Match non-partitionKey fields (in nested json) in both tables and retrieve data in DynamoDB table - amazon-web-services

Question

I have 2 tables, with 1 matching data in which I want to utilize that as a matching field and retrieve some data.
First table is this:
{
"mainFieldName": {
"S": "someString"
},
"fieldA": {
"L": [
{
"M": {
"AccountId": {
"S": "12345"
},
"PrincipalId": {
"S": "randomIdString"
},
"PrincipalType": {
"S": "GROUP"
}
}
},
{
"M": {
"AccountId": {
"S": "12345"
},
"PrincipalId": {
"S": "secondRandomString"
},
"PrincipalType": {
"S": "GROUP"
}
}
}
]
},
"fieldC": {
"L": [
{
"M": {
"name": {
"S": "xxx"
},
"final_json": {
"S": "some json data"
}
}
}
]
}
}
Second table:
{
"userId": {
"S": "randomString"
},
"group": {
"L": [
{
"M": {
"GroupId": {
"S": "randomGroupId"
}
}
}
]
}
}
I want to find the matched field for first table's fieldA.PrincipalId and second table's group.GroupId, if match, returning data is first table's fieldC.final_json
My params i tried is this, it's executed successfully but no results returned. I have confirmed there should be some matched inputs.
response = table1.scan(
TableName=TABLE_1,
FilterExpression="#gid.#pid = :id",
ExpressionAttributeValues={
':id': {'S': groupId}
},
ExpressionAttributeNames={
'#gid': 'groupId',
'#pid': 'PrincipalId'
}
)
It always return empty results

Answer 1

I managed to find a resolution to this. To simplify, I changed to a flatter table structure by pre-processing the Json to appending to a list.
My first table becomes:
{
"id": {
"S": "randomString"
},
"fieldA": {
"S": "randomString"
},
"table_1_groupId": {
"L": [
{
"S": "randomGroupIdString"
}
]
},
"fieldB": {
"S": "asdfsafd"
},
"fieldC": {
"L": [
{
"M": {
"name": {
"S": "randomString"
},
"jsonData": {
"S": "randomJsonData"
},
"type": {
"S": "type_a"
}
}
}
]
}
}
Second table stays the same.
With that i am able to use DynamoDB query which is more efficient as well, with FilterExpressions
My query is:
response = table1.query(
TableName=TABLE_1,
KeyConditionExpression="id = :id",
FilterExpression="contains(groupId, :gid)",
ExpressionAttributeValues={
':id': defaultId,
':gid': groupId
},
)
My output returns list of all data (since I haven't added any filter to the output) once they have the field 'GroupId' in Table2 match with table_1_groupId in table 1