[RAG] How to extract generated strings from `RetrievAugLMMarginOutput`
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How to extract generated strings from `RetrievAugLMMarginOutput`?

## Details
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When using `RagSequenceForGeneration` and `retriever` separately we can't use `model.generate` (refer #7829). And calling `model.__call__` directly return `RetrievAugLMMarginOutput`. I not able to to find way to extract `generated_ids` from it. 

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**A link to original question on the forum/Stack Overflow**:
@patrickvonplaten can you please help<|||||>Hey @lalitpagaria,

Using embedding, retrieval and generation separately for RagSequence is not yet available sadly.
You should take a look into the `generate()` function of `RagSequenceForGeneration` for more detail on how to run it separately yourself.<|||||>Thanks @patrickvonplaten . I think we (haystack) will wait for implementation in transformers and use only RagToken for now.
Please let me know should I keep this open in case you plan to add functionality in the future? or close this.

cc: @tholor <|||||>Closing