Query multiple data with array of primary ids in DynamoDB

Question

I'm working on a application that is using DynamoDB as the database. I have a table of users like:

{
   id: 1, (Primary Key)
   name: "Indranil"
}

Now my requirement is, I have the array if ids like : [1,5,8] and I want to load all the users using single query.

Now I'm using the id as keyConditionExpreassion in the query and I can fetch each user data one after another, but then it'll result in multiple queries.

    let readparams  = {
      TableName : "user",
      KeyConditionExpression: "# = :",
      ExpressionAttributeNames:{
        "#": "id"
      },
      ExpressionAttributeValues: {
        ":id":1
      }
    };

Then I saw there is an 'IN' operation in the expressions but that can't be used in the KeyConditionExpression, it can be used in FilterExpreassion but in filterExpression I can't use primary key. And moreover I can't pass only filter expression in the query I have to pass a key expression as well but in my case I don't have any other condition to check.

    let readparams  = {
      TableName : "user",
      FilterExpression: "id IN (:id1, :id2)",
      ExpressionAttributeValues: {
        ":id1":1,
        ":id2":1
      }
    };

So eventually I've left with only option, to load all the data in the frontend and then filter those using ids in the frontend, but obviously that's not a good solution at all.

Can someone please point out what is the best solution here.

notionquest · Accepted Answer · 2017-11-16 12:08:37Z

11

Batch get item API can be used to get multiple items by key attributes. If you have sort key defined for your table, you need to provide both partition and sort key attribute value.

Batch get item

Some sample code:-

var table = "phone";

var params = {
    "RequestItems" : {
        "phone" : {
            "Keys" : [ {
                "phone_num" : "+14085551212",
                "Country" : "USA"
            },
            {
                "phone_num" : "+14085551313",
                "Country" : "USA"
            }
             ]
        }
    }

};

docClient.batchGet(params, function(err, data) {
    if (err) {
        console.error("Unable to read item. Error JSON:", JSON.stringify(err,
                null, 2));
    } else {
        console.log("GetItem succeeded:", JSON.stringify(data, null, 2));
    }
});

answered Nov 16, 2017 at 12:08

notionquest

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4 Comments

Vasiliy Ivanov Over a year ago

I have partition and sort key for table but I don't know the sort key for all partition ids. Should I use query?

Yang Over a year ago

note if you have more than 100 result batchGet will blow up see docs.aws.amazon.com/amazondynamodb/latest/APIReference/… ,

ffleandro Over a year ago

Also note that BatchGetItem can't be used against GSIs.

JHH Over a year ago

If your primary key is a single unique ID, what reason could there be to have a sort key in the first place? That makes no sense. The best thing would be if the users you're querying would share some other attribute which you could build an index on. For example, if you're always querying users from the same organization, you could have an index on organizationId. But all you do have is an array of random IDs with no common denominator, a batch get is your best bet.

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