CODEWITHSUNDEEP
amazon-web-servicesamazon-dynamodbaws-sdk-go
Aditya Kumar Gupta
Aditya Kumar Gupta

Reputation: 133

How to set `ConditionExpression` for `dynamodb.UpdateItemInput ` using dynamodbiface.expression

expr := expression.Name("field1").Equal(expression.Value("val1"))
condition, err := expression.NewBuilder().WithCondition(expr).Build()
if err != nil { return err }
updateExpr := expression.Set(expression.Name("field2"), expression.Value("field2"))
update, err := expression.NewBuilder().WithUpdate(updateExpr).Build()
updateItemInput := &dynamodb.UpdateItemInput {
            TableName           :       aws.String("foobar"),
            Key:                        partitionKey,
            ConditionExpression:        condition.Condition(),

            UpdateExpression:           update.Update(),
            ExpressionAttributeNames:   update.Names(),
            ExpressionAttributeValues:  update.Values(),
            ReturnValues:               aws.String("UPDATED_NEW"),
        }

Above is what updateItemInput looks like right now. What I am trying to achieive with this is :

if field1 == "value1" then 
   set field2 = "value2"

Needless to say, this fails since the ExpressionAttributeNames and ExpressionAttributeValues doesnot have the context of condition.

What I have seen online and on StackOverflow is that people mostly write ConditionExpression string on their own, which I would want to avoid as much as possible.

So is there any way I can use dynamodbiface.expression to avoid writing the ConditionExpression manually?

Upvotes: 0

Views: 842

Answers (1)

Mike Dalrymple
Mike Dalrymple

Reputation: 1111

You just need a single expression and then you use the appropriate methods based on which input values you're trying to populate:

ex, e := expression.NewBuilder().
    WithCondition(expression.Name("field1").Equal(expression.Value("val1"))).
    WithUpdate(expression.
        Set(
            expression.Name("field2"),
            expression.Value("value2")).
    Build()
if e != nil {
    return e
}
updateItemInput := &dynamodb.UpdateItemInput{
    TableName:                 aws.String("foobar"),
    Key:                       partitionKey,
    ConditionExpression:       ex.Condition(),
    ExpressionAttributeNames:  ex.Names(),
    ExpressionAttributeValues: ex.Values(),
    UpdateExpression:          ex.Update(),
    ReturnValues:              aws.String("UPDATED_NEW"),
}

This is a slightly modified version of something I have working in production. I can't confirm that ReturnValues works as I don't use that but the rest is pretty much copy/paste from working code.

Upvotes: 1

Related Questions