扫描DynamoDB表时未显示ProjectionExpression中指定列的结果

Question

我正在尝试扫描DynamoDB故事，以便只获取筛选过的项。myTable有3列：L timestamp（String,PK）,colors（String）,userId（String）

var docClient = new AWS.DynamoDB.DocumentClient();

var params = {
    "TableName": "myTable",
    "ProjectionExpression": "colors, userId",
    "ExpressionAttributeValues": {":val": userId},
    "FilterExpression": "userId = :val"

};

console.log("Scanning table.");
docClient.scan((params), function(err,data){

    if (err) console.log(err, err.stack); 
    else console.log(data); //success response
});

因此，我只从userId列获取值。完全忽略列“colors”。

我做错了什么？

Answer 1

在ExpressionAttributeNames中设置ProjectionExpression属性。请查看以下代码片段

var docClient = new AWS.DynamoDB.DocumentClient();

 var params = {
  ExpressionAttributeNames: {
   "#colors": "colors", 
   "#userId": "userId"
  }, 
  ExpressionAttributeValues: {
    ":val": userId
  }, 
  FilterExpression: "userId = :val", 
  ProjectionExpression: "#colors, #userId", 
  TableName: "myTable"
 };

console.log("Scanning table."); 

docClient.scan(params, function(err, data) {
    if (err) console.log(err, err.stack); 
    else console.log(data); //success response
});

注意#和:必须分别出现在ExpressionAttributeNames和ExpressionAttributeValues上。