WIP: Select() using iterator

go.mod

@@ -1,9 +1,11 @@
 module github.com/jmoiron/sqlx
 
-go 1.10
+go 1.27
 
 require (
-	github.com/go-sql-driver/mysql v1.8.1
-	github.com/lib/pq v1.10.9
-	github.com/mattn/go-sqlite3 v1.14.22
+	github.com/go-sql-driver/mysql v1.10.0
+	github.com/lib/pq v1.12.3
+	github.com/mattn/go-sqlite3 v1.14.45
 )
+
+require filippo.io/edwards25519 v1.2.0 // indirect

go.sum

@@ -1,8 +1,16 @@
 filippo.io/edwards25519 v1.1.0 h1:FNf4tywRC1HmFuKW5xopWpigGjJKiJSV0Cqo0cJWDaA=
 filippo.io/edwards25519 v1.1.0/go.mod h1:BxyFTGdWcka3PhytdK4V28tE5sGfRvvvRV7EaN4VDT4=
+filippo.io/edwards25519 v1.2.0 h1:crnVqOiS4jqYleHd9vaKZ+HKtHfllngJIiOpNpoJsjo=
+filippo.io/edwards25519 v1.2.0/go.mod h1:xzAOLCNug/yB62zG1bQ8uziwrIqIuxhctzJT18Q77mc=
 github.com/go-sql-driver/mysql v1.8.1 h1:LedoTUt/eveggdHS9qUFC1EFSa8bU2+1pZjSRpvNJ1Y=
 github.com/go-sql-driver/mysql v1.8.1/go.mod h1:wEBSXgmK//2ZFJyE+qWnIsVGmvmEKlqwuVSjsCm7DZg=
+github.com/go-sql-driver/mysql v1.10.0 h1:Q+1LV8DkHJvSYAdR83XzuhDaTykuDx0l6fkXxoWCWfw=
+github.com/go-sql-driver/mysql v1.10.0/go.mod h1:M+cqaI7+xxXGG9swrdeUIoPG3Y3KCkF0pZej+SK+nWk=
 github.com/lib/pq v1.10.9 h1:YXG7RB+JIjhP29X+OtkiDnYaXQwpS4JEWq7dtCCRUEw=
 github.com/lib/pq v1.10.9/go.mod h1:AlVN5x4E4T544tWzH6hKfbfQvm3HdbOxrmggDNAPY9o=
+github.com/lib/pq v1.12.3 h1:tTWxr2YLKwIvK90ZXEw8GP7UFHtcbTtty8zsI+YjrfQ=
+github.com/lib/pq v1.12.3/go.mod h1:/p+8NSbOcwzAEI7wiMXFlgydTwcgTr3OSKMsD2BitpA=
 github.com/mattn/go-sqlite3 v1.14.22 h1:2gZY6PC6kBnID23Tichd1K+Z0oS6nE/XwU+Vz/5o4kU=
 github.com/mattn/go-sqlite3 v1.14.22/go.mod h1:Uh1q+B4BYcTPb+yiD3kU8Ct7aC0hY9fxUwlHK0RXw+Y=
+github.com/mattn/go-sqlite3 v1.14.45 h1:6KA/spDguL3KV8rnybG7ezSaE4SeMR3KC9VbUoAQaIk=
+github.com/mattn/go-sqlite3 v1.14.45/go.mod h1:pjEuOr8IwzLJP2MfGeTb0A35jauH+C2kbHKBr7yXKVQ=

sqlx.go

@@ -6,6 +6,7 @@ import (
 	"errors"
 	"fmt"
 	"io/ioutil"
+	"iter"
 	"path/filepath"
 	"reflect"
 	"strings"
@@ -320,6 +321,10 @@ func (db *DB) Select(dest interface{}, query string, args ...interface{}) error
 	return Select(db, dest, query, args...)
 }
 
+func (db *DB) SelectIter[T any](query string, args ...interface{}) iter.Seq2[*T, error] {
+	return SelectIter[T](db, query, args...)
+}
+
 // Get using this DB.
 // Any placeholder parameters are replaced with supplied args.
 // An error is returned if the result set is empty.
@@ -434,6 +439,12 @@ func (tx *Tx) Select(dest interface{}, query string, args ...interface{}) error
 	return Select(tx, dest, query, args...)
 }
 
+// SelectIter within a transaction.
+// Any placeholder parameters are replaced with supplied args.
+func (tx *Tx) SelectIter[T any](query string, args ...interface{}) iter.Seq2[*T, error] {
+	return SelectIter[T](tx, query, args...)
+}
+
 // Queryx within a transaction.
 // Any placeholder parameters are replaced with supplied args.
 func (tx *Tx) Queryx(query string, args ...interface{}) (*Rows, error) {
@@ -519,6 +530,12 @@ func (s *Stmt) Select(dest interface{}, args ...interface{}) error {
 	return Select(&qStmt{s}, dest, "", args...)
 }
 
+// SelectIter using the prepared statement.
+// Any placeholder parameters are replaced with supplied args.
+func (s *Stmt) SelectIter[T any](query string, args ...interface{}) iter.Seq2[*T, error] {
+	return SelectIter[T](&qStmt{s}, query, args...)
+}
+
 // Get using the prepared statement.
 // Any placeholder parameters are replaced with supplied args.
 // An error is returned if the result set is empty.
@@ -683,6 +700,52 @@ func Select(q Queryer, dest interface{}, query string, args ...interface{}) erro
 	return scanAll(rows, dest, false)
 }
 
+// SelectIter returns an iterator that executes the query and then starts
+// returning rows of the specific type one by one. When an error is returned
+// iteration stops.
+//
+// Example:
+//
+//	for u, err := range SelectIter[User](db, `SELECT * FROM users ORDER BY id`) {
+//	    if err != nil { ... }
+//	    ...
+//	}
+func SelectIter[T any](q Queryer, query string, args ...interface{}) iter.Seq2[*T, error] {
+	return func(yield func(*T, error) bool) {
+		rows, err := q.Queryx(query, args...)
+		if err != nil {
+			yield(nil, err)
+			return
+		}
+		// We cannot use yield() inside defer, so we Close() the rows manually.
+
+		for rows.Next() {
+			var row T
+			if err := rows.StructScan(&row); err != nil {
+				yield(nil, err)
+
+				// We've already returned a single error, so ignoring Close()
+				// error here.
+				_ = rows.Close()
+				return
+			}
+
+			if !yield(&row, nil) {
+				// Cannot yield again after the iteration has stopped, so ignoring
+				// Close() error here.
+				_ = rows.Close()
+				return
+			}
+		}
+
+		// It's a common mistake to ignore rows.Close() error value, however
+		// it can still happen, so we need to handle it.
+		if err := rows.Close(); err != nil {
+			yield(nil, err)
+		}
+	}
+}
+
 // Get does a QueryRow using the provided Queryer, and scans the resulting row
 // to dest.  If dest is scannable, the result must only have one column.  Otherwise,
 // StructScan is used.  Get will return sql.ErrNoRows like row.Scan would.

sqlx_test.go

@@ -1923,3 +1923,39 @@ func TestSelectReset(t *testing.T) {
 		}
 	})
 }
+
+func TestSelectIter(t *testing.T) {
+	RunWithSchema(defaultSchema, t, func(db *DB, t *testing.T, now string) {
+		loadDefaultFixture(db, t)
+
+		var people []*Person
+		const query = "SELECT * FROM person ORDER BY first_name"
+
+		err := db.Select(&people, query)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if want := 2; len(people) != want {
+			t.Errorf("Expected %d first names, got %d", want, len(people))
+		}
+
+		var peopleIter []*Person
+		for p, err := range db.SelectIter[Person](query) {
+			if err != nil {
+				t.Fatalf("Iteration failed for %s: %v", query, err)
+			}
+
+			peopleIter = append(peopleIter, p)
+		}
+
+		if len(people) != len(peopleIter) {
+			t.Fatalf("SelectIter() returned %d rows, want %d", len(peopleIter), len(people))
+		}
+
+		for i, p := range people {
+			if !reflect.DeepEqual(p, peopleIter[i]) {
+				t.Errorf("SelectIter() %d result is wrong, got %+v, want %+v", i, peopleIter[i], p)
+			}
+		}
+	})
+}