Rollback on constraint failure

[joshbuddy]

This fixes an issue where deferred constraints can leave the transaction in an inconsistent state. In the event of a failed deferred constraint, we need to issue a rollback in order to make a transaction startable later.

[mattn]

@rittneje Do you have an opinion?

[rittneje]

Given that database/sql will not allow a transaction to be reused once you call Commit() (even if it fails), should we just issue a ROLLBACK on error, regardless of which specific error it was? The SQLite docs say this:

If the transaction has already been rolled back automatically by the error response, then the ROLLBACK command will fail with an error, but no harm is caused by this.

[joshbuddy]

Sounds good to me @rittneje. I've updated the PR and also updated the comment.

[rittneje]

Suggested change

	// to sqlite's docs, there is no hard in calling ROLLBACK unnecessarily.
	// to sqlite's docs, there is no harm in calling ROLLBACK unnecessarily.

[rittneje]

@joshbuddy LGTM, just one typo.

[joshbuddy]

@rittneje fixed, thank you

[joshbuddy]

Looks like some test flakiness?

[rittneje]

@joshbuddy I think there may be something wrong with TestQueryer, and due to an oversight in how it got written, it is not reporting the real issue. Can you update that unit test like so?

for rows.Next() {
    ...
}
if err := rows.Err(); err != nil {
    t.Fatal(err)
}
if n != 3 {
    ...
}

[joshbuddy]

Hey @rittneje, I fixed the underlying test. If you want me to split it off into a separate PR, let me know.

[joshbuddy]

I've moved the test fixes to #1079

[codecov-commenter]

Codecov Report

Merging #1071 (0f9d82e) into master (f92b6bb) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1071   +/-   ##
=======================================
  Coverage   45.96%   45.96%           
=======================================
  Files          11       11           
  Lines        1499     1499           
=======================================
  Hits          689      689           
  Misses        670      670           
  Partials      140      140           

Impacted Files	Coverage Δ
sqlite3.go	52.64% <100.00%> (ø)

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