生成 DynamoDBEvent 属性值的 JSON

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我正在编写一个 lambda，它从 dynamodb 表接收流数据。解析出正确的记录后，我尝试将其转换为 json。目前，我正在这样做：

func lambdahandler(ctx context.context, request events.dynamodbevent) error {

    // ...

    // not actual code, just for demonstration
    record = request.records[0]

    data, err := events.newmapattribute(record.change.newimage).marshaljson()
    if err != nil {
        return err
    }

    // ...
}

问题是这会产生如下所示的 json 负载：

{
  "m": {
    "action": { "n": "0" },
    "expiration": { "n":"0" },
    "id": { "s": "trades|v4|2023-02-08" },
    "order": { "n":"22947407" },
    "price": { "n":"96.139" },
    "sort_key": { "s":"22947407" },
    "stop_limit": { "n":"0" },
    "stop_loss": { "n":"96.7" },
    "symbol": { "s":"cadjpy" },
    "take_profit": { "n":"94.83" },
    "type": { "n":"5" },
    "type_filling": { "n":"0" },
    "type_time": { "n":"0" },
    "volume": { "n":"1" }
  }
}

如您所见，这模仿了 dynamodb 属性值的结构，但这不是我想要的。相反，我尝试生成如下所示的 json 有效负载：

{
  "action": 0,
  "expiration": 0,
  "id": "trades|v4|2023-02-08",
  "order": 22947407, 
  "price": 96.139,
  "sort_key": "22947407",
  "stop_limit": 0,
  "stop_loss": 96.7,
  "symbol": "CADJPY",
  "take_profit": 94.83,
  "type": 5,
  "type_filling": 0,
  "type_time": 0,
  "volume": 1
}

正确答案

我最终编写了一个函数，它或多或少地完成了我需要的功能。这会将数值写入字符串，但否则会生成我正在寻找的 json 有效负载：

// AttributesToJSON attempts to convert a mapping of DynamoDB attribute values to a properly-formatted JSON string
func AttributesToJSON(attrs map[string]events.DynamoDBAttributeValue) ([]byte, error) {

    // Attempt to map the DynamoDB attribute value mapping to a map[string]interface{}
    // If this fails then return an error
    keys := make([]string, 0)
    mapping, err := toJSONInner(attrs, keys...)
    if err != nil {
        return nil, err
    }

    // Attempt to convert this mapping to JSON and return the result
    return json.Marshal(mapping)
}

// Helper function that converts a struct to JSON field-mapping
func toJSONInner(attrs map[string]events.DynamoDBAttributeValue, keys ...string) (map[string]interface{}, error) {
    jsonStr := make(map[string]interface{})
    for key, attr := range attrs {

        // Attempt to convert the field to a JSON mapping; if this fails then return an error
        casted, err := toJSONField(attr, append(keys, key)...)
        if err != nil {
            return nil, err
        }

        // Set the field to its associated key in our mapping
        jsonStr[key] = casted
    }

    return jsonStr, nil
}

// Helper function that converts a specific DynamoDB attribute value to its JSON value equivalent
func toJSONField(attr events.DynamoDBAttributeValue, keys ...string) (interface{}, error) {
    attrType := attr.DataType()
    switch attrType {
    case events.DataTypeBinary:
        return attr.Binary(), nil
    case events.DataTypeBinarySet:
        return attr.BinarySet(), nil
    case events.DataTypeBoolean:
        return attr.Boolean(), nil
    case events.DataTypeList:

        // Get the list of items from the attribute value
        list := attr.List()

        // Attempt to convert each item in the list to a JSON mapping
        data := make([]interface{}, len(list))
        for i, item := range list {

            // Attempt to map the field to a JSON mapping; if this fails then return an error
            casted, err := toJSONField(item, keys...)
            if err != nil {
                return nil, err
            }

            // Set the value at this index to the mapping we generated
            data[i] = casted
        }

        // Return the list we created
        return data, nil
    case events.DataTypeMap:
        return toJSONInner(attr.Map(), keys...)
    case events.DataTypeNull:
        return nil, nil
    case events.DataTypeNumber:
        return attr.Number(), nil
    case events.DataTypeNumberSet:
        return attr.NumberSet(), nil
    case events.DataTypeString:
        return attr.String(), nil
    case events.DataTypeStringSet:
        return attr.StringSet(), nil
    default:
        return nil, fmt.Errorf("Attribute at %s had unknown attribute type of %d",
            strings.Join(keys, "."), attrType)
    }
}

此代码的工作原理是迭代顶级映射中的每个键和值，并将值转换为 interface{}，然后将结果转换为 json。在这种情况下，interface{} 可以是 []byte、[][]byte、string、[]string、bool、interface{} 或 phpcnc phpcnmap[string]interface{} 取决于类型属性值。

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