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

The if step's settings in the pipeline editorThe if step's settings in the pipeline editor
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 does.

condition expression required

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

Examples
status >= 400status >= 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, 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 in a branch removes only records on that branch.

If step or step filter

Every step but If and 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

The if step's settings in the pipeline editorThe if step's settings in the pipeline editor
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