php – 使用嵌套映射更新DynamoDB项的正确示例

2019年8月5日 225次阅读

我必须在这里遗漏一些简单的东西.此测试的目标是在现有Map中设置新元素.以下
PHP测试函数可以正常更新项目,但不是将person属性(Map)中间初始值设置为“T”,而是创建一个名为“person.mi”的新顶级属性并将其设置为“T” ”.

docs for Document Paths指定用于访问Map元素的点符号,所以….我不知道我缺少什么.

public function Z() {

    $ddb = DynamoDbClient::factory(array('region' => 'us-east-1')); // EC2 role security

    try {
        $response = $ddb->updateItem(array(
            "TableName" => "test",
            "Key" => array("id" => array("N" => 1)),
            "UpdateExpression" => "SET #fieldName = :value",
            "ExpressionAttributeNames" => array("#fieldName" => "person.mi"),
            "ExpressionAttributeValues" => array(":value" => array("S" => "T"))
        ));
    } catch (Exception $e) {
        throw new DDBException("Call to TestDDB->Z failed: " . $e->getMessage());
    }
}

谁知道我哪里错了？谢谢.

最佳答案 这是因为点被认为是属性名称的一部分.您应该使用2个表达式属性名称.从
documentation：

But what if you decided to use an expression attribute name instead?
For example, what would happen if you were to define #mmmk as a
substitute for MyMap.MyKey? DynamoDB would return an empty result,
instead of the expected string. This is because DynamoDB interprets a
dot in an expression attribute value as a character within an
attribute’s name. When DynamoDB evaluates the expression attribute
name #mmmk, it determines that MyMap.MyKey refers to a scalar
attribute—which is not what was intended.

The correct approach would be to define two expression attribute
names, one for each element in the document path:

  • #mm — MyMap

  • #mk — MyKey

You could then use the following projection expression:

  • #mm.#mk
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