A modern, cache-efficient Entity Component System (ECS) for games, simulations, and other data-oriented workloads. EntitiesDb focuses on raw performance, simple APIs, and zero external dependencies — all in pure C#.

using var db = new EntityDatabase();

var player = db.Create(new Position(0, 0), new Velocity(1, 1));

var query = db.QueryBuilder.WithAll<Position, Velocity>().Build();

query.ForEach((ref Position pos, in Velocity vel) =>
{
    pos.X += vel.Dx;
    pos.Y += vel.Dy;
});

• 🚀 Fast — archetype-organized, fixed-size chunk storage; components of a type are contiguous in memory
• 🧩 Simple — any struct/class/record is a component; expressive WithAll / WithAny / WithNone / WithOnly queries
• ⚙️ Source-generated ForEach — lambdas with ref/in parameters are rewritten at compile time into strongly-typed loops; the generator ships inside the package, no setup
• 🧵 Multithreaded — ForEachParallel / ForEachChunkParallel with a single fork/join per query, plus per-thread aggregates for reductions (opt-in via options)
• 📦 Tags & inline buffers — zero-size tag components and [Buffer(n)] inline lists stored directly in the chunk
• 🔍 Change filters — only visit chunks whose components were written since the last pass
• 🧮 SIMD-friendly — reinterpret component handles as Vector128/256/512<T> and process several entities per instruction
• 📝 Command buffers — thread-safe deferred Create / Add / Set / Remove / Destroy, applied with one Commit()
• 🔧 Manual enumeration — walk archetypes, chunks and raw read/write handles when you need full control
• 0️⃣ GC-friendly — unmanaged chunk memory, allocation-free iteration, no per-entity objects
• 🎯 Targets net8.0 and netstandard2.1 — no dependencies on .NET 8 (System.Memory + System.Runtime.CompilerServices.Unsafe on netstandard)

dotnet add package EntitiesDb

<PackageReference Include="EntitiesDb" Version="*" />

Install-Package EntitiesDb

• Runtime: .NET 8+ or any runtime that supports netstandard2.1 (Unity, Mono, .NET Core 3.x, …)
• SDK: the ForEach source generator needs a Roslyn 4.3+ compiler — .NET 6 SDK or newer, or a recent Visual Studio / Rider
• Language: lambdas with ref / in parameters (C# 7.2+); the samples below use record struct (C# 10)

Consuming the project instead of the package? Reference the generator too, so ForEach gets rewritten:

<ProjectReference Include="..\EntitiesDb\EntitiesDb.csproj" />
<ProjectReference Include="..\EntitiesDb.SourceGenerators\EntitiesDb.SourceGenerators.csproj"
                  OutputItemType="Analyzer" ReferenceOutputAssembly="false" />

Without the generator, ForEach throws CodeGenerationException at runtime.

using EntitiesDb;

// 1. Define components — plain types, no base class or interface
public record struct Position(float X, float Y);
public record struct Velocity(float Dx, float Dy);
public record struct Health(int Points, int Max);

// 2. Create a database (defaults: 16 KB chunks, unlimited entities, parallel disabled)
using var db = new EntityDatabase();

// 3. Create entities (up to 16 components per call)
var player = db.Create(new Position(10, 10), new Velocity(5, 5), new Health(100, 100));
var rock   = db.Create(new Position(0, 0));

// 4. Work with a single entity
db.Add(rock, new Velocity(1, 0));
db.Has<Velocity>(rock);                             // true
ref var hp = ref db.Write<Health>(player);          // by-ref write
hp.Points -= 10;
ref readonly var pos = ref db.Read<Position>(rock); // by-ref read
db.Remove<Velocity>(rock);
db.Destroy(rock);

// 5. Build a query once, reuse it every frame
var movers = db.QueryBuilder
    .WithAll<Position, Velocity>()
    .Build();

// 6. Iterate — `ref` = write, `in` = read
movers.ForEach((ref Position pos, in Velocity vel) =>
{
    pos.X += vel.Dx;
    pos.Y += vel.Dy;
});

Each snippet is a taste — follow the links for the full story in DOCS.md.

var query = db.QueryBuilder
    .WithAll<Damage, EnemyTag>()   // must have all
    .WithAny<PlayerTag, NpcTag>()  // at least one of
    .WithNone<BossTag>()           // none of
    .Build();

var exact = db.QueryBuilder.WithOnly<Position, Velocity>().Build(); // exactly these

→ QueryBuilder

[Tag] public struct EnemyTag { }                       // zero-size marker
[Buffer(8)] public record struct Item(int Id, int Count); // inline list, 8 elements in-chunk

var e = db.Create(new Position(1, 1), new EnemyTag(), new[] { new Item(1, 5) });

var items = db.WriteBuffer<Item>(e);
items.Add(new Item(2, 1));

→ Buffers · Tags

query.ForEachChunk((int len, WriteHandle<Position> pos, ReadHandle<Velocity> vel) =>
{
    var p = pos.Reinterpret<Position, Vector256<float>>(); // 4 entities per lane (2 floats each)
    var v = vel.Reinterpret<Velocity, Vector256<float>>();
    int simdLen = (len - (len & 3)) / 4;
    for (int i = 0; i < simdLen; i++) p[i] += v[i];
    for (int i = simdLen * 4; i < len; i++) { pos[i].X += vel[i].Dx; pos[i].Y += vel[i].Dy; }
});

→ ForEachChunk · SIMD

// parallel execution is opt-in — physical cores are the sweet spot (see Benchmarks)
using var db = new EntityDatabase(new EntityDatabaseOptions(parallelThreads: Environment.ProcessorCount / 2));

query.ForEachParallel((ref Position pos, in Velocity vel) => { pos.X += vel.Dx; pos.Y += vel.Dy; });

// per-thread state + join for reductions (SumAggregate : IParallelAggregate<int>)
var total = new SumAggregate();
query.ForEachParallel((in Wallet w, ref int local) => local += w.Gold, ref total);

No structural changes (Create/Add/Remove/Destroy) inside parallel loops — use a command buffer.

→ Multithreading · Parallel Aggregate

[TrackChanges] public record struct Position(float X, float Y);

var moved = db.QueryBuilder
    .WithAll<Position, Renderable>()
    .WithChangeFilter<Position>()   // only chunks where Position was written since last pass
    .Build();

→ Change Filter

var commands = db.CreateCommandBuffer(initialCapacity: 256);

query.ForEachParallel((Entity e, in Health hp) =>
{
    if (hp.Points <= 0) commands.Destroy(e);   // thread-safe
});

commands.Commit();                              // apply on the main thread

→ Command Buffers

foreach (var (length, positions, velocities) in query.WriteHandles<Position, Velocity>())
    for (int i = 0; i < length; i++) { positions[i].X += velocities[i].Dx; }

→ Manual Enumeration

• An entity is an int id plus a version; ids are recycled and the version rejects stale handles.
• Entities with the same set of components share an archetype. Each archetype owns a list of fixed-size chunks (16 KB by default, EntityDatabaseOptions.chunkByteSize) laid out structure-of-arrays: all Positions in a chunk are contiguous, then all Velocitys, and so on.
• Unmanaged components live in unmanaged chunk memory (no GC tracking); class components are supported through parallel managed arrays but iterate slower.
• A query is a signature filter that lazily matches archetypes; iterating it means walking matched chunks and handing out spans (ReadHandle<T> / WriteHandle<T>).
• ForEach lambdas are captured by a Roslyn incremental source generator that emits a strongly-typed extension method per call site — no delegate invocation or boxing per entity. The generator is packaged as an analyzer inside the NuGet package.
• Parallel methods run one fork/join per call over a fixed thread pool; threads claim batches of chunks from a shared cursor (dynamic scheduling, so a preempted thread can't stall the join) and per-thread state is created and joined through IParallelAggregate<T>. Steady-state parallel calls don't allocate.
• Structural changes (create/destroy/add/remove) move entities between archetypes and are single-threaded; a thread-safe CommandBuffer defers them.
• Limits: 256 component types per process, 16 components per Create/Add call, component size ≤ 32 KB.

Numbers from the in-repo BenchmarkDotNet suite, which compares EntitiesDb against plain List<struct> / List<class> loops doing the same work. Snapshot: 2026-08-17, EntitiesDb 3.6.1, Intel Core i7-8700K (6C/12T), Windows 11, .NET 8.0.27 x64, library-default options (16 KB chunks), parallel rows on 12 threads. Full reports with mean/error/std-dev columns: src/EntitiesDb.Benchmark/results/2026-08-17-v3.6.1.

c1.Value += c2.Value over every entity — SystemWithTwoComponents (single archetype), median time per pass:

Same work, entities spread over 4 archetypes — SystemWithTwoComponentsVariedComposition (median):

Parallel — ParallelScaling, same c1 += c2 work, parallelThreads = 6 (physical cores), median per pass:

Parallel calls allocate nothing in steady state. Threads claim chunks from a shared cursor (guided self-scheduling), so a preempted thread only delays its current batch. Thread count matters: with 11–12 threads on this 6-core/12-thread CPU the same calls were 2–5× slower and highly variable (SMT siblings add nothing to memory-bound loops, and using every logical processor oversubscribes the box) — use physical cores.

Create 100 000 entities with one component — CreateEntityWithOneComponent (mean; managed allocations only ‡):

Notes:

• EntitiesDb_ForEach is the like-for-like row (a scalar per-entity loop, same as the baselines). *_Simd rows are hand-vectorized; a SIMD baseline over SoA arrays is on the follow-up list.
• Medians are shown throughout; the machine was not isolated.
• ‡ BenchmarkDotNet's Allocated column counts managed heap only. EntitiesDb stores entities and unmanaged components in native chunk memory, which is not included — the 84 KB is entity-map growth, not total memory.
• Entity creation is a structural change and is not EntitiesDb's design center; the numbers are here for completeness. The command-buffer path trades throughput for thread-safety and deferral.
• All timings are one machine on one day. Reproduce with dotnet run -c Release --project src/EntitiesDb.Benchmark.

📚 Full guide: DOCS.md

Core Concepts · EntityDatabase · Entities · Components · Buffers · Tags · Queries · ForEach · ForEachChunk · Change Filter · Manual Enumeration · Multithreading · Parallel Aggregate · Command Buffers · SIMD · Attributes

git clone https://github.com/Juiix/EntitiesDb.git
cd EntitiesDb

dotnet build src/EntitiesDb.sln -c Release
dotnet test  src/EntitiesDb.Tests
dotnet run   -c Release --project src/EntitiesDb.Benchmark      # optional, slow

Repository layout:

Editing a .tt template requires re-running the T4 generator (Visual Studio does this on save; the generated .cs files are checked in).

Issues and pull requests are welcome. Please run dotnet test src/EntitiesDb.Tests before opening a PR, and include a benchmark run for performance-sensitive changes.

MIT — free for commercial and open-source use.