DynamoDb.net: Adding multiple scan conditions

Question

I am using Dynamodb.net here. How can I add multiple scan conditions so that the data is filtered out based on those conditions. I am using the below code:

var creds = new BasicAWSCredentials(awsId, awsPassword);
var dynamoClient = new AmazonDynamoDBClient(creds, awsDynamoDbRegion);
var context = new DynamoDBContext(dynamoClient);
List<ScanCondition> conditions = new List<ScanCondition>();
//  conditions.Add(new ScanCondition("Id", ScanOperator.Equal, myId));
conditions.Add(new ScanCondition("name", ScanOperator.Equal, myName));
var response = await context.ScanAsync<Data>(conditions).GetRemainingAsync();
return response;

In my code above if I add 2 scan conditions, it does not works. But does work with one condition. Not sure if what I am doing wrong here.

Mike Dinescu · Accepted Answer · 2018-06-30 14:53:22Z

9

Your code looks OK, with one caveat: scan conditions are for non-key attributes.

I'm going to go out on a limb and assume that Id is the partition key (or perhaps sort key) of your table. If that's true then that's why you can't use it in a scan condition. You can have multiple Scan conditions added but they must all be for non-key attributes.

In order to specify key conditions, you must use a Query operation, not a Scan.

Assuming your table only has a Primary key and no Sort key, then the example below should work. However, if the table has a sort key as well then your query must include that as well so the example below would need to be modified slightly.

var creds = new BasicAWSCredentials(awsId, awsPassword);
var dynamoClient = new AmazonDynamoDBClient(creds, awsDynamoDbRegion);
var context = new DynamoDBContext(dynamoClient);


var opConfig = new DynamoDBOperationConfig();
opConfig.QueryFilter = new List<ScanCondition>();
opConfig.QueryFilter.Add(new ScanCondition("name", ScanOperator.Equal, myName));
var response = await context.QueryAsync<Data>(myId, opConfig).GetRemainingAsync();
return response;

answered Jun 30, 2018 at 14:53

Mike Dinescu

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5 Comments

aman Over a year ago

Thanks Mike I believe yes I have to use Query and not scan. One more question though. Do you know how can we incorporate OR condition together with the And conditions. Say I have 3 AND conditions and one OR condition. The scenario I have is that I am using 3 AND conditions which are my page filters and the OR condition which is my page search. I have one API which I am calling for this. Because of very less information on dynamodb .net what I cam currently doing is using SCAN for AND conditions then using c# Linq for OR. Any how I could club AND and OR together? Thanks

Mike Dinescu Over a year ago

It is possible to include boolean logic in filter expressions using the low level client. See: docs.aws.amazon.com/amazondynamodb/latest/developerguide/…

Mike Dinescu Over a year ago

It looks like the Async client has limited support for boolean logic in conditional statements: docs.aws.amazon.com/sdkfornet/v3/apidocs/…

aman Over a year ago

Yes Mike I think for now i would continue to use filter with OR in my Linq. Thanks for your help.

user3042674 Over a year ago

You have probably moved on since this was written ;) I think the query language for dynamoDB is a bit limited compared to other databases like mongoDB, neo4J or relational databases (SQL).

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