How to update one attribute value using ConditionExpression without affecting other attributes - DynamoDB

Question

I need to update Attribute Values of table items of DynamoDB. repeats section should update only if usersIDs Array consist with the user ID of current user.

Then I created ConditionExpression and run it.

var metricsParams = {
                TableName: table,
                Key:{
                   "metricsID" : metricsID,
                },
                UpdateExpression: "SET fans.orgID = :orgIDNew, fans.orgName = :orgNameNew, fans.noOfGamesPlayed = fans.noOfGamesPlayed + :val, Moment.datePlayed = :dateNew, Moment.monthPlayed = :monthNew, Moment.week = :weekNew, Moment.usersIDs = list_append(Moment.usersIDs, :usersNew), Moment.repeats = list_append(Moment.repeats, :repeateUsers)",
                ConditionExpression: "contains(Moment.repeats, :repeateUsers)",
                ExpressionAttributeValues:{
                    ":orgIDNew": body.team.id,
                    ":orgNameNew": body.team.domain,
                    ":val": 1,
                    ":dateNew" : Moment().format('LL'),
                    ":monthNew" : Moment().format("MMMM"),
                    ":weekNew" : Moment().format('WW'),
                    ":usersNew" : [body.user.id],
                    ":repeateUsers": [body.user.id]
                },
    
                ReturnValues:"UPDATED_NEW"
    
            };
            console.log("Attempting a conditional update...");
            metricsDoc.update(metricsParams, function(err, data) {
            if (err) {
            console.error("Unable to update item. *from id update* Error JSON:", JSON.stringify(err, null, 2));
            } else {
            console.log("UpdateItem succeeded: FROM DYNAMODB METRICS**", JSON.stringify(data, null, 2));

But when I add this ConditionExpression other Attributes also affect because of this. So How Can I fix this. Do i need to create seperate UpdateExpression?

Answer 1

You are correct. If you have multiple conditions, you will need multple operations. An operation can have 0-1 conditions, which applies to the operation as a whole:

Docs: If the condition expression evaluates to true, the operation succeeds; otherwise, the operation fail

Here are two options, given your current structure:

1. Make two update operations, one unconditional and one conditional. (note that list_append(Moment.repeats, :repeateUsers) does not guard against adding duplicate entries)
2. Make a query to retrieve the current record and, after determining what needs to be written, make one unconditional update operation.