fix: handle invalid value on fieldByIndex

[EllaFoxo]

When using deep Relation() with Scan(ctx), if the value we're scanning is invalid (usually zero), then bun currently panics when attempting v.Field(idx)

Let's handle that correctly before trying to apply it.

[vmihailenco]

Thanks! Any chance you can add a test or demonstrate how to reproduce this?

[EllaFoxo]

Shall do that next week on my midsummer break! Things have been busy; sorry for the delayed reply

[vmihailenco]

@tinyfluffs thank you in advance!

[lakkinzimusic]

Hello! Is it possible to hope that this PR will get into the release?

[vmihailenco]

We are waiting for a test that demonstrates why we need this PR. @lakkinzimusic perhaps you have one?

[nilsocket]

We are waiting for a test that demonstrates why we need this PR. @lakkinzimusic perhaps you have one?

	"context"
	"database/sql"
	"encoding/json"
	"fmt"
	"log"

	"github.com/uptrace/bun"
	"github.com/uptrace/bun/dialect/sqlitedialect"
	"github.com/uptrace/bun/driver/sqliteshim"
	"github.com/uptrace/bun/extra/bundebug"
)

func main() {
	ctx := context.Background()

	// Open an in-memory SQLite database.
	sqlite, err := sql.Open(sqliteshim.ShimName, "file::memory:?cache=shared")
	if err != nil {
		panic(err)
	}

	// Create a Bun db on top of it.
	db := bun.NewDB(sqlite, sqlitedialect.New())

	// Print all queries to stdout.
	db.AddQueryHook(bundebug.NewQueryHook(bundebug.WithVerbose(true)))

	// create and insert data
	db.NewCreateTable().Model((*SampleTable)(nil)).Exec(ctx)
	db.NewInsert().Model(&Data).Exec(ctx)

	var st []SampleTable

	err = db.NewSelect().Model(&st).
		Relation("FirstChild").
		Relation("FirstChild.FirstChild").
		Scan(ctx)
	if err != nil {
		log.Println(err)
	}

	res, _ := json.MarshalIndent(st, "", "  ")
	fmt.Println(string(res))
}

type SampleTable struct {
	bun.BaseModel `bun:"table:sample_table"`
	ID            int `bun:",autoincrement,pk"`
	FirstChildID  int
	FirstChild    *SampleTable `bun:"rel:has-one,join:first_child_id=id"`
}

var Data = []SampleTable{
	{FirstChildID: 0},
}

[nilsocket]

Hi @vmihailenco , above I have pasted the reproducible program.

I'm facing the similar problem.

I think it's better to check for m.struct.IsValid() in m.scanColumn() along with m.isNil(), before calling field.ScanValue().

Something like this:

if !m.strct.IsValid() || (src == nil && m.isNil()) {
    return true, nil
}

Thank you.

[vmihailenco]

@nilsocket this is what I get when I run your program

[bun]  10:51:32.521   CREATE TABLE           1.07ms  CREATE TABLE "sample_table" ("id" INTEGER NOT NULL, "first_child_id" INTEGER, PRIMARY KEY ("id"))
[bun]  10:51:32.521   INSERT                  143µs  INSERT INTO "sample_table" ("first_child_id") VALUES (0) RETURNING "id"
[bun]  10:51:32.521   SELECT                  132µs  SELECT "sample_table"."id", "sample_table"."first_child_id", "first_child"."id" AS "first_child__id", "first_child"."first_child_id" AS "first_child__first_child_id", "first_child__first_child"."id" AS "first_child__first_child__id", "first_child__first_child"."first_child_id" AS "first_child__first_child__first_child_id" FROM "sample_table" LEFT JOIN "sample_table" AS "first_child" ON ("first_child"."id" = "sample_table"."first_child_id") LEFT JOIN "sample_table" AS "first_child__first_child" ON ("first_child__first_child"."id" = "first_child"."first_child_id")
[
  {
    "ID": 1,
    "FirstChildID": 0,
    "FirstChild": null
  }
]

Is there anything worng?