feat: omitempty and omitnil struct tags

[simon-a-j]

There are a couple of open issues which I think would be most elegantly resolved by the introduction of omitempty and/or omitnil struct tags: #174, #234. This PR introduces both tags.

This provides for much greater flexibility when handling partial inserts or updates. For example, we may handle a partial update as a struct of pointers, where null values are not to be updated.

1. omitnil

type PersonUpdate struct {
	Name    *string `db:"name" goqu:"omitnil"`
	Address *string `db:"address" goqu:"omitnil"`
}
address := "Test"
i := item{Address: &testString, Address2: &emptyString}
insertSQL, args, _ := goqu.Insert("items").Rows(i).ToSQL()
fmt.Println(insertSQL, args)

Output before this PR:

INSERT INTO "items" ("address", "name") VALUES ('Test', NULL) []

Output after this PR:

INSERT INTO "items" ("address") VALUES ('Test') []

2. omitempty

type item struct {
	Name    string `db:"name" goqu:"omitempty"`
	Address string `db:"address" goqu:"omitempty"`
}
i := item{Address: "address"}

insertSQL, args, _ := goqu.Insert("items").Rows(i).ToSQL()
fmt.Println(insertSQL, args)

Output before this PR:

INSERT INTO "items" ("address", "name") VALUES ('address', '') []

Output after this PR:

INSERT INTO "items" ("address") VALUES ('address') []

3. Discussion Items

1. I have adjusted the implementation of util.IsEmptyValue. Previously it did NOT return true for zero structs. The new implementation uses reflect.IsZero which returns true for zero structs.
   • The reason for this is that it allows omitempty to work with structs that implement the Valuer interface (like NullString) in the way we'd expect - ie. a Valuer without a value should be omitted.
   • It also allows defaultifempty to work similarly with these structs, which will change the behaviour of existing code if anyone annotated Valuer struct fields previously.
   • I can't see a good reason util.IsEmptyValue was previously implemented as it was, but am very open to feedback if I missed something or if the retrospective behaviour change is undesirable.
2. The *_example_test.go tests are more extensive than the examples included in documentation. I thought this was the cleanest place to put the extra tests.

[simon-a-j]

@doug-martin I planned to run CI workflows before marking ready to review, so if you are happy to approve running workflows that would be awesome :)

[codecov]

Codecov Report

Merging #309 (293c6da) into master (a7630f7) will increase coverage by 0.00%.
The diff coverage is 94.73%.

@@           Coverage Diff           @@
##           master     #309   +/-   ##
=======================================
  Coverage   96.89%   96.90%           
=======================================
  Files          62       62           
  Lines        3477     3485    +8     
=======================================
+ Hits         3369     3377    +8     
  Misses         92       92           
  Partials       16       16           

Flag	Coverage Δ
unittests	96.90% <94.73%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
exp/record.go	87.09% <92.30%> (+1.91%)	⬆️
internal/util/column_map.go	100.00% <100.00%> (ø)
internal/util/reflect.go	98.95% <100.00%> (-0.09%)	⬇️
exp/exp.go	71.42% <0.00%> (ø)
insert_dataset.go	100.00% <0.00%> (ø)
exp/insert_clauses.go	100.00% <0.00%> (ø)
sqlgen/insert_sql_generator.go	100.00% <0.00%> (ø)
exp/bool.go	93.33% <0.00%> (+0.11%)	⬆️

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[simon-a-j]

I feel this is in reasonable shape to review. The coverage is down due to an existing uncovered path which I think should be unreachable. Happy to resolve if preferable, but it means we need to expose that logic outside the package and I’m not sure it’s worthwhile.

[alyhegazy]

Any updates on this? Would be a useful feature to get this merged.

[pravinchandar]

Would be keen to know the progress on this?

[dvaldivia]

This should be taken imo

[iredmail]

Dear @funkyshu

Do you have time to take a look at other PRs? Seems this project doesn't have any other maintainers, and no others have privilege to update repo.