Data Gateway

A proof-of-concept MCP (Model Context Protocol) server built to explore how AI agents interact with structured data sources. The server exposes database query tools over two different transports, following the official MCP documentation.

Overview

This project demonstrates two ways to host an MCP server in .NET — one for remote/debugging scenarios and one for local client-launched workflows:

McpDataGateway/
├── Tools/       # MCP tool definitions — transport-agnostic
├── Host.Http/   # ASP.NET Core host using Streamable HTTP transport
└── Host.Stdio/  # Console host using stdio transport

The server is backed by a PostgreSQL database seeded with the Pagila sample dataset — a DVD rental store schema with films, actors, customers, rentals, and payments — providing a realistic dataset for demonstrating data retrieval tools.

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Running with Docker Compose

The quickest way to get the full stack running locally (MCP HTTP server + PostgreSQL + pgAdmin).

First-time setup

Note: If you have a leftover docker_local/postgresql/data directory from a previous run, delete it first so PostgreSQL re-initialises from the seed scripts:

# Windows
rmdir /s /q docker_local\postgresql\data

# macOS / Linux
rm -rf docker_local/postgresql/data

Start all services

docker-compose up -d

Service	Address
MCP HTTP server	http://localhost:5000
pgAdmin	http://localhost:5435
PostgreSQL (host access)	localhost:5434

Connecting pgAdmin to PostgreSQL

1. Open http://localhost:5435 and log in with:

   • Email: [email protected]
   • Password: postgres

2. Right-click Servers → Register → Server…

3. On the General tab, give it any name (e.g. mcp-postgres).

4. On the Connection tab, fill in:

   Field	Value
   Host	postgres
   Port	5432
   Maintenance DB	postgres
   Username	postgres
   Password	R0ck&R0ll

   Use postgres (the Docker container hostname) and port 5432. The localhost:5434 address is only for connections from outside Docker.

5. Click Save. The Pagila tables are visible under postgres → Schemas → public → Tables.

Stop all services

docker-compose down

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Running the HTTP Streamable host

Suitable for debugging, remote access, or connecting multiple clients simultaneously.

dotnet run --project McpDataGateway/Host.Http

The server starts on http://localhost:5000. Point your MCP client at:

{
  "mcpServers": {
    "mcp-data-gateway": {
      "url": "http://localhost:5000/mcp"
    }
  }
}

Debugging in Visual Studio: Set Host.Http as the startup project and press F5. You can place breakpoints anywhere in the Tools/ project and trigger them via tool calls from your MCP client.

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Running the stdio host

Suitable for local workflows where the MCP client spawns the server process directly.

dotnet run --project McpDataGateway/Host.Stdio

Configure your MCP client to launch the process:

{
  "mcpServers": {
    "mcp-data-gateway": {
      "command": "dotnet",
      "args": ["run", "--project", "path/to/McpDataGateway/Host.Stdio"]
    }
  }
}

Or point to the published executable after dotnet publish:

{
  "mcpServers": {
    "mcp-data-gateway": {
      "command": "path/to/Host.Stdio.exe"
    }
  }
}

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Choosing a transport

	HTTP Streamable (Host.Http)	stdio (Host.Stdio)
Breakpoint debugging	✅	❌
Multiple simultaneous clients	✅	❌
Remote / hosted deployment	✅	❌
MCP client manages the process	❌	✅
No separate server process needed	❌	✅

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Sample data

The PostgreSQL database is seeded with the Pagila sample database — an open-source PostgreSQL port of the Sakila MySQL example database, maintained by Devrim Gündüz.

Pagila is made available under the PostgreSQL License.

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References

• Model Context Protocol — Getting Started
• Pagila sample database