuilder<Post> builder)
    {
        builder.ToTable("posts");
        builder.HasKey(p => p.Id);

        builder.Ignore(p => p.State);

        builder.Property<string>(PostStateColumns.StateType)
            .HasColumnName("state_type")
            .HasMaxLength(20)
            .IsRequired()
            .HasDefaultValue(PostStateColumns.Draft);

        builder.Property<DateTimeOffset?>(PostStateColumns.PublishedAt)
            .HasColumnName("published_at");

        builder.Property<DateTimeOffset?>(PostStateColumns.ArchivedAt)
            .HasColumnName("archived_at");

        builder.HasIndex(PostStateColumns.StateType).HasDatabaseName("ix_posts_state_type");
        builder.HasIndex(PostStateColumns.PublishedAt).HasDatabaseName("ix_posts_published_at");
    }
}

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3. Interceptor (Infrastructure/Persistence/PostStatePersistence.cs)

Sync columns to State on materialization and State to columns before save. Use reflection to write the private State setter; do not add RehydrateState to Domain.

Register on DbContext options:

services.AddDbContext<AppDbContext>(options =>
    options
        .UseNpgsql(connectionString)
        .UseSnakeCaseNamingConvention()
        .AddInterceptors(new PostStatePersistenceInterceptor()));

See the LitePress reference implementation at apps/api/src/LitePress.Infrastructure/Persistence/PostStatePersistence.cs.

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4. Read-side query helpers (Application.Read)

internal static class PostStateQuery
{
    internal static IQueryable<Post> WherePublished(IQueryable<Post> query) =>
        query.Where(p => EF.Property<string>(p, PostStateColumns.StateType) == PostStateColumns.Published);

    internal static PostState FromColumns(
        string stateType,
        DateTimeOffset? publishedAt,
        DateTimeOffset? archivedAt) =>
        stateType switch
        {
            PostStateColumns.Draft => new DraftPostState(),
            PostStateColumns.Published when publishedAt.HasValue => new PublishedPostState(publishedAt.Value),
            PostStateColumns.Archived when archivedAt.HasValue => new ArchivedPostState(archivedAt.Value),
            _ => throw new InvalidOperationException($"Unknown post state discriminator '{stateType}'.")
        };
}

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5. Migration checkpoint

dotnet ef migrations add MUST produce:

• state_type varchar NOT NULL
• published_at timestamptz NULL
• archived_at timestamptz NULL
• indexes on state_type and published_at

MUST NOT produce a single jsonb state column unless a project ADR documents that deviation.