CODEWITHSUNDEEP
goamazon-dynamodbaws-sdk-go
randobuzzer17
randobuzzer17

Reputation: 2238

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

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).

Upvotes: 0

Views: 1177

Answers (1)

randobuzzer17
randobuzzer17

Reputation: 2238

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.

Upvotes: 3

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