使用amplify-cli生成的变更(mutation)时，增强的订阅过滤连接错误。

Question

【以下的问题经过翻译处理】 我正在使用amplify-cli和angular前端。

我有以下模式（schema.graphql）：

`` `
type CardDeck @model
@key(name: "byBoard", fields: ["boardId"], queryField: "cardDeckByBoardId")
{
  id: ID!
  type: String!
  properties: [PropertyOrderTwo]
  boardId: ID!
}

type Subscription {
   onUpdateCardDeckByBoardId(boardId: ID!): CardDeck @aws_subscribe(mutations: "updateCardDeck")
}

`` `

我在 appSync 控制台中为订阅添加了以下响应映射模板。

`` `
## Response Mapping Template - onUpdateCardDeckByBoardId subscription

$extensions.setSubscriptionFilter({
    "filterGroup": [
        {
           "filters" : [
                {
                    "fieldName" : "boardId",
                    "operator" : "eq",
                    "value" : "**** -> a valid board id"
                }
           ]
           
        }
    ]
})

$util.toJson($context.result)

`` `

当我在应用程序中订阅侦听器时，会出现以下连接错误：

`` `
Connection failed: {"errors":[{"message":"Cannot return null for non-nullable type: 'ID' within parent 'CardDeck' (/onUpdateCardDeckByBoardId/id)"},{"message":"Cannot return null for non-nullable type: 'String' within parent 'CardDeck' (/onUpdateCardDeckByBoardId/type)"},{"message":"Cannot return null for non-nullable type: 'ID' within parent 'CardDeck' (/onUpdateCardDeckByBoardId/boardId)"},{"message":"Cannot return null for non-nullable type: 'AWSDateTime' within parent 'CardDeck' (/onUpdateCardDeckByBoardId/createdAt)"},{"message":"Cannot return null for non-nullable type: 'AWSDateTime' within parent 'CardDeck' (/onUpdateCardDeckByBoardId/updatedAt)"}]}

```
哪里出问题了呢？

Answer

【以下的回答经过翻译处理】 我按照AWS提供的教程进行了操作：

* 
*

显然，问题出在没有描述对象形状的数据源（NoneDS）的订阅会返回错误，因为它无法确保始终返回必填字段（id、type 和 boardId）。

实际上，直接从文档中，它们说：

> 
> $context.result: The value returned by the resolver from the data source. The shape of this object depends on the data source and operation.
>

为了解决此问题，可以使订阅的*response mapping template*返回一个默认负载，强制字段为空（或使用默认值填充）。

通过这种方式，我确实成功实现了订阅。

```
## Response Mapping Template - onUpdateCardDeckByBoardId subscription

$extensions.setSubscriptionFilter({
    "filterGroup": [
        {
           "filters" : [
                {
                    "fieldName" : "boardId",
                    "operator" : "eq",
                    "value" : "**** -> a valid board id"
                }
           ]
           
        }
    ]
})

## Workaround: In case of subscription with custom response template you must provide a valid payload that respects any mandatory fields defined in the model (in this case CardDeck has id, type, boardId and AppSync's default createdAt and updatedAt as mandatory fields).
$util.toJson({"id": "", "type": "", "boardId": "", "createdAt":"1930-01-01T16:00:00-07:00", "updatedAt":"1930-01-01T16:00:00-07:00"} )

```

使用amplify-cli生成的变更(mutation)时，增强的订阅过滤连接错误。

Response Mapping Template - onUpdateCardDeckByBoardId subscription

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