You had me at "ruins mongodb", actually just "ruins'. On Wed, Jun 8, 2016 at 9:04 PM, roger peppe <roger.pe...@canonical.com> wrote: > This is also relevant (but probably only for larger documents): > > https://jeremywsherman.com/blog/2013/04/23/key-reordering-ruins-mongodb/ > > Another reason to avoid entire-subdocument matches. > > On 8 June 2016 at 10:42, Menno Smits <menno.sm...@canonical.com> wrote: >> >> >> On 8 June 2016 at 21:05, Tim Penhey <tim.pen...@canonical.com> wrote: >>> >>> Hi folks, >>> >>> tl;dr: not use structs in transaction asserts >>> >>> ... >>> >>> The solution is to not use a field struct equality, even though it is easy >>> to write, but to use the dotted field notation to check the embedded field >>> values. >> >> >> >> To give a more concrete example, asserting on a embedded document field like >> this is problematic: >> >> ops := []txn.Op{{ >> C: "collection", >> Id: ..., >> Assert: bson.D{{"some-field", Thing{A: "foo", B: 99}}}, >> Update: ... >> } >> >> Due to the way mgo works[1], the document the transaction operation is >> asserting against may have been written with A and B in reverse order, or >> the Thing struct in the Assert may have A and B swapped by the time it's >> used. Either way, the assertion will fail randomly. >> >> The correct approach is to express the assertion like this: >> >> ops := []txn.Op{{ >> C: "collection", >> Id: ..., >> Assert: bson.D{ >> {"some-field.A", "foo"}, >> {"some-field.B", 99}, >> }, >> Update: ... >> } >> >> or this: >> >> ops := []txn.Op{{ >> C: "collection", >> Id: ..., >> Assert: bson.M{ >> "some-field.A": "foo", >> "some-field.B": 99, >> }, >> Update: ... >> } >> >>> >>> Yet another thing to add to the list of things to check when doing >>> reviews. >> >> >> I think we can go a bit further and error on attempts to use structs for >> comparison in txn.Op asserts in Juju's txn layers in state. Just as we >> already do some munging and checking of database operations to ensure >> correct multi-model behaviour, we should be able to do this same for this >> issue and prevent it from happening again. >> >> - Menno >> >> [1] If transaction operations are loaded and used from the DB (more likely >> under load when multiple runners are acting concurrently), the Insert, >> Update and Assert fields are loaded as bson.M (this is what the bson >> Unmarshaller does for interface{} typed fields). Once this happens field >> ordering is lost. >> >> >> >> >> -- >> Juju-dev mailing list >> Juju-dev@lists.ubuntu.com >> Modify settings or unsubscribe at: >> https://lists.ubuntu.com/mailman/listinfo/juju-dev >> > > -- > Juju-dev mailing list > Juju-dev@lists.ubuntu.com > Modify settings or unsubscribe at: > https://lists.ubuntu.com/mailman/listinfo/juju-dev
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