Add sql iteration package

README.md

@@ -2,6 +2,7 @@ A collection of Go libraries:
 * [errors](https://github.com/Zamony/go/tree/main/errors)  - errors with stacktraces;
 * [sync](https://github.com/Zamony/go/tree/main/sync) - additional synchronization primitives;
 * [zap](https://github.com/Zamony/go/tree/main/zap) - structured logging;
+* [sqliter](https://github.com/Zamony/go/tree/main/sqliter) - iterator for sql queries;
 * [golimit](https://github.com/Zamony/go/tree/main/golimit) - simple rate limiter;
 * [toast](https://github.com/Zamony/go/tree/main/toast) - test helpers;
 * [squll](https://github.com/Zamony/go/tree/main/squll) - sql templating;

sqliter/go.mod

@@ -0,0 +1,3 @@
+module github.com/Zamony/go/sqliter
+
+go 1.23

sqliter/sqliter.go

@@ -0,0 +1,54 @@
+/*
+Package sqliter provides utilities for querying SQL databases using iterators.
+
+It defines a Querier interface for executing SQL queries and a Query function
+that returns an iterator over the results of a query. The iterator yields
+values of a specified type and any errors encountered during the iteration.
+*/
+
+package sqliter
+
+import (
+	"context"
+	"database/sql"
+	"iter"
+)
+
+// Row represents a single row returned by a query.
+type Row interface {
+	// Scan copies the columns from the current row into the values pointed to by dest.
+	Scan(dest ...any) error
+}
+
+// Querier is an interface for executing SQL queries.
+type Querier interface {
+	// QueryContext executes a query with the given context and arguments,
+	// returning the result set as *sql.Rows.
+	QueryContext(ctx context.Context, query string, args ...any) (*sql.Rows, error)
+}
+
+// Query executes a query with the provided context and returns an iterator over the results.
+// The scanner function is used to convert each row into a value of type T.
+// If an error occurs during the query execution, the iterator will yield an error as the second return value.
+func Query[T any](ctx context.Context, querier Querier, scanner func(row Row) (T, error), query string, args ...any) iter.Seq2[T, error] {
+	rows, err := querier.QueryContext(ctx, query, args...)
+	if err != nil {
+		return func(yield func(T, error) bool) {
+			var t T
+			yield(t, err) // Yield an error if the query fails
+		}
+	}
+	return func(yield func(T, error) bool) {
+		defer rows.Close() // Ensure rows are closed after iteration
+		for rows.Next() {
+			v, err := scanner(rows) // Scan the row into a value of type T
+			if !yield(v, err) {     // Yield the value and error
+				return
+			}
+		}
+		if err := rows.Err(); err != nil {
+			var t T
+			yield(t, err) // Yield an error if there was an issue during iteration
+		}
+	}
+}