feat: add delete, context, and tx helpers

Add Delete/DeleteAffected, context-aware CRUD helpers, WithTx, ContainsCol,
and queryReturning deduplication for returning statements.

Co-authored-by: Cursor <cursoragent@cursor.com>

jet_columns_test.go

@@ -0,0 +1,105 @@
+package dbx
+
+import (
+	"context"
+	"database/sql"
+	"errors"
+	"testing"
+
+	"github.com/go-jet/jet/v2/mysql"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	_ "modernc.org/sqlite"
+)
+
+func TestContainsCol(t *testing.T) {
+	colA := mysql.StringColumn("a")
+	colB := mysql.StringColumn("b")
+	cols := ColumnList{colA, colB}
+
+	assert.True(t, ContainsCol(cols, colA))
+	assert.False(t, ContainsCol(cols, mysql.StringColumn("c")))
+}
+
+func TestNormalCols_ExcludesTimestamp(t *testing.T) {
+	name := mysql.StringColumn("name")
+	ts := mysql.TimestampColumn("updated_at")
+	cols := NormalCols(name, ts)
+
+	require.Len(t, cols, 1)
+	assert.Equal(t, name, cols[0])
+}
+
+type mockTxDB struct {
+	beginErr error
+}
+
+func (m *mockTxDB) Query(string, ...any) (*sql.Rows, error) { return nil, nil }
+
+func (m *mockTxDB) QueryContext(context.Context, string, ...any) (*sql.Rows, error) {
+	return nil, nil
+}
+
+func (m *mockTxDB) Exec(string, ...any) (sql.Result, error) { return nil, nil }
+
+func (m *mockTxDB) ExecContext(context.Context, string, ...any) (sql.Result, error) {
+	return nil, nil
+}
+
+func (m *mockTxDB) Begin() (*sql.Tx, error) {
+	if m.beginErr != nil {
+		return nil, m.beginErr
+	}
+	return &sql.Tx{}, nil
+}
+
+func TestWithTx_ReturnsFnError(t *testing.T) {
+	db := openTestDB(t)
+
+	wantErr := errors.New("fn failed")
+	err := WithTx(context.Background(), db, func(_ *sql.Tx) error {
+		return wantErr
+	})
+	assert.ErrorIs(t, err, wantErr)
+}
+
+func TestWithTx_CommitsOnSuccess(t *testing.T) {
+	db := openTestDB(t)
+	called := false
+
+	err := WithTx(context.Background(), db, func(_ *sql.Tx) error {
+		called = true
+		return nil
+	})
+	require.NoError(t, err)
+	assert.True(t, called)
+}
+
+func openTestDB(t *testing.T) *sql.DB {
+	t.Helper()
+	db, err := sql.Open("sqlite", ":memory:")
+	require.NoError(t, err)
+	t.Cleanup(func() { _ = db.Close() })
+	return db
+}
+
+func TestWithTx_CancelledContext(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel()
+
+	err := WithTx(ctx, &mockTxDB{}, func(_ *sql.Tx) error {
+		return nil
+	})
+	assert.ErrorIs(t, err, context.Canceled)
+}
+
+func TestWithTx_BeginError(t *testing.T) {
+	wantErr := errors.New("begin failed")
+	err := WithTx(context.Background(), &mockTxDB{beginErr: wantErr}, func(_ *sql.Tx) error {
+		return nil
+	})
+	assert.ErrorIs(t, err, wantErr)
+}
+
+var _ QueryExecTx = (*mockTxDB)(nil)