🐛 fix(dbio): handle nil connection instance

- added error handling for nil connection instance in Prepare and ExecContext methods
- improved error messages for better debugging
- updated Dataset struct to include json tags for better serialization

core/dbio/database/database.go

@@ -1070,8 +1070,10 @@ func (conn *BaseConn) Rollback() (err error) {
 func (conn *BaseConn) Prepare(query string) (stmt *sql.Stmt, err error) {
 	if conn.tx != nil {
 		stmt, err = conn.tx.Prepare(query)
-	} else {
+	} else if conn.db != nil {
 		stmt, err = conn.db.PrepareContext(conn.Context().Ctx, query)
+	} else {
+		err = g.Error("no connection instance")
 	}
 	if err != nil {
 		err = g.Error(err, "could not prepare statement")
@@ -1125,9 +1127,11 @@ func (conn *BaseConn) ExecContext(ctx context.Context, q string, args ...interfa
 	if conn.tx != nil {
 		result, err = conn.tx.ExecContext(ctx, q, args...)
 		q = q + noDebugKey // just to not show twice the sql in error since tx does
-	} else {
+	} else if conn.db != nil {
 		conn.LogSQL(q, args...)
 		result, err = conn.db.ExecContext(ctx, q, args...)
+	} else {
+		err = g.Error("no connection instance")
 	}
 	if err != nil {
 		if strings.Contains(q, noDebugKey) {

core/dbio/iop/dataset.go

@@ -20,15 +20,15 @@ import (
 
 // Dataset is a query returned dataset
 type Dataset struct {
-	Result        *sqlx.Rows
-	Columns       Columns
-	Rows          [][]interface{}
-	SQL           string
-	Duration      float64
-	Sp            *StreamProcessor
-	Inferred      bool
-	SafeInference bool
-	NoDebug       bool
+	Result        *sqlx.Rows       `json:"-"`
+	Columns       Columns          `json:"columns"`
+	Rows          [][]any          `json:"rows"`
+	SQL           string           `json:"sql"`
+	Duration      float64          `json:"duration"`
+	Sp            *StreamProcessor `json:"-"`
+	Inferred      bool             `json:"inferred"`
+	SafeInference bool             `json:"safe_inference"`
+	NoDebug       bool             `json:"no_debug"`
 }
 
 // NewDataset return a new dataset