.NET RAG with PostgreSQL pgvector + Aspire

A production-style Retrieval-Augmented Generation (RAG) implementation in .NET using PostgreSQL pgvector, .NET Aspire, and pluggable LLM providers (Ollama / OpenAI).

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Overview

This project demonstrates how to build a semantic search + RAG pipeline using modern .NET practices:

• Vector similarity search with pgvector
• LLM-based answer generation (Ollama / OpenAI)
• Clean Architecture (Domain, Application, Infrastructure)
• .NET Aspire orchestration (Postgres + Ollama + API)
• Provider-agnostic design (LLM + vector store)

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Architecture

User Query
   ↓
Embedding Service (Ollama / OpenAI)
   ↓
Vector Store (pgvector)
   ↓
Top-K Retrieved Documents
   ↓
LLM (RAG Prompt)
   ↓
Generated Answer

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Solution Structure

DotNetRagPgvector/
│
├── AppHost/                 # Aspire orchestration
├── Api/                     # Minimal API (entry point)
├── Application/             # Use cases + abstractions
│   ├── Abstractions/        # IEmbeddingService, IVectorStore, ILLMService
│   ├── Services/            # RagService, IngestionService
│   └── DTOs/                # UserInput
│
├── Domain/                  # Core models
│   └── Models/
│       ├── Document
│       └── RetrievedDocument
│
├── Infrastructure/          # Implementations
│   ├── Entities/            # EF Core Entities - DesignPatterns
│   ├── Persistence/         # EF Core + pgvector
│   ├── VectorStores/        # PgVectorStore
│   ├── Embeddings/          # Ollama / OpenAI
│   └── LLM/                 # Ollama / OpenAI

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Features

• ✅ Semantic search using embeddings
• ✅ Retrieval-Augmented Generation (RAG)
• ✅ pgvector integration with PostgreSQL
• ✅ Clean architecture with strict separation of concerns
• ✅ Pluggable LLM providers (Ollama / OpenAI)
• ✅ Aspire-based container orchestration
• ✅ Scalar UI for API testing

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Tech Stack

• .NET 10
• ASP.NET Core Minimal APIs
• Entity Framework Core
• PostgreSQL + pgvector
• .NET Aspire
• Ollama (local LLM)
• OpenAI (optional)

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Getting Started

1. Prerequisites

• .NET 10 SDK
• Docker Desktop (Or Podman - set Aspire container runtime to podman)
• .NET Aspire workload

dotnet workload install aspire

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2. Run the Application

dotnet run --project AppHost

This starts:

• PostgreSQL (pgvector)
• Ollama
• API

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3. Open API UI (Scalar)

Navigate to:

http://localhost:<api-port>/scalar

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Testing the API

POST /ask

{
  "query": "How to handle distributed transactions?"
}

Example Questions

• How to prevent cascading failures?
• How to scale read-heavy systems?
• How do microservices communicate asynchronously?

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Configuration

appsettings.json

{
  "AI": {
    "Provider": "Ollama",
    "Ollama": {
      "BaseUrl": "http://localhost:11434",
      "EmbeddingModel": "nomic-embed-text",
      "ChatModel": "phi4-mini"
    },
    "OpenAI": {
      "ApiKey": "",
      "EmbeddingModel": "text-embedding-3-small",
      "ChatModel": "gpt-4o-mini"
    }
  }
}

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Provider Switching

Switch between Ollama and OpenAI:

"Provider": "Ollama"
// or
"Provider": "OpenAI"

No code changes required.

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🗄️ Database & Vector Search

• Uses PostgreSQL with pgvector
• Embeddings stored as vector column
• Cosine similarity used for retrieval:

var results = await dbContext.DesignPatterns
    .OrderBy(x => x.Embedding.CosineDistance(questionVector))
    .Take(2)
    .ToListAsync();

ORDER BY "Embedding" <=> @queryVector
LIMIT 2

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Data Seeding

• Automatic on startup
• Uses real-world architecture patterns dataset
• Embeddings generated via selected provider

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RAG Flow (Code-Level)

// 1. Embed query
var queryEmbedding = await _embedding.GenerateAsync(query);

// 2. Retrieve relevant documents
var docs = await _vectorStore.SearchAsync(queryEmbedding);

// 3. Build prompt
// 4. Generate response using LLM

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Extensibility

You can easily extend:

Vector Stores

• pgvector ✅
• Pinecone (future)
• FAISS (future)

LLM Providers

• Ollama ✅
• OpenAI ✅
• Azure OpenAI (easy to add)

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Design Principles

• Domain is persistence-agnostic
• Infrastructure handles external dependencies
• Application orchestrates the RAG pipeline
• API acts as composition root

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Future Improvements

• Hybrid search (BM25 + vector)
• HNSW indexing for pgvector
• Streaming LLM responses
• Evaluation & benchmarking
• Metadata filtering

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Contributing

Contributions are welcome! Feel free to open issues or PRs.

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License

MIT License

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⭐ Why This Project?

This repository demonstrates a production-ready, provider-agnostic RAG architecture in .NET.

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Acknowledgements

• pgvector
• .NET Aspire
• Ollama