Feature Request: Add source for Firebase JSON

[mjrousos]

Google Firebase stores data as a JSON document but the JSON format is a little different from the JSON format used by the Data Transfer tool (Firebase stores all items as 'nodes' in a single JSON object, rather than as elements of an array; the nodes' keys are the IDs rather than having a field in the item serve as the ID).

It would be useful for migrating data from Firebase to Cosmos DB to have a Data Transfer source for Firebase-style JSON files.

[mjrousos]

Some things to consider when adding this support -

• Oftentimes, top level Firebase nodes are similar to CosmosDB collections, so it would be useful for the source to have an option to use items' top-level node as their collection in the target DB. I'm not sure if this would be feasible or not, though, since it seems like destination collection is always specified in the target instead of in the source or in individual data items. One option might be to add new fields to the items if this option is selected that the target could later look at to determine the correct collection for the item.
  • If this isn't possible, a good work-around would be to allow users of the Firebase source to optionally specify which node of a JSON document they want to import from and then they can just import one top-level node into a corresponding collection at a time.
• If this source would be sufficiently similar to existing JSON sources, we could just tweak them to accept this sort of input as an alternative schema. Based on my brief poking around in the tool's source, though, I suspect it would be cleaner to just have a separate Firebase source.

[mjrousos]

Fyi, I'm working on adding this support. Will open a PR soon.

[mjrousos]

cc: @conniey @JJVertical (should have added you to the PR, probably, instead of this issue, but it's linked #51 ).