initial MVP for oblast.Select()

7 files changed, 232 insertions, 1 deletions

diff --git a/benchmark/benchmark_test.go b/benchmark/benchmark_test.go
new file mode 100644
index 0000000..c08361e
--- /dev/null
+++ b/benchmark/benchmark_test.go
@@ -0,0 +1,131 @@
+// SPDX-FileCopyrightText: 2026 Stefan Majewsky <majewsky@gmx.net>
+// SPDX-License-Identifier: Apache-2.0
+
+package main_test
+
+import (
+	"crypto/sha256"
+	"database/sql"
+	"fmt"
+	"strconv"
+	"testing"
+
+	"github.com/go-gorp/gorp/v3"
+	_ "github.com/mattn/go-sqlite3"
+	"go.xyrillian.de/oblast"
+)
+
+func BenchmarkSelect(b *testing.B) {
+	const (
+		totalRecordCount    = 10000
+		selectedRecordCount = 1
+	)
+
+	db, err := sql.Open("sqlite3", "file:foobar?mode=memory&cache=shared")
+	if err != nil {
+		b.Fatal(err)
+	}
+
+	// fill in some random-looking, but deterministic data
+	_, err = db.Exec(`CREATE TABLE entries (id INTEGER, message TEXT)`)
+	if err != nil {
+		b.Fatal(err)
+	}
+	stmt, err := db.Prepare(`INSERT INTO entries (id, message) VALUES (?, ?)`)
+	if err != nil {
+		b.Fatal(err)
+	}
+	for idx := range totalRecordCount {
+		buf := sha256.Sum256([]byte(strconv.Itoa(idx)))
+		_, err = stmt.Exec(idx, fmt.Sprintf("sha256:%x", buf[:]))
+		if err != nil {
+			b.Fatal(err)
+		}
+	}
+	err = stmt.Close()
+	if err != nil {
+		b.Fatal(err)
+	}
+
+	// prepare the functions that will be benched
+	odb := oblast.NewDB(db, oblast.SqliteDialect())
+	gdb := gorp.DbMap{Db: db, Dialect: gorp.SqliteDialect{}}
+	type record struct {
+		ID      int    `db:"id"`
+		Message string `db:"message"`
+	}
+	query := `SELECT * FROM entries WHERE id < ` + strconv.Itoa(selectedRecordCount)
+
+	selectWithOblast := func(b *testing.B) {
+		records, err := oblast.Select[record](b.Context(), odb, query)
+		if err != nil {
+			b.Error(err)
+		}
+		if len(records) != selectedRecordCount {
+			b.Errorf("expected %d, but got %d records", selectedRecordCount, len(records))
+		}
+	}
+
+	selectWithGorp := func(b *testing.B) {
+		var records []record
+		_, err := gdb.Select(&records, query)
+		if err != nil {
+			b.Error(err)
+		}
+		if len(records) != selectedRecordCount {
+			b.Errorf("expected %d, but got %d records", selectedRecordCount, len(records))
+		}
+	}
+
+	selectWithSqlite := func(b *testing.B) {
+		var count int64
+		rows, err := db.Query(query)
+		if err != nil {
+			b.Error(err)
+		}
+		var (
+			id      int64
+			message string
+		)
+		for rows.Next() {
+			err := rows.Scan(&id, &message)
+			if err != nil {
+				b.Error(err)
+			}
+			if id != 20000 && message != "" { // always true; ensures that values are not optimized away
+				count++
+			}
+		}
+		err = rows.Close()
+		if err != nil {
+			b.Error(err)
+		}
+		if count != selectedRecordCount {
+			b.Errorf("expected %d, but got %d records", selectedRecordCount, count)
+		}
+	}
+
+	// run once to prewarm caches
+	selectWithOblast(b)
+	selectWithGorp(b)
+	if b.Failed() {
+		b.FailNow()
+	}
+
+	// run actual benchmark
+	b.Run("via Gorp", func(b *testing.B) {
+		for range b.N {
+			selectWithGorp(b)
+		}
+	})
+	b.Run("via Oblast", func(b *testing.B) {
+		for range b.N {
+			selectWithOblast(b)
+		}
+	})
+	b.Run("just SQLite", func(b *testing.B) {
+		for range b.N {
+			selectWithSqlite(b)
+		}
+	})
+}
diff --git a/benchmark/go.mod b/benchmark/go.mod
new file mode 100644
index 0000000..01e8126
--- /dev/null
+++ b/benchmark/go.mod
@@ -0,0 +1,9 @@
+module go.xyrillian.de/oblast/benchmark
+
+go 1.26.0
+
+require (
+	github.com/go-gorp/gorp/v3 v3.1.0
+	github.com/mattn/go-sqlite3 v1.14.42
+	go.xyrillian.de/oblast v0.0.0-20260410125639-bce3df549ff4
+)
diff --git a/benchmark/go.sum b/benchmark/go.sum
new file mode 100644
index 0000000..e05abdd
--- /dev/null
+++ b/benchmark/go.sum
@@ -0,0 +1,20 @@
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/go-gorp/gorp/v3 v3.1.0 h1:ItKF/Vbuj31dmV4jxA1qblpSwkl9g1typ24xoe70IGs=
+github.com/go-gorp/gorp/v3 v3.1.0/go.mod h1:dLEjIyyRNiXvNZ8PSmzpt1GsWAUK8kjVhEpjH8TixEw=
+github.com/go-sql-driver/mysql v1.6.0 h1:BCTh4TKNUYmOmMUcQ3IipzF5prigylS7XXjEkfCHuOE=
+github.com/go-sql-driver/mysql v1.6.0/go.mod h1:DCzpHaOWr8IXmIStZouvnhqoel9Qv2LBy8hT2VhHyBg=
+github.com/lib/pq v1.10.7 h1:p7ZhMD+KsSRozJr34udlUrhboJwWAgCg34+/ZZNvZZw=
+github.com/lib/pq v1.10.7/go.mod h1:AlVN5x4E4T544tWzH6hKfbfQvm3HdbOxrmggDNAPY9o=
+github.com/mattn/go-sqlite3 v1.14.42 h1:MigqEP4ZmHw3aIdIT7T+9TLa90Z6smwcthx+Azv4Cgo=
+github.com/mattn/go-sqlite3 v1.14.42/go.mod h1:pjEuOr8IwzLJP2MfGeTb0A35jauH+C2kbHKBr7yXKVQ=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/poy/onpar v1.1.2 h1:QaNrNiZx0+Nar5dLgTVp5mXkyoVFIbepjyEoGSnhbAY=
+github.com/poy/onpar v1.1.2/go.mod h1:6X8FLNoxyr9kkmnlqpK6LSoiOtrO6MICtWwEuWkLjzg=
+github.com/stretchr/testify v1.8.0 h1:pSgiaMZlXftHpm5L7V1+rVB+AZJydKsMxsQBIJw4PKk=
+github.com/stretchr/testify v1.8.0/go.mod h1:yNjHg4UonilssWZ8iaSj1OCr/vHnekPRkoO+kdMU+MU=
+go.xyrillian.de/oblast v0.0.0-20260410125639-bce3df549ff4 h1:MJpcBoNsrY4e/eRpYfz1Gllc3aqIjwFxSPSyKToa+mQ=
+go.xyrillian.de/oblast v0.0.0-20260410125639-bce3df549ff4/go.mod h1:lo6ekGOHTID0KeSWhNQV1gjYJ2BfhXgenUEBNBnZkBM=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
diff --git a/benchmark/main.go b/benchmark/main.go
new file mode 100644
index 0000000..e80c2cd
--- /dev/null
+++ b/benchmark/main.go
@@ -0,0 +1,8 @@
+// SPDX-FileCopyrightText: 2026 Stefan Majewsky <majewsky@gmx.net>
+// SPDX-License-Identifier: Apache-2.0
+
+package main
+
+func main() {
+	panic("run with `go test -bench`")
+}
diff --git a/db.go b/db.go
index a511d6f..8f1a050 100644
--- a/db.go
+++ b/db.go
@@ -6,6 +6,7 @@ package oblast
 import (
 	"context"
 	"database/sql"
+	"fmt"
 	"reflect"
 	"sync"
 )
@@ -26,9 +27,58 @@ func NewDB(db *sql.DB, dialect Dialect) *DB {
 	}
 }
 
+// TODO: remove
 func Keks[T IsTable](ctx context.Context, db *DB) error {
 	_, err := db.getPlan(reflect.TypeFor[T]())
 	return err
 }
 
-// TODO: Begin() -> custom Tx type
+// TODO: Begin() -> custom Tx type; add interface to allow Select() et all to take either *DB or *Tx
+
+func Select[T any](ctx context.Context, db *DB, query string, args ...any) ([]T, error) {
+	// TODO: minimize function body to avoid binary size blowup from monomorphization
+	// TODO: catch error from rows.Close(), if any
+	// TODO: add context to errors
+
+	plan, err := db.getPlan(reflect.TypeFor[T]())
+	if err != nil {
+		return nil, err
+	}
+	rows, err := db.Query(query, args...)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	columnNames, err := rows.Columns()
+	if err != nil {
+		return nil, err
+	}
+	indexes := make([][]int, len(columnNames))
+	for idx, columnName := range columnNames {
+		var ok bool
+		indexes[idx], ok = plan.IndexByColumnName[columnName]
+		if !ok {
+			var zero T
+			return nil, fmt.Errorf("result has column %q in position %d, but no field in %T has `db:%[1]q`",
+				columnName, idx, zero)
+		}
+	}
+
+	var result []T
+	slots := make([]any, len(indexes))
+	for rows.Next() {
+		var target T
+		rvalue := reflect.ValueOf(&target).Elem()
+		for idx, index := range indexes {
+			slots[idx] = rvalue.FieldByIndex(index).Addr().Interface()
+		}
+		err := rows.Scan(slots...)
+		if err != nil {
+			return nil, err
+		}
+		result = append(result, target)
+	}
+
+	return result, nil
+}
diff --git a/go.work b/go.work
new file mode 100644
index 0000000..0f59ee6
--- /dev/null
+++ b/go.work
@@ -0,0 +1,6 @@
+go 1.26.0
+
+use (
+	.
+	./benchmark
+)
diff --git a/go.work.sum b/go.work.sum
new file mode 100644
index 0000000..847440b
--- /dev/null
+++ b/go.work.sum
@@ -0,0 +1,7 @@
+github.com/fatih/color v1.13.0/go.mod h1:kLAiJbzzSOZDVNGyDpeOxJ47H46qBXwg5ILebYFFOfk=
+github.com/kr/pretty v0.3.1/go.mod h1:hoEshYVHaxMs3cyo3Yncou5ZscifuDolrwPKZanG3xk=
+github.com/mattn/go-colorable v0.1.13/go.mod h1:7S9/ev0klgBDR4GtXTXX8a3vIGJpMovkB8vQcUbaXHg=
+github.com/mattn/go-isatty v0.0.16/go.mod h1:kYGgaQfpe5nmfYZH+SKPsOc2e4SrIfOl2e/yFXSvRLM=
+github.com/nelsam/hel/v2 v2.3.3/go.mod h1:1ZTGfU2PFTOd5mx22i5O0Lc2GY933lQ2wb/ggy+rL3w=
+golang.org/x/sys v0.0.0-20221013171732-95e765b1cc43/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c/go.mod h1:JHkPIbrfpd72SG/EVd6muEfDQjcINNoR0C8j2r3qZ4Q=