GraphQL AppSync DynamoDB only update one field in mutation - graphql

Question

So I am working on an app with AWS amplify. I am using a single table design and I am trying to run a mutation where I only update the profile field of the UserV0 in the single table design. I am trying to only update the profile(s3key) but when I run my mutations it deletes the rest of the contents of UserV0.
Graph QL Schema
type SingleTable #model {
pk: String! #primaryKey(sortKeyFields: ["sk"])
sk: String!
user: UserV0
post: PostV0
}
type UserV0 {
name: String
username: String
email: String
profile: String
}
type PostV0 {
...
}
query getUserInfo {
getSingleTable(pk: "TEST", sk: "TEST") {
user {
username
name
profile
email
}
}
}
mutation createTable {
createSingleTable(input: {pk: "TEST", sk: "TEST", user: {email: "email#email.com", name: "testname", profile: "testPath", username: "testusername"}}) {
updatedAt
}
}
mutation updateTable {
updateSingleTable(input: {pk: "TEST", sk: "TEST", user: {profile: "TESTING", username: "TESTING123"}}) {
createdAt
}
}
If I run the update mutation above, then the entire user is reset and when I check it in my DynamoDB field the name and email fields are all lost. How can I make it so that when I run the mutation, I only update the profile field and leave the other fields without deleting them. Thanks in advance.
Edit: I put in all of the queries and mutations that I am running in AppSync. I run createTable and then getUserInfo and it returns this as it should.
{
"data": {
"getSingleTable": {
"user": {
"username": "testusername",
"name": "testname",
"profile": "testPath",
"email": "email#email.com"
}
}
}
}
But after I run the updateTable and then getUserInfo it returns this.
{
"data": {
"getSingleTable": {
"user": {
"username": "TESTING123",
"name": null,
"profile": "TESTING",
"email": null
}
}
}
}
As you can see the name and email fields are reset, set to null and removed from the DynamoDB database. I am pretty sure it is because it sees the user object as a new input. But how do I get it just recognize that I only want to update certain fields in userV0 and not the entire thing.

Answer 1

Make sure your function updateSingleTable uses the UpdateItem operation:
"operation" : "UpdateItem"
If you're using PutItem which I assume you are, it performs and overwrite and thus removing existing data.
https://docs.aws.amazon.com/appsync/latest/devguide/resolver-mapping-template-reference-dynamodb.html
Under the hood I believe the DynamoDB client is DynamoDB Mapper. As a result, it will delete values if set to null. To avoid this, you must ensure you do not set values to null, instead omit any values not being used in the request.