Reputation: 3288
I would like to update an item under certain conditions and then I would like to know whether the item was updated when UpdateItem returns.
The documentation seems contradictory to me.
On this page: http://docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_UpdateItem.html in the "Conditional Update" example it says "All of the item's attributes, as they appear after the update, are returned in the response."
On this page: https://godoc.org/github.com/aws/aws-sdk-go/service/dynamodb#UpdateItemOutput it says that Attributes is "A map of attribute values as they appeared before the UpdateItem operation"
I don't really want either of these. What I want is a bool that says whether or not there was an update.
This is where my brain is at now:
out, err := db.DynamoDB.UpdateItem(&dynamodb.UpdateItemInput{
TableName: tableName,
Key: map[string]*dynamodb.AttributeValue{
"KeyName": {S: aws.String(keyname)},
},
ExpressionAttributeNames: map[string]*string{
"#lock": aws.String("Lock"),
},
ExpressionAttributeValues: map[string]*string{
":now": aws.String(compfmt(time.Now())),
":promise": aws.String(compfmt(time.Now().Add(30 * time.Second))),
},
ConditionExpression: aws.String("attribute_not_exist(#lock) OR :now > #lock"),
UpdateExpression: aws.String("SET #lock = :promise"),
})
Upvotes: 3
Views: 8378
Reputation: 4510
There are now constants to compare the errors rather than using the hardcoded string as in other answers:
result, err := svc.UpdateItem(input)
if err != nil {
if aerr, ok := err.(awserr.Error); ok {
switch aerr.Code() {
case dynamodb.ErrCodeConditionalCheckFailedException:
fmt.Println(dynamodb.ErrCodeConditionalCheckFailedException, aerr.Error())
default:
fmt.Println(aerr.Error())
}
}
}
Upvotes: 3
Reputation: 464
One way to do this is to check the Code
on the awserr
import "github.com/aws/aws-sdk-go/aws/awserr"
func Lock()(bool, error) {
//Create value v
_, err := db.DynamoDB.UpdateItem(v)
if err != nil {
if ae, ok := err.(awserr.RequestFailure); ok && ae.Code() == "ConditionalCheckFailedException" {
return false, nil
}
return false, err
}
return true, nil
}
Upvotes: 5
Reputation: 3288
Turns out what I wanted to do was check the error to see if it contained the string ConditionalCheckFailedException
.
func Lock() (bool, error) {
...
_, err := db.DynamoDB.UpdateItem(v)
if err != nil {
if strings.Contains(err.Error(), "ConditionalCheckFailedException") {
return false, nil
}
return false, err
}
return true, nil
}
Upvotes: 1