---
id: text--json-de-serializer
title: "Json deserializer"
summary: "Parses JSON text into objects of a flow type. The target type is not configured: it is the type of the connection on the `Output` pin. A JSON array produces one message per element; the elements can form a batch."
audience: user
keywords: "input, output, batchmode"
---
# Json deserializer

Parses JSON text into objects of a flow type. The target type is not configured: it is the type of the connection on the `Output` pin. A JSON array produces one message per element; the elements can form a batch.

## Pins

| Pin | Kind | Types | Description |
|---|---|---|---|
| Input | input | `Viaducta.Plugins.TextPlugin.Types.TextRecord`, `Viaducta.Plugins.Http.Types.WebHttpResponse`, `Viaducta.Plugins.Http.Types.WebHttpRequest`, `Viaducta.Plugins.UdpTypes.UdpDatagram`, `Viaducta.Plugins.Event.Types.EventData` | The JSON source: `TextRecord.Value`, `WebHttpResponse.Body`, `WebHttpRequest.Body` (or `ByteBody` as UTF-8 when `Body` is empty), `UdpDatagram.Data` (UTF-8) or `EventData.Data` (UTF-8). |
| Output | output | type of the output connection | One object of the connection's type per JSON object. |

## Configuration

| Field | Type | Default | Description |
|---|---|---|---|
| `BatchMode` | dropdown: `1` Auto, `2` Always, `3` Never | `1` | Whether the elements of a JSON array form a batch for batch consumers (Write file, Bulk insert, Build array). `Auto`: only if the input record is not already in a batch (Http client, events); inside a batch (e.g. a file read by Read file) the elements stay in that batch. `Always`: a child batch per array. `Never`: no batch. |

## Behaviour

- Target type: when the flow starts, the plugin takes the type set on the output connection (for example a type you created or imported from a JSON sample/schema). Choose the type on the connection; JSON property names are matched to the type's properties.
- JSON object (text not starting with `[`): deserialized into one object and emitted; no batch.
- JSON array: deserialized into a list of the target type; each element is emitted separately. When a batch is opened (`BatchMode`) it ends after the last element was processed downstream: batch consumers commit then, an error that reaches the deserializer fails the batch and they roll back. The batch label is `TextRecord.Name` when set. An empty array emits nothing and opens no batch.
- Record positions (`First`/`Last`) are not set.
- No output connection: nothing is done.
- Invalid JSON or JSON that doesn't fit the type raises an error handled by the flow's error handling.

## Notes

- Components that still collect by record position (Json serializer with batching, Csv encoder, ...) don't see array boundaries any more; they must use batches.
- An empty or missing body (e.g. `WebHttpResponse.Body` null, `EventData.Data` null) raises an error naming the input type.
- If the output pin has several connections with different types, the flow fails at start: all output connections must use the same type.
- The JSON root must match the target type: to read `{ "items": [ ... ] }` use a type with an `items` list property (or a script), not the element type.

## Example

No configuration. Placement:

Http client → **Json deserializer** (output connection type `Order`) → Data mapper → Database writer

Http listener → Webhook receiver → **Json deserializer** (output connection type `OrderCreated`) → ...