根据数组中的嵌套属性过滤表达式 - DynamoDB

Question

I have a DynamoDB table where I store this data;

JSON data

where "device" is the partition key and "datetime" the sort key. I'm able to query data based on PartitionKey and range of dates (sort key). But now, I would need to filter based on "endpoint" which is inside "data" which is an array. For example, I would like to retrieve the data only if endpoint 1 exist in data array, or for example if endpoint IN (1,3) exist. I 'm using following code;

 var dev = event.params.querystring.device; var from = event.params.querystring.from; var to = event.params.querystring.to; var ascord = event.params.querystring.ascord; var limit = event.params.querystring.limit; var qryParams = { TableName : "mytable", KeyConditionExpression: "#id = :dddd and #tm between :time1 and :time2", FilterExpression: "data.endpoint = :ep", ExpressionAttributeNames:{ "#id": "device", "#tm": "datetime" }, ExpressionAttributeValues: { ":dddd": dev, ":time1": from, ":time2": to, ":ep": 1 } }; docClient.query(qryParams, function(err, data){ if (err){ callback(err, null); }else { callback(null, data); } }) 

But it doesn't retrieve any record. I also tried to use placeholders (#data.#endpoint) but didn't work. What would be the right way to do it? Also, should I create an index in the table for the endpoints?

Thanks for your help. Regards; Gus

Answer 1

The attribute data is a list of objects. So, DynamoDB can't find the item if you don't provide the array index of the list attribute. You can use contains function, if you know the value of endpoint and value .

Option 1 - Using contains:-

var params = {
    TableName: table,
    KeyConditionExpression: "#id = :dddd and #tm between :time1 and :time2",
    FilterExpression: "contains (#data, :ep)",
    ExpressionAttributeNames: {
        "#id": "deviceid",
        "#tm": "datetime",
        "#data" : "data"
    },
    ExpressionAttributeValues: {
        ":dddd": "1",
        ":time1": "2017-08-22T00:44:11:424Z",
        ":time2": "2017-08-22T23:44:11:424Z",
        ":ep": {
            "endpoint": 1,
            "value": "23"
        }
    }
};

Option 2 - Using Index :-

var params = {
    TableName: table,
    KeyConditionExpression: "#id = :dddd and #tm between :time1 and :time2",
    FilterExpression: "#data"+"[0].endpoint = :ep",
    ExpressionAttributeNames: {
        "#id": "deviceid",
        "#tm": "datetime",
        "#data" : "data"
    },
    ExpressionAttributeValues: {
        ":dddd": "1",
        ":time1": "2017-08-22T00:44:11:424Z",
        ":time2": "2017-08-22T23:44:11:424Z",
        ":ep": 1
    }
};