---
id: flow--decision-plugin
title: "Decision router"
summary: "Routes each record to one of several branches. A C# script returns a route name for the record; the record is sent to the outgoing connections whose route id equals that name. Use it for if/else and switch-like branching."
audience: user
keywords: "input, output, condition"
---
# Decision router

Routes each record to one of several branches. A C# script returns a route name for the record; the record is sent to the outgoing connections whose route id equals that name. Use it for if/else and switch-like branching.

## Pins

| Pin | Kind | Types | Description |
|---|---|---|---|
| Input | input | any | Records to route. |
| Output | output | same as input | The unchanged input record. Draw one connection per branch from this pin and set the connection's route id (connection properties) to the route name. |

## Configuration

| Field | Type | Default | Description |
|---|---|---|---|
| `Condition` | string (C# code editor) | generated template | C# code containing the method `GetRoute` (see below). |

### The Condition script

The script is the body of a class; it must contain exactly this method:

```csharp
public string GetRoute(IMetaData metaDataInstance, IViaType inputDataInstance)
{
    var metaData = (MyFlowNamespace.FlowMetaData)metaDataInstance;
    var inputData = (MyFlowNamespace.Order)inputDataInstance;
    if (inputData.Amount > 1000) return "Large";
    return "Small";
}
```

- The returned string is the route name. It is compared exactly (case-sensitive) with the route id of each outgoing connection.
- The template generated by the designer casts the metadata to the flow's `FlowMetaData` and the input to the input connection's type; adjust the cast when the input type changes.
- `using` statements can be written anywhere in the script; they are moved to the top. Common namespaces (`System`, `System.Linq`, `System.Collections.Generic`, `Viaducta.TypeSystem`, `Viaducta.TypeSystem.Metadata`, `Viaducta.Plugin.Design`, the flow namespace, ...) are already imported. NuGet packages of the flow can be used.
- The property `Services` (`IFlowService`) is available in the script for logging, flow properties, etc.

## Behaviour

- For each record a new script instance is created, `GetRoute` is called and the result is stored as the record's route id; the record is then sent to `Output`.
- Delivery from `Output`:
  - connections with a route id receive the record only when the route id equals the returned name;
  - connections without a route id receive every record whose type matches (they are not an "else" branch).
- If no connection matches the returned name (for example the default template's empty string), the record is dropped silently.
- An exception thrown by the script fails the record (normal error handling of the flow applies).
- Without a script the designer shows a "no condition" indicator and a warning; the default template returns an empty string.

## Notes

- To build an "else" branch, return an explicit name for it (for example `"Other"`) and set that route id on the connection; do not leave a connection without a route id.
- The route id is stored on the record object itself. If a downstream component passes the same record on, the route id travels with it and can affect other route-id connections later in the flow.
- The script runs on every record; keep it fast and free of side effects.

## Example

Script returns `"Large"` or `"Small"`:

Http listener → **Decision router** → (route id `Large`) Approval flow ; (route id `Small`) Database writer