[20 Days of DynamoDB] Day 5 - Avoid overwrites when using DynamoDB UpdateItem API

Posted: 12/Jan/2024

The UpdateItem API creates a new item or modifies an existing item's attributes. If you want to avoid overwriting an existing attribute, make sure to use the SET operation with if_not_exists function.

Here is an example that sets the category of an item only if the item does not already have a category attribute:

resp,err:=client.UpdateItem(context.Background(),&dynamodb.UpdateItemInput{TableName:aws.String(tableName),Key:map[string]types.AttributeValue{"email":&types.AttributeValueMemberS{Value:email},},UpdateExpression:aws.String("SET category = if_not_exists(category, :category)"),ExpressionAttributeValues:map[string]types.AttributeValue{":category":&types.AttributeValueMemberS{Value:category,},},})

Note that if_not_exists function can only be used in the SET action of an update expression.

Recommended reading - DynamoDB documentation