DynamoDB,how to query with BEGINS_WITH - amazon-dynamodb

Question

i'm using DocumentClient for query.
and using serverless framework with DynamoDb.
i'm trying to query with BEGINS_WITH without providing any primary key.
here is how my data looks like:
[
{
id: 1,
some_string: "77281829121"
},
{
id: 2,
some_string: "7712162hgvh"
},
{
id: 3,
some_string: "7212121"
}
]
here is my serverless.yml [i.e Table config i guess]:
Resources:
IPRecord:
Type: 'AWS::DynamoDB::Table'
Properties:
TableName: ${file(./serverless.js):Tables.IPRecord.name}
BillingMode: PAY_PER_REQUEST
AttributeDefinitions:
- AttributeName: 'id'
AttributeType: 'S'
- AttributeName: 'some_string'
AttributeType: 'S'
KeySchema:
- AttributeName: 'id'
KeyType: 'HASH'
GlobalSecondaryIndexes:
- IndexName: ${file(./serverless.js):Tables.IPRecord.index.ID}
KeySchema:
# ...some more index goes here
- AttributeName: 'some_string'
KeyType: 'RANGE'
Projection:
ProjectionType: 'ALL'
Q:
Using DocumentClinet i want to query with the first few elements of some_string.
which will return all the docs, that is matching.
like in this case i want to query {some_string:"77"} and it will return
[{
id: 1,
some_string: "77281829121"
},
{
id: 2,
some_string: "7712162hgvh"
}]
currently my query looks like this [this gives error ][Running in Local DynamoDB JS shell]:
var params = {
TableName: '<TABLE_NAME>',
IndexName: '<INDEX_NAME>',
KeyConditionExpression: 'begins_with(some_string,:value)',
ExpressionAttributeValues: {
':value': '77'
}
};
docClient.query(params, function(err, data) {
if (err) ppJson(err);
else ppJson(data);
});
seems like this above query needs a primary key, and in my case that is id. if i pass that, then it will point to a single doc.
Here is what i have achived so far:
var params = {
TableName: '<TABLE_NAME>',
FilterExpression: 'begins_with(some_string,:value)',
ExpressionAttributeValues: {
':value': '77'
},
Select:'COUNT' //as i only required COUNT
};
docClient.scan(params, function(err, data) {
if (err) ppJson(err);
else ppJson(data);
});
this above query does what i want.but
any better approach or solution always welcome.

Answer 1

if number of characters in your beginswith query is always going to be random, i don't see an option solving it with dynamodb.
but let's say there are going to be at least 3 characters. then you can do the following.
Update your dynamodb schema to
IPRecord:
Type: 'AWS::DynamoDB::Table'
Properties:
TableName: ${file(./serverless.js):Tables.IPRecord.name}
BillingMode: PAY_PER_REQUEST
AttributeDefinitions:
- AttributeName: 'id'
AttributeType: 'S'
- AttributeName: 'some_string'
AttributeType: 'S'
KeySchema:
- AttributeName: 'id'
KeyType: 'HASH'
- AttributeName: 'some_string'
KeyType: 'RANGE'
And instead of storing
[
{
id: 1,
some_string: "77281829121"
},
{
id: 2,
some_string: "7712162hgvh"
},
{
id: 3,
some_string: "7212121"
}
]
store as
[
{
id: 772,
uniqueid:1,
some_string: "77281829121"
},
{
id: 771,
uniqueid:2,
some_string: "7712162hgvh"
},
{
id: 721,
uniqueid:3,
some_string: "7212121"
}
]
Where id is always the first 3 character of original some_string.
Now let's say you have to query all items that start with abcx you can do
select * where id=abc and some_string startswith abcx
but you should always try to have more number of characters in id so that load is randomly distributed. for example if there are only 2 character only 36*36 ids are possible if there are 3 character 36*36*36 ids are possible.