perl – 如何在DBIx :: Class中定义和使用many_to_many关系？

book        book_language       language
=====  <->> ============== <<-> ========
bookID      book_languageID     languageID
title       bookID              language
            languageID

使用DBIx :: Class :: Schema :: Loader我生成了schema,其中有相应的Result类：

Book
BookLanguage
Language

由于某些原因,Loader没有检测到这些表之间的many_to_many关系,所以我在Language类中自己定义了这样的关系：

package R::RMT::Result::Language;
...
__PACKAGE__->many_to_many('books' => 'book_language_rel','bookid_rel');

在Book类中：

package R::RMT::Result::Book;
...
__PACKAGE__->many_to_many('languages' => 'book_language_rel','languageid_rel');

现在我希望能够访问所有相关语言：

my $dsn = "DBI:mysql:database=rkBook";
my $schema = R::RMT->connect( $dsn,'user','pwd' );

my $book_rs = $schema->resultset('Book');
say $book_rs->languages();

但是我得到了错误：

Can't locate object method "languages" via package "DBIx::Class::ResultSet" at ...

我错了什么？我试着把文件中的碎片联系在一起,但显然我弄错了.我从未见过一个关于多少关系应该如何工作的完整例子.

AFAIU,在Result类中定义关系应该在这个类中创建一个访问器.我怎么能看到所有经过处理的存取器？如果我尝试使用Data :: Printer转储ResultSet对象,我只看到列的访问器,但没有关系的访问器.

如果我尝试列表关系：

say $schema->source('Book')->relationships;

我在这里看不到many_to_many关系(也不是那些由DBIx :: Class :: Schema :: Loader拾取的关系),只有has_manys和belongs_tos.

编辑.添加最简单的测试用例：

创建表并填充数据

CREATE TABLE `book` (
  `bookID` int(10) unsigned NOT NULL AUTO_INCREMENT,`title` varchar(255) COLLATE utf8_estonian_ci NOT NULL DEFAULT '',PRIMARY KEY (`bookID`),KEY `title` (`title`)
) ENGINE=InnoDB;

CREATE TABLE `language` (
  `languageID` int(10) unsigned NOT NULL AUTO_INCREMENT,`language` varchar(255) COLLATE utf8_estonian_ci NOT NULL DEFAULT '',PRIMARY KEY (`languageID`),KEY `language` (`language`)
) ENGINE=InnoDB;

CREATE TABLE `book_language` (
  `book_languageID` int(10) unsigned NOT NULL AUTO_INCREMENT,`bookID` int(10) unsigned DEFAULT NULL,`languageID` int(10) unsigned DEFAULT NULL,PRIMARY KEY (`book_languageID`),UNIQUE KEY `book_language` (`bookID`,`languageID`),CONSTRAINT `book_language_ibfk_1` FOREIGN KEY (`languageID`) REFERENCES `language` (`languageID`) ON DELETE SET NULL,CONSTRAINT `book_language_ibfk_2` FOREIGN KEY (`bookID`) REFERENCES `book` (`bookID`) ON DELETE SET NULL
) ENGINE=InnoDB;

INSERT INTO language (language) VALUES ('estonian'),('english'),('polish');
INSERT INTO book (title) VALUES ('Eesti rahva ennemuistsed jutud'),('Estonska-polska slovar'),('21 facts about...'),('Englis-Polish Dictionary');
INSERT INTO book_language (bookID,languageID) VALUES (1,1),(2,3),(3,2),(4,3);

使用默认值生成架构：

dbicdump -o dump_directory=./lib -o debug=1 My::Schema 'dbi:mysql:dbname=testbook' user password

在Book.pm中添加了many_to_many-definitions

# Created by DBIx::Class::Schema::Loader v0.07046 @ 2017-03-21 18:49:05
# DO NOT MODIFY THIS OR ANYTHING ABOVE! md5sum:ipamXRkSe+HLXGdTGwzQ9w
__PACKAGE__->many_to_many('languages' => 'book_languages','languageid');

在Language.pm中

# Created by DBIx::Class::Schema::Loader v0.07046 @ 2017-03-21 18:49:05
# DO NOT MODIFY THIS OR ANYTHING ABOVE! md5sum:nZyaWdriRpgEWDAcO3+CFw
__PACKAGE__->many_to_many('books' => 'book_languages','bookid');

运行此脚本：

#!/usr/bin/env perl

use strict; use warnings; use 5.014; use utf8::all;
use My::Schema;

my $dsn = "DBI:mysql:database=testbook";
my $schema = My::Schema->connect( $dsn,'password' );

my $book_rs = $schema->resultset('Book');
say $book_rs->languages();