如何在我的模型中通过多对多关系表改进搜索？

Question

Just for simplify my problem, let's say i have a project for a library system that implements all features for borrow, count, search, and add books in my library.

For that project i made 3 main tables: person (id, name, etc) , loan (id, id_person, dates, etc) and, of course, book (id, title, etc) .

Since a Person can borrow more than one book at same time, i also needed another table just to link this many-to-many relationship. rel_loan_book (id, id_book, id_loan) .

Now, in my Book View i have a Gridview with all information of the book and a column saying whether the book is available for borrow or not (not being used at the moment).

Here is what i'm doing at the moment:

View:

[
    'attribute' => 'isAvaliable',
    'value' => function($model) {
        return $model->currentLoan ? 'No' :'Yes';
    },
    'filter' => Html::activeDropDownList($searchModel, 'isAvaliable', ['1' => 'Yes', '0' => 'No'],
        ['class'=>'form-control','prompt' => '']
    )
],

Model Book:

public function getCurrentLoan()
{
     return $this->hasOne(Loan::className(), ['id' => 'id_loan'])
         ->viaTable(RelLoanBook::tableName(), ['id_book' => 'id'])
         ->onCondition(['loan.status' => 'A']);
}

Status 'A' in Loan table means it's still active (the book didn't came back).

My problem is when i try to make a search by available or not available books... At the moment, i'm doing another query just to check what are the borrowed books and then removing (or filtering by) this ids in my search:

BookSearch:

public $isAvaliable;

...

public function rules()
{
    return [
        [['isAvaliable'], 'safe'],
    ];
}

...

public function search($params)
{
    ...

    if ($this->isAvaliable !== '') {
        $subQuery = Book::find()->select('book.id');
        $subQuery->joinWith(['currentLoan'])
            ->andWhere(['is not' , 'loan.id', null])
            ->all();

        if ($this->isAvaliable === '1') {
            $query->andWhere(['not in', 'book.id', $subQuery]);
        } elseif ($this->isAvaliable === '0') {
            $query->andWhere(['in', 'book.id', $subQuery]);
        }
    }

    ...
}

I don't think this is the best approach for that. But i can't think in a sql query making that search without a subquery:

SELECT * FROM book
LEFT JOIN rel_loan_book ON rel_loan_book.book_id = book.id
LEFT JOIN loan ON loan.id = rel_loan_book.loan.id
WHERE ( /* my filters */)
AND ( /* some restriction that check if the book does OR does not have a loan with status === 'A' */)

Answer 1

First off, do you have a reason for not making loan the junction table? This seems more logical to me and would simplify your query.

Ie:

• person(id, name)
• book(id, name, author, isbn, publisher, genre, tags)
• loan(id, person_id, book_id, start_date, due_date, return_date, status)

By connecting book and loan the system is more flexible, allowing for:

• loan extensions on some of the titles picked up
• early returns for some of the items

It would be weird if a library would refuse the return of all books if you forgot one of them. That only happens when they are all connected to a single loan.

After a little structural revision, add this to book model:

public function getIsAvailable()
{
    return !Loan::find()->where([
        'book_id' => $this->id,
        'status' => 'A'
    ])->exists();
}

If a loan record with an active status and this book id exists, then its not available.

Add isAvailable attribute to the search filter:

 $query->andFilterWhere([
     ...
     'isAvailable' => $this->isAvailable,
 ]);

Links the getIsAvailable function with the dropdown filter.

Adjust isAvailable column in book-view:

[
    'attribute' => 'isAvailable',
    'value' => function($model) {
        return $model->isAvailable ? 'Yes' :'No';
    },
    'filter' => Html::activeDropDownList($searchModel, 'isAvailable', 
        [0 => 'No', 1 => 'Yes'],
        ['class'=>'form-control','prompt' => '']
    )
],