# Cosmos Provider

> Implementation details for the EF Core Azure Cosmos DB provider. Use when changing Cosmos-specific code.

- Skill: `dotnet/cosmos-provider` (Agent Skill)
- Install (CLI): `npx skillmds@latest add dotnet/cosmos-provider`
- Raw SKILL.md: https://api.skillmd.com/api/skills/dotnet/cosmos-provider/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: DevOps & Infra
- Author: .NET (Microsoft) (https://skillmd.com/u/dotnet)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/dotnet/cosmos-provider

---


# Cosmos DB Provider

Non-relational provider with its own parallel query pipeline. Uses JSON for document materialization.

## Key Differences from Relational

- No migrations — use `EnsureCreated()`
- Documents as JSON — owned and complex types become embedded objects
- Partition key configuration required for performance
- `ETag` for optimistic concurrency
- No cross-container joins

## Azure Cosmos DB Emulator for Tests

- `TestEnvironment.InitializeAsync()` auto-starts a `Testcontainers.CosmosDb` container when `Test__Cosmos__DefaultConnection` is not set. Set the env var to use an existing emulator instead.
- Skip tests requiring unsupported features on the Linux emulator with ` [ConditionalFact(typeof(CosmosTestEnvironment), nameof(CosmosTestEnvironment.IsNotLinuxEmulator))]`.