Pipeline reference

# If step

An If step reads a condition on each record and runs its **then** steps where the condition is true and its **else** steps everywhere else.

Each branch, **then** or **else**, is a step list of its own, which you edit inside the If step's card.

## Example

Step

  Saved JSON

```
{
  "id": "branch",
  "type": "if",
  "condition": "status >= 500",
  "then": [
    {
      "id": "severity-error",
      "type": "eval",
      "assignments": [{ "target": "severity", "expr": "\"error\"" }]
    },
    {
      "id": "page",
      "type": "eval",
      "assignments": [{ "target": "page", "expr": "true" }]
    }
  ],
  "else": [
    {
      "id": "severity-normal",
      "type": "eval",
      "assignments": [{ "target": "severity", "expr": "\"normal\"" }]
    },
    {
      "id": "drop-health",
      "type": "drop",
      "condition": "path == \"/health\""
    }
  ]
}
```

Input

```
{
  "status": 503,
  "path": "/pay"
}
```

```
{
  "status": 200,
  "path": "/home"
}
```

```
{
  "status": 200,
  "path": "/health"
}
```

→

Output

```
{
  "status": 503,
  "path": "/pay",
  "severity": "error",
  "page": true
}
```

```
{
  "status": 200,
  "path": "/home",
  "severity": "normal"
}
```

The parser declares `status` as `i64` and `path` as `str`. The 503 record takes the then branch; the two 200 records take the else branch, where the Drop step removes the `/health` record.

## Settings

It also takes an `id`, as [every step](/docs/steps#settings) does.

`condition`  expression required

A bool expression. A null condition reads false. Any other type is refused when you save.

Examples:

- `status >= 400`
- `status >= 500 || status == 429`

`then`  list of steps default none

The steps for records where the condition is true.

Example:

- `[{"id": "mark","type": "eval","assignments": [{"target": "failed","expr": "true"}]}]`

`else`  list of steps default none

The steps for every other record.

Example:

- `[{"id": "quiet","type": "drop","condition": "true"}]`

## How it works

A record runs the steps of one branch, then continues with the step after the If step. An empty branch leaves its records unchanged.

A branch can hold any step but [Unroll](/docs/steps/unroll), including another If step; an Unroll step in a branch is an error when you save. It changes how many records there are, and a record that takes the other branch has no item of the array. Unroll before the If step, then select the new records with the If step's condition or a Drop step. A [Drop step](/docs/steps/drop) in a branch removes only records on that branch.

### If step or step filter

Every step but If and [Comment](/docs/steps/comment) has a **filter**. A filter selects the records that one step processes; the other records pass that step unchanged. An If step selects records for a whole list of steps, and gives the other records a list of their own.

A step inside a branch can also have a filter. It then processes the records where both the branch's condition and its filter hold.

### Null and missing fields

A condition that is null is not true, so the record takes the else branch. A record without `status` does:

Step

  Saved JSON

```
{
  "id": "branch",
  "type": "if",
  "condition": "status >= 500",
  "then": [
    {
      "id": "severity-error",
      "type": "eval",
      "assignments": [{ "target": "severity", "expr": "\"error\"" }]
    }
  ],
  "else": [
    {
      "id": "severity-normal",
      "type": "eval",
      "assignments": [{ "target": "severity", "expr": "\"normal\"" }]
    }
  ]
}
```

Input

```
{
  "path": "/pay"
}
```

→

Output

```
{
  "path": "/pay",
  "severity": "normal"
}
```

## See also

-   [Pipeline steps](/docs/steps)
-   [Unroll step](/docs/steps/unroll)
-   [Drop step](/docs/steps/drop)
-   [Comment step](/docs/steps/comment)
-   [Expression reference](/docs/code-reference)