nettools/pg/pg.go

package pgUtils

import (
	"context"
	"errors"
	"github.com/jackc/pgx/v5"
	"github.com/jackc/pgx/v5/pgxpool"
	reflectUtils "nettools/reflect"
)

var (
	ErrEntityNotFound      = errors.New("entity not found")
	ErrTooManyRows         = errors.New("too many rows")
	ErrEntityAlreadyExists = errors.New("entity already exists")
	ErrNoDstFields         = errors.New("no destination fields")
)

type PgxQuerier interface {
	Query(ctx context.Context, sql string, args ...any) (pgx.Rows, error)
}

// Select executes query on a provided querier and tries to parse db response into antit
// Works only with objects
//
// Usage:
//
//	type User struct {
//	  Id   int    `db:"id"`
//	  Name string `db:"name"`
//	}
//
//	db := pgx.Connect(context.Background(), "<url>")
//	users, err := pgUtils.Select[User](context.Background(), db, "SELECT id, name FROM users")
func Select[T any](ctx context.Context, db PgxQuerier, query string, args ...any) (out []*T, err error) {
	rows, err := db.Query(ctx, query, args)
	if err != nil {
		switch {
		case errors.Is(err, pgx.ErrNoRows):
			err = ErrEntityNotFound
		} // TODO: extend cases
		return nil, err
	}

	// Get column names
	columns := make([]string, len(rows.FieldDescriptions()))
	for i, fd := range rows.FieldDescriptions() {
		columns[i] = fd.Name
	}
	itemFieldPtrs := make([]any, len(columns))
	out = []*T{}

	defer rows.Close()
	for rows.Next() {
		item := new(T)
		dstItemPtrsMap, err := reflectUtils.GetEntityPtrs(item, "db")
		if err != nil {
			return nil, err
		}
		for i, columnName := range columns {
			itemFieldPtrs[i] = dstItemPtrsMap[columnName]
		}
		if len(itemFieldPtrs) == 0 {
			return nil, ErrNoDstFields
		}
		if err = rows.Scan(itemFieldPtrs...); err != nil {
			return out, err
		}
		out = append(out, item)
	}
	return out, err
}

// Tx creates new transaction. Cancels it if returned not nil err
func Tx(ctx context.Context, db *pgxpool.Pool, exec func(ctx context.Context, tx pgx.Tx) error) error {
	tx, err := db.Begin(ctx)
	if err != nil {
		return err
	}
	err = exec(ctx, tx)
	if err != nil {
		_ = tx.Rollback(ctx)
		return err
	}
	return tx.Commit(ctx)
}