Building a "IN" query in Dynamo DB with aws-sdk-go

Question

I've come to learn that Dynamo DB has severe limitations in being able to provide other DB types (SQL, mongo, cassandara, ...) capabilities. Among them is something like in Mongo {attribute: {"$in": [...]}} or in SQL SELECT ... FROM ... WHERE column IN (...). I see that there is a "IN" operator but I am struggling to make a very efficient filter expression of searching to see if a attribute value is present in a given list. For example, if I have data like:

ID,Attr1,Attr2
1,abc,hi
2,def,hello
3,ghi,howdy

If I have a list to scan the table to find items with Attr2 as any of ["hallo", "hi", "hola", "howdy", "bounjour"] (with my query it should return item 1 and 3). This list size might not always be this; sometimes there maybe more elements or fewer elements. I ended up using something like:

filter := expression.Equal(expression.Name("Attr2"), expression.value(myList[0]))
for _, val := range myList[1:] {
  filter = filter.Or(expression.Equal(expression.Name("Attr2"), expression.Value(val)))
}

This seems to work but I worry the expression becoming too long and when I print out the expression it looks odd (the OR statements are nested).

{map[filter:((((#0 = :0) OR (#0 = :1)) OR (#0 = :2)) OR (#0 = :3)) OR (#0 = :4) projection:#1, #2, #3, #4, #5, #0, #6] map[#0:0xc0004b06e0 #1:0xc0004b06f0 #2:0xc0004b0700 #3:0xc0004b0710 #4:0xc0004b0720 #5:0xc0004b0730 #6:0xc0004b0740] map[:0:0xc000142500 :1:0xc0001425a0 :2:0xc000142640 :3:0xc0001426e0 :4:0xc000142780]}

I am trying to make it with "IN" condition operator but I can't get it work with a unknown size list. Any advice on making it work with a "IN" operator with a dynamic list to check against? I feel like my Go code might be changed on making it better. I'm bit of a novice in go, any advice? In mongo it was pretty simple to be able to check against a large list. Same with SQL. There doesn't seem to be a proper way in dynamodb as of now (May 2020).

Answer 1

Figured out a way to use the "IN" operator:

wordsToCheck := []string{"hallo", "hi", "hola", "howdy", "bounjour"}
y := []*dynamodb.AttributeValue{}
for _, val := range wordsToCheck {
    y = append(y, &dynamodb.AttributeValue{S: aws.String(val)})
}
scanInput := &dynamodb.ScanInput{
    TableName: aws.String("mytable"),
    ScanFilter: map[string]*dynamodb.Condition{
        "Attr2": {
            ComparisonOperator: aws.String("IN"),
            AttributeValueList: y,
        },
    },
}
data, err := dynamoclient.Scan(scanInput)

Hope this helps someone! It hasn't been easy to read through the AWS documentation.