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I have a SQLAlchemy-based tool for selectively copying data between two different databases for testing purposes. I use the merge() function to take model objects from one session and store them in another session. I'd like to be able to store the source objects in some intermediate form and then merge() them at some later point in time.

It seems like there are a few options to accomplish this:

  • Exporting DELETE/INSERT SQL statements. Seems pretty straightforward, I think I can get SQLAlchemy to give me the INSERT statements, and maybe even the DELETEs.
  • Exproting the data to a SQLite database file with the same (or similar) schema, that could then be read in as a source at a later point in time.
  • Serializing the data in some manner and then reading them back into memory for the merge. I don't know if SQLAlchemy has something like this built-in or not. I'm not sure what the challenges would be in rolling this myself.

Has anyone tackled this problem before? If so, what was your solution?

EDIT: I found a tool built on top of SQLAlchemy called dataset that provides the freeze functionality I'm looking for, but there seems to be no corresponding thaw functionality for restoring the data.

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I haven't used it before, but the dogpile caching techniques described in the documentation might be what you want. This allows you to query to and from a cache using the SQLAlchemy API:

http://docs.sqlalchemy.org/en/rel_0_9/orm/examples.html#module-examples.dogpile_caching

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I think this will work, although I still have not had time to implement it yet. Thanks!

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