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_existsfunction can only be used in theSETaction of an update expression.
Recommended reading - DynamoDB documentation
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