Node.js 使用Lambda将项添加到DynamoDB中映射嵌套的数组中

我试图将一个项目添加到一个列表中，该列表嵌套在DynamoDB中的另一个对象列表中。我正在传递

“userid”：“041c9004”

和

“author”：“J.K Rowling”

。我想将字符串“hermoine”添加到

图书

列表第二项中的

字符

列表中。函数首先在图书列表中查找“J.K Rowling”对象的索引。然后，它应该使用该索引将字符串插入到正确的字符列表中。但是，此代码引发了一个错误

DynamoDB表看起来像这样。userid是主键：

{
  "books": [
    {
      "author": "J.R.R. Tolkien",
      "characters": ["frodo","sam","bilbo"],
      "title": "Lord of the Rings"
    },
    {
      "author": "J.K Rowling",
      "characters": ["harry","ron"],
      "title": "Harry Potter"
    }
  ],
  "lastupdated": 1597690265,
  "userid": "041c9004"
}

以下是Lambda函数：

const AWS = require('aws-sdk');
const docClient = new AWS.DynamoDB.DocumentClient({region: 'us-east-1'});

exports.handler = function(event, context, callback){

    var params = {
        TableName: 'Users',
        Key: {
            userid: event.userid
        }
    };

    docClient.get(params, function(err, data){
        if(err) {
            callback(err,null);
        } else {
            var indexOfAuthor = data.Item.books.findIndex(i => i.author === event.author);
            console.log('The index of the author is ' + indexOfAuthor);
            
            if (indexOfAuthor == -1) {
                callback(err, null);
            } else {
                let paramsadd =  {
                    ExpressionAttributeValues: {
                        ":character": ["hermoine"]
                    },  
                    ExpressionAttributeNames : {
                        // this is likely where the issue is
                        "#attrName" : "books[" + indexOfAuthor + "].characters"
                    },
                    Key: {
                        userid: event.userid
                    },
                    TableName: 'Users',
                    UpdateExpression: "SET #attrName = list_append(#attrName, :character)",
                    ReturnValues:"ALL_NEW",
                };
        
                docClient.update(paramsadd, function(err,data){
                    if(err) {
                        callback(err, null);
                    }else{
                        callback(null, data);
                    }
                });
            }
        }
    });
};

这是引发的错误：

ERROR   Invoke Error    {"errorType":"ValidationException","errorMessage":"The provided expression refers to an attribute that does not exist in the item","code":"ValidationException","message":"The provided expression refers to an attribute that does not exist in the item"

以下是解决方案：

    docClient.get(params, function(err, data){
        if(err) {
            callback(err,null);
        } else {
            var indexOfAuthor = data.Item.books.findIndex(i => i.author === event.author).toString();
            console.log('The index of the author is ' + indexOfAuthor);
            var attrnamval = `books[${indexOfAuthor}].characters` ;
            
            if (indexOfAuthor == -1) {
                callback(err, null);
            } else {
                let paramsadd =  {
                    ExpressionAttributeValues: {
                        ":character": ["hermoine"]
                    },  
                    Key: {
                        userid: event.userid
                    },
                    TableName: 'Users',
                    UpdateExpression: `SET ${attrnamval} = list_append(${attrnamval}, :character)`,
                    ReturnValues:"ALL_NEW",
                };
        
                docClient.update(paramsadd, function(err,data){
                    if(err) {
                        callback(err, null);
                    }else{
                        callback(null, data);
                    }
                });
            }
        }
    });