Sample: Flow Connection Server URL JSON Transformer

This sample demonstrates how to read and write JSON to update server and serverUrl in the flow JSON file before publishing. JSON transformers for flows should use the JsonContentTransformerBase<IPublishableFlow> base class, which handles opening the flow file, parsing the JSON, and persisting the modified JSON back to the file.

JSON transformers require additional resource overhead to execute, so care should be taken when developing them.

• Due to encryption, JSON transformers require the file to be loaded into memory to modify. For large flow files, this can require significant memory.
• Implementing the NeedsJsonTransforming/needs_json_transforming method can reduce overhead by letting the transformer skip loading flow files that do not require changes.

JSON transformers are provided with "raw" JSON and no file format validation is performed by the SDK. Care should be taken when modifying flow files that the changes do not result in content that is valid JSON but invalid by the file format. File format errors can lead to migration errors during publishing, and can also cause errors that are only apparent after the migration is complete and reported success.

• Python
• C#

Transformer Class

To update flow connection server values in Python, you can use the following transformer class:

from tableau_migration import (
    IPublishableFlow,
    JsonContentTransformerBase
)


class FlowConnectionServerJsonTransformer(JsonContentTransformerBase[IPublishableFlow]):

    def needs_json_transforming(self, ctx: IPublishableFlow) -> bool:
        # Returning false prevents the transform method from running.
        # Implementing this method potentially allows flows to migrate
        # without loading the file into memory, improving migration speed.
        return len(ctx.connections) > 0

    def transform(self, ctx: IPublishableFlow, json_obj: dict) -> None:
        # Changes to the JSON are saved back to the flow file before publishing.
        for _, connection in json_obj.get("connections", {}).items():
            attrs = connection.get("connectionAttributes", {})
            if attrs.get("server") == "https://old-server":
                attrs["server"] = "https://new-server"

Registration

plan_builder.transformers.add(FlowConnectionServerJsonTransformer)

See hook registration for more details.