About Relations

Relation is a basic dataclass that holds the information about the relation between the operations of the AWS services.

It's basically a description of where to find a required parameter's value in another operation's output.

Balcony traverses each operation, and finds the required parameters. Then it tries to find the Relations among required parameters and other operations outputs.

It can't always find the right relations, so some customization might be needed for some operations.

Relation class

@dataclass
class Relation:
    service_name: str        # AWS service name
    resource_node_name: str  # ResourceNode name
    operation_name: str      # given ResourceNode's specific operation name
    required_shape_name: str # Required parameter name for other operations
    target_shape_name: str   # Dict Key name from operation's output
    target_shape_type: str   # Data type of the `target_shape_name`
    target_path: str         # JMESPath selector for extracting the parameter values

Example Relation & How to read it

Example Relation

{
  "service_name": "iam",
  "resource_node_name": "Policy",
  "operation_name": "ListPolicies",
  "required_shape_name": "PolicyArn",
  "target_shape_name": "Arn",
  "target_shape_type": "string",
  "target_path": "Policies[*].Arn"
}

We could read this example relation like this:

• iam service has a Policy resource node, which has a ListPolicies operation.
• Arn is the key name of the output dictionary of the ListPolicies operation which has a "string" type.
• When you call ListPolicies, you can JMESPath search the response with target_path to get the Arn value out of the output.
• required_shape_name: "PolicyArn" is the name of the required parameter that could be populated using output of ListPolicies.

So if any operation had a PolicyArn as a required parameter, we could use the ListPolicies operation to get the Arn value from the output dictionary.