Many-To-Many Relationships not working across multiple repositories

[solnic]

The following code is capable of reproducing the issue:

http://pastie.org/private/rsdhjt2chy2a15ycqfei0a

In this case, two of the models exist in the :default repository, the other exists in :inventory. Various combinations of repository() {} blocks vs. inline :repository => repository() attributes on the associations, changing :child_key to :target_key, etc...all fail with various other exceptions.

If I've defined the associations incorrectly, I apologize. This looks like it should work, but I have had no luck in 0.10 or prior. If there's any other information I can provide, please let me know. Thanks!

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Created by Matt Savona - 2009-06-26 13:01:17 UTC

Original Lighthouse ticket: http://datamapper.lighthouseapp.com/projects/20609/tickets/925

[solnic]

Attached is a script demonstrating how I would set it up. There is still a problem there, but hopefully this will provide a better example of how to set up cross-repository relationships.

The remaining problem is mostly due to the Query not recognizing that some of the relationships are from different repos, so it constructs a 3 table join to pull back the results, rather than breaking it up when going from Vip -> Interface.

by Dan Kubb (dkubb)

[solnic]

To be able to perform cross-repository many to many queries we are going to need to have a mechanism that can split up Query objects and perform each at the separate repositories, and feed the results of one into the query for the next.

This will also provide m:m to adapters that do not support joins natively, like the YAML, In-Memory, and basically every non-RDBMS adapter.

It is not likely that this will make it in for the 0.10.0 release, since it will be a rather large undertaking, so I am pushing this out to the next milestone.

by Dan Kubb (dkubb)

[solnic]

[project:id#20609 not-tagged:"0.10.0" not-tagged:"0.10.1" milestone:id#51895 bulk edit command]

by Dan Kubb (dkubb)

[solnic]

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by Dan Kubb (dkubb)

[solnic]

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by Dan Kubb (dkubb)

[solnic]

[bulk edit]

by Dan Kubb (dkubb)

[solnic]

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by Dan Kubb (dkubb)

[solnic]

I can confirm that this behaviour will not be implemented before DM 1.0 is released. Marking this as on-hold.

The only real way to solve this problem would be to rewrite the Query and Adapter APIs from the ground up. The adapters would need to perform as much of the query as they could natively, and then the join would need to happen in memory. This is a non-trivial problem, but I think it is solvable within the next year or two.

I’ve started work on a side project to address this problem, but it likely won’t be going into DM 1.0, and will probably form the base for DM 2.0: http://github.com/dkubb/veritas/

by Dan Kubb (dkubb)