= while
:type: processor
:status: stable
:categories: ["Composition"]



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component_type_dropdown::[]


A processor that checks a xref:guides:bloblang/about.adoc[Bloblang query] against each batch of messages and executes child processors on them for as long as the query resolves to true.


[tabs]
======
Common::
+
--

```yml
# Common config fields, showing default values
label: ""
while:
  at_least_once: false
  check: ""
  processors: [] # No default (required)
```

--
Advanced::
+
--

```yml
# All config fields, showing default values
label: ""
while:
  at_least_once: false
  max_loops: 0
  check: ""
  processors: [] # No default (required)
```

--
======

The field `at_least_once`, if true, ensures that the child processors are always executed at least one time (like a do .. while loop.)

The field `max_loops`, if greater than zero, caps the number of loops for a message batch to this value.

If following a loop execution the number of messages in a batch is reduced to zero the loop is exited regardless of the condition result. If following a loop execution there are more than 1 message batches the query is checked against the first batch only.

The conditions of this processor are applied across entire message batches. You can find out more about batching xref:configuration:batching.adoc[in this doc].

== Fields

=== `at_least_once`

Whether to always run the child processors at least one time.


*Type*: `bool`

*Default*: `false`

=== `max_loops`

An optional maximum number of loops to execute. Helps protect against accidentally creating infinite loops.


*Type*: `int`

*Default*: `0`

=== `check`

A xref:guides:bloblang/about.adoc[Bloblang query] that should return a boolean value indicating whether the while loop should execute again.


*Type*: `string`

*Default*: `""`

```yml
# Examples

check: errored()

check: this.urls.unprocessed.length() > 0
```

=== `processors`

A list of child processors to execute on each loop.


*Type*: `array`