AWS AppSync GraphQL query a record by a field value - amazon-dynamodb

Question

I have an user table, which consists of email, phone etc., and I would like to query a record based on its email or phone value (instead of #Id). Having not-adequate knowledge to do this - I wrote a schema like this:
type Query {
...
getUser(id: ID!): User
getUserByEmail(input: GetUserByEmailInput!): User
...
}
input GetUserByEmailInput {
email: String!
}
In resolver against getUserByEmail(..), I tried to experiment but nothing worked so far, so its remain to default state:
So when I ran a query like this to the Queries console:
query GetUserByEmail {
getUserByEmail(input: {email: "email#email.com"}) {
id
name
email
image
}
}
this returns an error like this:
{
"data": {
"getUserByEmail": null
},
"errors": [
{
"path": [
"getUserByEmail"
],
"data": null,
"errorType": "DynamoDB:AmazonDynamoDBException",
"errorInfo": null,
"locations": [
{
"line": 41,
"column": 5,
"sourceName": null
}
],
"message": "The provided key element does not match the schema (Service: AmazonDynamoDBv2; Status Code: 400; Error Code: ValidationException; Request ID: xxx)"
}
]
}
How can I query a record by non-Id field value?

Answer 1

If you use the Create Resources flow in the console, it will create a listUsers query that looks like the following for example. Note that the DynamoDb operation will be a Scan that has a DynamoDb filter expression where you can use any field to query DynamoDb. See below for the mapping template.
{
"version": "2017-02-28",
"operation": "Scan",
"filter": #if($context.args.filter) $util.transform.toDynamoDBFilterExpression($ctx.args.filter) #else null #end,
"limit": $util.defaultIfNull($ctx.args.limit, 20),
"nextToken": $util.toJson($util.defaultIfNullOrEmpty($ctx.args.nextToken, null)),
}
You can find more details about Scans and filter expressions in the AWS AppSync documentation:
https://docs.aws.amazon.com/appsync/latest/devguide/tutorial-dynamodb-resolvers.html