# `case`

## Description

Returns a value from the first clause whose condition evaluates to `true`.

Each clause is a `condition -> value` pair: when `condition` evaluates to `true`, `case` returns `value`. You can include any number of clauses, plus an optional `_ -> default` fallback. If no condition matches and no fallback is present, `case` returns `null`.

Note

`case` checks clauses top-to-bottom and returns the **first match**, so order matters.

## Syntax

```dataprime
case {
condition1 -> value1,
condition2 -> value2,
...
conditionN -> valueN,
_          -> default
}
```

## Arguments

| Name               | Type   | Required  | Description                                                                                                                                                                            |
| ------------------ | ------ | --------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| condition -> value | clause | **true**  | A clause where `condition` is a boolean expression and `value` is what `case` returns when this is the first condition to evaluate to `true`. Repeat for as many branches as you need. |
| \_ -> default      | clause | **false** | Optional fallback clause. `default` is returned when no `condition` matches.                                                                                                           |

## Example

**Use case: Map server IPs to owners by subnet**

Suppose you want to enrich logs with the owner of each server based on its IP address. This can help route incidents to the right team.

You can use the `ipInSubnet` function inside a `case` statement to determine ownership. If no subnet matches, a default owner is assigned.

### Example data

```json
{
  "server_ip": "10.0.0.1"
},
{
  "server_ip": "165.0.0.1"
},
{
  "server_ip": "333.4.5.6"
}
```

### Example query

```dataprime
create server_owner from
case {
  ipInSubnet(server_ip, '10.0.0.0/8')   -> 'Chris',
  ipInSubnet(server_ip, '165.0.0.0/8')  -> 'George',
  ipInSubnet(server_ip, '333.4.0.0/16') -> 'Maya',
  _                                     -> 'DevOps Team'
}
```

### Example output

```json
{
  "server_ip": "10.0.0.1",
  "server_owner": "Chris"
},
{
  "server_ip": "165.0.0.1",
  "server_owner": "George"
},
{
  "server_ip": "333.4.5.6",
  "server_owner": "Maya"
}
```