ooooo generic db.Query, db.QueryOne

src/db/db.go

@@ -3,14 +3,86 @@ package db
 import (
 	"context"
 	"database/sql"
+	"encoding/json"
+	"fmt"
 )
 
-func QueryOne(ctx context.Context, q string, args ...any) error {
-	return with(ctx, func(db *sql.DB) error {
-		row := db.QueryRowContext(ctx, q, args...)
-      TODO generic and return value
-		return row.Err()
+func QueryOne[T any](ctx context.Context, q string, args ...any) (T, error) {
+	results, err := Query[T](ctx, q, args...)
+	if err != nil || len(results) == 0 {
+		var a T
+		return a, err
+	}
+
+	if len(results) > 1 {
+		var a T
+		return a, fmt.Errorf("expected exactly 1 result but got %d", len(results))
+	}
+
+	return results[0], nil
+}
+
+func Query[T any](ctx context.Context, q string, args ...any) ([]T, error) {
+	var result []T
+
+	var a T
+	var m map[string]any
+	b, _ := json.Marshal(a)
+	if err := json.Unmarshal(b, &m); err != nil {
+		return nil, fmt.Errorf("%T is not map-like: %w", a, err)
+	}
+	scanners := func(columns []string) ([]any, error) {
+		s := make([]any, len(columns))
+		for i, k := range columns {
+			v, ok := m[k]
+			if !ok {
+				return nil, fmt.Errorf("cannot scan column %s to %T (%+v)", k, a, m)
+			}
+			s[i] = &v
+		}
+		return s, nil
+	}
+
+	err := with(ctx, func(db *sql.DB) error {
+		rows, err := db.QueryContext(ctx, q, args...)
+		if err != nil {
+			return err
+		}
+		defer rows.Close()
+
+		columns, err := rows.Columns()
+		if err != nil {
+			return err
+		}
+
+		for rows.Next() {
+			scanners, err := scanners(columns)
+			if err != nil {
+				return err
+			}
+
+			if err := rows.Scan(scanners...); err != nil {
+				return err
+			}
+
+			m := map[string]any{}
+			for i, column := range columns {
+				m[column] = scanners[i]
+			}
+
+			var a T
+			if b, err := json.Marshal(m); err != nil {
+				return err
+			} else if err := json.Unmarshal(b, &a); err != nil {
+				return err
+			} else {
+				result = append(result, a)
+			}
+		}
+
+		return rows.Err()
 	})
+	return result, err
 }
 
 func Exec(ctx context.Context, q string, args ...any) error {

src/db/db_test.go

@@ -28,17 +28,17 @@ func TestDB(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	var result struct {
-		K string
+	type result struct {
+		K string `json:"k"`
 	}
 	if got, err := db.QueryOne[result](ctx, `SELECT k FROM test WHERE k='a'`); err != nil {
-		t.Errorf("failed query one: %w", err)
+		t.Errorf("failed query one: %v", err)
 	} else if got.K != "a" {
 		t.Errorf("bad query one: %+v", got)
 	}
 
 	if gots, err := db.Query[result](ctx, `SELECT k FROM test`); err != nil {
-		t.Errorf("failed query: %w", err)
+		t.Errorf("failed query: %v", err)
 	} else if len(gots) != 2 {
 		t.Errorf("expected 2 but got %d gots", len(gots))
 	} else if gots[0].K != "a" {