How to query AWS DynamoDb using KeyConditionExpression with the v2 Go SDK?

Question

I have an existing table in dynamodb created with the following command

aws dynamodb create-table \
  --region us-east-1 \
  --table-name notifications \
  --attribute-definitions AttributeName=CustomerId,AttributeType=S AttributeName=Timestamp,AttributeType=N AttributeName=MessageId,AttributeType=S \
  --key-schema AttributeName=CustomerId,KeyType=HASH AttributeName=Timestamp,KeyType=RANGE \
  --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5 \
  --global-secondary-indexes '[
      {
          "IndexName": "MessageId",
          "KeySchema": [
              {
                  "AttributeName": "MessageId",
                  "KeyType": "HASH"
              }
          ],
          "Projection": {
              "ProjectionType": "ALL"
          },
          "ProvisionedThroughput": {
              "ReadCapacityUnits": 5,
              "WriteCapacityUnits": 5
          }
      }
  ]'
}

And i want to put an API wrapper in front of it that allows me to get all records from the table provided a CustomerId, so I am attempting to use query from the v2 GO SDK

// GET /notifications/
func (api NotificationsApi) getNotifications(w http.ResponseWriter, r *http.Request) {
    var err error

    customerId := r.URL.Query().Get("customerId")
    if customerId == "" {
        api.errorResponse(w, "customerId query parameter required", http.StatusBadRequest)
        return
    }
    span, ctx := tracer.StartSpanFromContext(r.Context(), "notification.get")
    defer span.Finish(tracer.WithError(err))

    keyCond := expression.Key("CustomerId").Equal(expression.Value(":val"))
    expr, err := expression.NewBuilder().WithKeyCondition(keyCond).Build()

    input := &dynamodb.QueryInput{
        TableName:              aws.String("notifications"),
        KeyConditionExpression: expr.KeyCondition(),
        ExpressionAttributeValues: map[string]dynamodbTypes.AttributeValue{
            ":val": &dynamodbTypes.AttributeValueMemberS{Value: customerId},
        },
    }

    fmt.Println(*expr.KeyCondition())
    output, err := api.dynamoClient.Query(ctx, input)

    fmt.Println(output)
    fmt.Println(err)
}

However, I am getting a 400 from dynamodb

operation error DynamoDB: Query, https response error StatusCode: 400, RequestID: *****, api error ValidationException: Invalid KeyConditionExpression: An expression attribute name used in the document path is not defined; attribute name: #0

The output from fmt.PrintLn(*expr.KeyCondition()) is #0 = :0

Running this query locally returns my expected result

awslocal dynamodb query \
    --table-name notifications \
    --key-condition-expression "CustomerId = :val" \
    --expression-attribute-values '{":val":{"S":"localTesting"}}'

I have tried including the timestamp as well, but dont think that would be required since my terminal command without it works. I dont think im dereferencing improperly. I know my dynamo session is valid because i can POST to my wrapper and see updates via the terminal command.

Answer 1

Here's an example of a Query which you can use as a template:

// TableBasics encapsulates the Amazon DynamoDB service actions used in the examples.
// It contains a DynamoDB service client that is used to act on the specified table.
type TableBasics struct {
    DynamoDbClient *dynamodb.Client
    TableName      string
}



// Query gets all movies in the DynamoDB table that were released in the specified year.
// The function uses the `expression` package to build the key condition expression
// that is used in the query.
func (basics TableBasics) Query(releaseYear int) ([]Movie, error) {
    var err error
    var response *dynamodb.QueryOutput
    var movies []Movie
    keyEx := expression.Key("year").Equal(expression.Value(releaseYear))
    expr, err := expression.NewBuilder().WithKeyCondition(keyEx).Build()
    if err != nil {
        log.Printf("Couldn't build expression for query. Here's why: %v\n", err)
    } else {
        response, err = basics.DynamoDbClient.Query(context.TODO(), &dynamodb.QueryInput{
            TableName:                 aws.String(basics.TableName),
            ExpressionAttributeNames:  expr.Names(),
            ExpressionAttributeValues: expr.Values(),
            KeyConditionExpression:    expr.KeyCondition(),
        })
        if err != nil {
            log.Printf("Couldn't query for movies released in %v. Here's why: %v\n", releaseYear, err)
        } else {
            err = attributevalue.UnmarshalListOfMaps(response.Items, &movies)
            if err != nil {
                log.Printf("Couldn't unmarshal query response. Here's why: %v\n", err)
            }
        }
    }
    return movies, err
}

You can see more GoV2 examples here