> ## Documentation Index
> Fetch the complete documentation index at: https://wundergraphinc-dominik-eng-8583-add-documentation-and-infor.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# General Usage

> General usage of Cosmo Streams Custom Modules across all available hooks

This page describes concepts that are shared across all Cosmo Streams handlers and apply to every available hook.

## Operation Variables

If your operation defines variables, you can access them through the `Variables` method on the `OperationContext` interface.

```go theme={null}
variables := ctx.Operation().Variables()
```

```graphql theme={null}
subscription($customerId: Int!) {
  orderUpdates(customerId: $customerId) {
    id
  }
}
```

Example variables payload:

```json theme={null}
{
  "customerId": 123
}
```

Inside your handler, you can retrieve the variables using the `Variables` method:

```go theme={null}
variables := ctx.Operation().Variables()
customerId := variables.Get("customerId").GetInt() // = 123
```

## Operation Arguments

If no variables are defined in the operation, or if you do not control the variables,
you can access arguments directly via the `OperationContext` interface.

```go theme={null}
arguments := ctx.Operation().Arguments()
```

Consider an operation that defines multiple arguments:

```graphql theme={null}
subscription {
  orderUpdates(customerId: "123", status: PENDING) {
    id
    items(first: 5, sortBy: "price") { name }
  }
}
```

To access the `customerId` argument of the subscription field, use the `Get` method:

```go theme={null}
customerId := ctx.Operation().Arguments().Get("orderUpdates", "customerId").GetStringBytes()
```

Because `orderUpdates` is the root field, you can also resolve the field name dynamically:

```go theme={null}
// For OnPublishEvent handler
rootFieldName := ctx.PublishEventConfiguration().RootFieldName()

// For OnReceiveEvent and SubscriptionOnStart handler
rootFieldName := ctx.SubscriptionEventConfiguration().RootFieldName()

customerId := ctx.Operation().Arguments().Get(rootFieldName, "customerId").Value()
```

To access arguments on nested fields, such as the `sortBy` argument of the `items` field,
use dot notation to reference the nested path.

```go theme={null}
sortBy := ctx.Operation().Arguments().Get("orderUpdates.items", "sortBy").GetStringBytes()
```

When a field uses an alias, the alias must be used as the key when accessing its arguments.

```graphql theme={null}
subscription {
  orderUpdates(customerId: "123", status: PENDING) {
    id
    cheapestItems: items(first: 3, sortBy: "price") { name }
    newestItems: items(first: 3, sortBy: "createdAt") { name }
  }
}
```

```go theme={null}
cheapestItemsSortBy := ctx.Operation().Arguments().Get("orderUpdates.cheapestItems", "sortBy").GetStringBytes()
newestItemsSortBy := ctx.Operation().Arguments().Get("orderUpdates.newestItems", "sortBy").GetStringBytes()
```

You can also work with more complex argument types, such as arrays and input objects.

```graphql theme={null}
subscription {
  orderUpdates(statuses: ["pending", "shipped"], filter: { minTotal: 100, currency: "USD" }) {
    id
  }
}
```

```go theme={null}
arguments := ctx.Operation().Arguments()

statuses := arguments.Get("orderUpdates", "statuses").GetArray()
filter := arguments.Get("orderUpdates", "filter").GetObject()
minTotal := filter.Get("minTotal").GetInt()
currency := filter.Get("currency").GetStringBytes()
```