How can I return the previous DataVersion in observable_source_asset so that it is marked as unchanged

In the context of

observable_source_asset

, the purpose of the observation function is to return a

DataVersion

that represents the current state of the source data. If the data has not changed, the observation function should return the same

DataVersion

as it did previously. This would indicate to Dagster that the data version has not changed, and therefore the source asset is unchanged. The documentation does not provide a direct example of returning the previous

DataVersion

in an

observable_source_asset

. However, it does describe how to define an observation function that computes and returns a

DataVersion

based on the content of a file, for example, by hashing the file contents. If the file content has not changed, the hash (and thus the

DataVersion

) would remain the same. Here is a conceptual approach based on the documentation's description of how

observable_source_asset

works: 1. Define an

observable_source_asset

with an observation function. 2. In the observation function, compute the

DataVersion

based on the current state of the source data. 3. If the source data has not changed since the last observation, the computed

DataVersion

should be identical to the previous one. 4. Return the computed

DataVersion

from the observation function. If you have access to the previous

DataVersion

(e.g., stored externally or retrievable through some mechanism), you could compare the newly computed

DataVersion

with the previous one. If they match, you return the previous

DataVersion

, indicating that the data has not changed. However, the documentation does not provide explicit code examples or mechanisms for retrieving and returning the previous

DataVersion

. If you need to implement such functionality, you may need to devise a custom solution that fits your specific use case and data source.