在Dynamo DB中查询索引

Question

I need an example in Go on how to do a query on an index in dynamo db. For JavaScript I found this one: https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/SQLtoNoSQL.Indexes.QueryAndScan.html

I could not find one for Go. I tried this:

    // Here "user_id" is the key, and
    // "user_id_index" is the secondary index

    keyCondition := expression.Key("user_id").Equal(expression.Value(userId))
    expr, errExpression := expression.NewBuilder().WithKeyCondition(keyCondition).WithProjection(proj).Build()

    if errExpression != nil {
        log.Printf("error: creating dynamo expression ", errExpression)

        return listResponse, errExpression
    }
    params := &dynamodb.QueryInput{
        ExpressionAttributeValues: expr.Values(),
        ProjectionExpression:      expr.Projection(),
        TableName:                 aws.String(tableName),
        IndexName:                 aws.String("user_id_index"),
        KeyConditionExpression:    expr.KeyCondition(),

    }
    result, errResults := svc.Query(params)

I get the following error:

error: scanning dynamo table %!(EXTRA *awserr.requestError=ValidationException:
 Invalid KeyConditionExpression: An expression attribute name used in the document path is not defined;
 attribute name: #0

Any link to a good tutorial would be appreciated, or code example as an answer too.

Answer 1

I think you're missing expression attribute names. Try adding this to your query input:

ExpressionAttributeNames:  expr.Names(),