reduce function body of Select()

2 files changed, 46 insertions, 18 deletions

diff --git a/internal/plan.go b/internal/plan.go
index 8fc24d8..f738278 100644
--- a/internal/plan.go
+++ b/internal/plan.go
@@ -46,9 +46,16 @@ var (
 
 // BuildPlan creates a new plan for the given struct type.
 func BuildPlan(t reflect.Type, dialect Dialect) (Plan, error) {
+	p, err := buildPlan(t, dialect)
+	if err != nil {
+		return Plan{}, fmt.Errorf("cannot use type %s.%s for queries: %w", t.PkgPath(), t.Name(), err)
+	}
+	return p, nil
+}
+
+func buildPlan(t reflect.Type, dialect Dialect) (Plan, error) {
 	if t.Kind() != reflect.Struct {
-		return Plan{}, fmt.Errorf("expected record type to be a struct, but got kind %s (full type: %s.%s)",
-			t.Kind(), t.PkgPath(), t.Name())
+		return Plan{}, fmt.Errorf("expected struct type, but got kind %s", t.Kind().String())
 	}
 
 	var p = Plan{
diff --git a/query.go b/query.go
index 95c1f59..03b87b6 100644
--- a/query.go
+++ b/query.go
@@ -4,8 +4,11 @@
 package oblast
 
 import (
+	"database/sql"
 	"fmt"
 	"reflect"
+
+	"go.xyrillian.de/oblast/internal"
 )
 
 func Select[T any](db *DB, query string, args ...any) ([]T, error) {
@@ -17,27 +20,12 @@ func Select[T any](db *DB, query string, args ...any) ([]T, error) {
 	if err != nil {
 		return nil, err
 	}
-	rows, err := db.Query(query, args...)
+	rows, indexes, err := db.startQuery(plan, 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() {
@@ -55,3 +43,36 @@ func Select[T any](db *DB, query string, args ...any) ([]T, error) {
 
 	return result, nil
 }
+
+func (db *DB) startQuery(plan internal.Plan, query string, args ...any) (rows *sql.Rows, indexes [][]int, err error) {
+	rows, err = db.Query(query, args...)
+	if err != nil {
+		return nil, nil, err
+	}
+	defer func() {
+		if err != nil {
+			closeErr := rows.Close()
+			if closeErr != nil {
+				err = fmt.Errorf("%w (additional error during rows.Close: %s)", err, closeErr.Error())
+			}
+		}
+	}()
+
+	columnNames, err := rows.Columns()
+	if err != nil {
+		return nil, nil, err
+	}
+	indexes = make([][]int, len(columnNames))
+	for idx, columnName := range columnNames {
+		var ok bool
+		indexes[idx], ok = plan.IndexByColumnName[columnName]
+		if !ok {
+			return nil, nil, fmt.Errorf(
+				"result has column %q in position %d, but no field in record type has `db:%[1]q`",
+				columnName, idx,
+			)
+		}
+	}
+
+	return rows, indexes, nil
+}