azure-cosmos-rust

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• SKILL.md

SKILL.md (first lines)

# Azure Cosmos DB library for Rust

Client library for Azure Cosmos DB NoSQL API — document CRUD, containers, and globally distributed data.

Use this skill when:

- An app needs to store or query documents in Cosmos DB from Rust
- You need CRUD operations on items with partition keys
- You need key-based auth as an alternative to Entra ID

> **IMPORTANT:** Only use the official `azure_data_cosmos` crate published by the [azure-sdk](https://crates.io/users/azure-sdk) crates.io user. Do NOT use the unofficial `azure_cosmos` or `azure_sdk_for_rust` community crates. Official crates use underscores in names and none have version 0.21.0.

## Installation

```sh
cargo add azure_data_cosmos azure_identity serde serde_json tokio
```

> If your code uses `azure_core` types directly (for example, `azure_core::credentials::TokenCredential`), add `azure_core` to `Cargo.toml`. If you only use `azure_data_cosmos` re-exports, direct `azure_core` dependency is optional.

## Environment Variables

```bash
COSMOS_ENDPOINT=https://<account>.documents.azure.com/ # Required for all operations
```

## Authentication

Rust Azure SDK code must not use `DefaultAzureCredential`. The Rust identity crate does not provide that type.

```rust
use azure_identity::DeveloperToolsCredential;
use azure_data_cosmos::{
    CosmosClient, AccountReference, AccountEndpoint, RoutingStrategy,
};

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    // Local dev: DeveloperToolsCredential. Production: use ManagedIdentityCredential.
    let credential = DeveloperToolsCredential::new(None)?;
    let endpoint: AccountEndpoint = "https://<account>.documents.azure.com/"
        .parse()?;
    let account = AccountReference::with_credential(endpoint, credential);
    let client = CosmosClient::builder()
        .build(account, RoutingStrategy::ProximityTo("East US".into()))
        .await?;
    Ok(())
}
```

Prefer the crate README/examples when checking builder signatures and CRUD method shapes instead of reconstructing APIs from memory or generated internals.

## Client Hierarchy

| Client            | Purpose                   | Access                                          |
| ----------------- | ------------------------- | ----------------------------------------------- |
| `CosmosClient`    | Account-level operations  | `CosmosClient::builder().build(account).await?` |
| `DatabaseClient`  | Database operations       | `client.database_client("db")`                  |
| `ContainerClient` | Container/item operations | `database.container_client("c").await`          |

## Core Workflow

```rust
use serde::{Serialize, Deserialize};
use azure_data_cosmos::CosmosClient;

#[derive(Serialize, Deserialize)]
struct Item {
    pub id: String,
    pub partition_key: String,
    pub value: String,
}

async fn crud(client: CosmosClient) -> Result<(), Box<dyn std::error::Error>> {
    let container = client
        .database_client("myDatabase")
        .container_client("myContainer")
        .await;

    let item = Item {
        id: "1".into(),
        partition_key: "pk1".into(),
        value: "hello".into(),
    };

    // Create
    container.create_item("pk1", "1", item, None).await?;

    // Read
    let resp = container.read_item("pk1", "1", None).await?;
    let mut item: Item = resp.into_model()?;

    // Update
    item.value = "updated".into();
    container.replace_item("pk1", "1", item, None).await?;

    // Delete
    container.delete_item("pk1", "1", None).await?;
    Ok(())
}
```

### Patch Item

```rust
use azure_data_cosmos::{PatchInstructions, PatchOperation};

let patch = PatchInstructions::from(vec![
    PatchOperation::set("/value", serde_json::json!("patched")),
]);
let patched: Item = container
    .patch_item("pk1", "1", patch, None)
    .await?
    .into_model()?;
println!("Patched value: {}", patched.value);
```

## Key Auth (Optional)

From microsoft/skills, MIT.

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