Add global Sequelize hook to make count behavior consistent with find

[svenaas]

In ORM queries incorporating association joins, Sequelize's count sometimes reports a larger number than the number of rows that Sequelize returns by the same query. This causes inconsistencies between the actual number of returned results and the number of total results reported, a problem which specifically comes up with some of our reports.

This PR adds a global beforeCount hook that changes Sequelize's default behavior to make count consistent. It also introduces a test which fails in the absence of this hook.

In addition to the test case, the misbehavior can be seen in the admin interface at /reports/users:

Without the hook a current local development instance will show 14 rows of user data:

but an inconsistent "total results: 17":

With the hook the total is consistent:

Background

In working on #4313 it came to my attention that some of our PaginatedQueryPages were displaying inconsistent information. Specifically, the "total results: n" in PaginationBanner differed from the number of rows shown.

@sknep identified this number as coming from the Sequelize's count via the paginate function in api/utils/index.js, and found other people reporting related issues.

This led me to sequelize/sequelize#9481 and from there to sequelize/sequelize#10557 where various workarounds are discussed. I experimented with simply adding distinct: true, but that caused other things to fail. What did work for me was James M. Greene's beforeCount hook, which I opted to place in api/models/index.js.

Changes proposed in this pull request:

• Adds global Sequelize hook
• Adds unit test for this hook in test/api/unit/models/sequelize-hook.test.js — is there a better place for this to live?

security considerations

None. This change is a bug fix that makes a reported count consistent with the size of the result set it refers to.

[svenaas]

Sorry to dismiss your review, @drewbo — I'd forgotten to link directly to the comment where the hook workaround came from.