# database-performance

Enforces database access performance patterns for .NET, separating read and write models, banning in-memory joins, and preventing N+1 queries.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 664 installs · ★ 1238
- Author: Aaronontheweb
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/Aaronontheweb/dotnet-skills/tree/HEAD/skills/database-performance/SKILL.md
- Updated: 2026-10-11
- HTML: https://affpapa.org/en/nevibecode/skills/database-performance

## What it does

This skill guides agents in designing data access layers with EF Core and Dapper. It enforces a strict CQRS separation where read and write models never share types. Read operations return specialized, denormalized DTOs like `UserProfile` or `UserSummary`, while writes accept strongly typed commands such as `CreateUserCommand`.

The pattern establishes strict query limits. Every read method requires an explicit limit parameter with cursor or offset pagination, and table joins must happen in SQL rather than application code. For EF Core queries, it mandates `AsNoTracking()` because change tracking adds memory overhead to stateless reads.

Because the skill sets `user-invocable: false`, you do not invoke it with a slash command. The agent pulls these rules automatically when you ask it to optimize slow queries or write repository stores.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add Aaronontheweb/dotnet-skills --skill database-performance -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/database-performance/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/database-performance/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add Aaronontheweb/dotnet-skills --skill database-performance -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/database-performance/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add Aaronontheweb/dotnet-skills --skill database-performance -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/database-performance/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install Aaronontheweb/dotnet-skills database-performance
```

2. **Manually: put the files in place**
- File: `.github/skills/database-performance/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add Aaronontheweb/dotnet-skills --skill database-performance -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/Aaronontheweb/dotnet-skills --path skills/database-performance
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/database-performance/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add Aaronontheweb/dotnet-skills --skill database-performance -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/Aaronontheweb/dotnet-skills/tree/HEAD/skills/database-performance/SKILL.md

## When to use it
- separate read and write models using CQRS patterns
- disable costly EF Core change tracking on read queries
- eliminate N+1 queries by batching related data fetches
- enforce required row limits and cursor pagination on read methods
- keep data joins inside SQL rather than application memory

## Example prompts
- Design an order store interface in .NET separating read DTOs from write commands.
- Refactor this EF Core customer query to use AsNoTracking and cursor pagination.
- Review this Dapper query repository for N+1 performance issues.

## Source text · SKILL.md · MIT

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: 7f32d48a3b338781.

BEGIN THIRD-PARTY FILE 7f32d48a3b338781
````text
---
name: database-performance
description: Database access patterns for performance. Separate read/write models, avoid N+1 queries, use AsNoTracking, apply row limits, and never do application-side joins. Works with EF Core and Dapper.
user-invocable: false
tags: [cqrs, performance, patterns]
---

# Database Performance Patterns

## When to Use This Skill

Use this skill when:
- Designing data access layers
- Optimizing slow database queries
- Choosing between EF Core and Dapper
- Avoiding common performance pitfalls

---

## Core Principles

1. **Separate read and write models** - Don't use the same types for both
2. **Think in batches** - Avoid N+1 queries
3. **Only retrieve what you need** - No SELECT *
4. **Apply row limits** - Always have a configurable Take/Limit
5. **Do joins in SQL** - Never in application code
6. **AsNoTracking for reads** - EF Core change tracking is expensive

---

## Read/Write Model Separation (CQRS Pattern)

**Read and write models are fundamentally different - they have different shapes, columns, and purposes.** Don't create a single "User" entity and reuse it everywhere.

- **Read models** are denormalized, optimized for query efficiency, and return multiple projection types (UserProfile, UserSummary, UserDetailForAdmin)
- **Write models** are normalized, validation-focused, and accept strongly-typed commands (CreateUserCommand, UpdateUserCommand)

### Architecture

```
src/
  MyApp.Data/
    Users/
      # Read side - multiple optimized projections
      IUserReadStore.cs
      PostgresUserReadStore.cs

      # Write side - command handlers
      IUserWriteStore.cs
      PostgresUserWriteStore.cs

      # Read DTOs - lightweight, denormalized
      UserProfile.cs
      UserSummary.cs

      # Write commands - validation-focused
      CreateUserCommand.cs
      UpdateUserCommand.cs
    Orders/
      IOrderReadStore.cs
      IOrderWriteStore.cs
      (similar structure...)
```

### Read Store Interface

```csharp
// Read models: Multiple specialized projections optimized for different use cases
public interface IUserReadStore
{
    // Returns detailed profile for single-user view
    Task<UserProfile?> GetByIdAsync(UserId id, CancellationToken ct = default);

    // Returns lightweight info for lookups
    Task<UserProfile?> GetByEmailAsync(EmailAddress email, CancellationToken ct = default);

    // Returns paginated summaries - only what the list view needs
    Task<IReadOnlyList<UserSummary>> GetAllAsync(int limit, UserId? cursor = null, CancellationToken ct = default);

    // Boolean query - no entity needed
    Task<bool> EmailExistsAsync(EmailAddress email, CancellationToken ct = default);
}
```
````
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First 2683 of 14055 bytes. © Aaronontheweb · MIT · https://github.com/Aaronontheweb/dotnet-skills/tree/HEAD/skills/database-performance/SKILL.md

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