[20 Days of DynamoDB] Day 17 - BatchGetItem operation

#dynamodb #serverless #database #cloud

Posted: 5/Feb/2024

You can club multiple (up to 100) GetItem requests in a single BatchGetItem operation - this can be done across multiple tables.

Here is an example that fetches includes four GetItem calls across two different tables:

    resp, err := client.BatchGetItem(context.Background(), &dynamodb.BatchGetItemInput{
        RequestItems: map[string]types.KeysAndAttributes{
            "customer": types.KeysAndAttributes{
                Keys: []map[string]types.AttributeValue{
                    {
                        "email": &types.AttributeValueMemberS{Value: "c1@foo.com"},
                    },
                    {
                        "email": &types.AttributeValueMemberS{Value: "c2@foo.com"},
                    },
                },
            },
            "Thread": types.KeysAndAttributes{
                Keys: []map[string]types.AttributeValue{
                    {
                        "ForumName": &types.AttributeValueMemberS{Value: "Amazon DynamoDB"},
                        "Subject":   &types.AttributeValueMemberS{Value: "DynamoDB Thread 1"},
                    },
                    {
                        "ForumName": &types.AttributeValueMemberS{Value: "Amazon S3"},
                        "Subject":   &types.AttributeValueMemberS{Value: "S3 Thread 1"},
                    },
                },
                ProjectionExpression: aws.String("Message"),
            },
        },
        ReturnConsumedCapacity: types.ReturnConsumedCapacityTotal,
    })

Just like an individual GetItem call, you can include Projection Expressions and return RCUs. Note that BatchGetItem can only retrieve up to 16 MB of data.

Recommended reading: BatchGetItem API doc