Sequelize：查找没有关联的条目

给出以下简单模型：

class A extends Model {}
A.init({
    aField: DataTypes.STRING,
}, { sequelize });

class B extends Model {}
B.init({
    bField: DataTypes.STRING,
}, { sequelize });

A.hasMany(B); // this creates the B.AId column


// populate

await A.create({
    aField: 'fooA',
    Bs: [{ bField: 'fooB' }]
}, { include: [B] });

await A.create({ aField: 'barA' });
await A.create({ aField: 'bazA' });

我不知道如何选择第一个没有 B 条目的 A 模型实例。
前一种情况，返回即可barA and bazA.

以下不起作用，它返回foo:

await A.findOne({
    include: [{
        model: B,
        required: false,
        where: {
            'AId': null,
        }
    }],
});

生成的查询是：SELECT A.*, Bs.id AS Bs.id, Bs.bField AS Bs.bField, Bs.AId AS Bs.AId FROM (SELECT A.id, A.aField FROM As AS A LIMIT 1) AS A LEFT OUTER JOIN Bs AS Bs ON A.id = Bs.AId AND Bs.AId IS NULL

这是一个极限和关联的问题。类似问题：https://github.com/sequelize/sequelize/issues/7585 https://github.com/sequelize/sequelize/issues/7585

Sequelize 将关联转变为子查询，但在您的用例中，您需要一个关联，然后限制总体关联结果。 为此，您可以使用subQuery: false禁用子查询。

await A.findOne({
    include: [{
        model: B,
        required: false,
        where: {
            'AId': null,
        }
    }],
    subQuery: false
});

这仍然无法实现你想要的，因为where in include将生成AND的条件ON.

生成的查询：

SELECT `A`.`id`, `A`.`aField`, `A`.`createdAt`, `A`.`updatedAt`, `Bs`.`id` AS `Bs.id`, 
    `Bs`.`bField` AS `Bs.bField`, `Bs`.`createdAt` AS `Bs.createdAt`, 
    `Bs`.`updatedAt` AS `Bs.updatedAt`, `Bs`.`AId` AS `Bs.AId` 
FROM `As` AS `A` 
LEFT OUTER JOIN `Bs` AS `Bs` ON `A`.`id` = `Bs`.`AId` AND `Bs`.`AId` IS NULL 
LIMIT 1;

你想要的是

...
... ON `A`.`id` = `Bs`.`AId` WHERE `Bs`.`AId` IS NULL 
LIMIT 1;

为了得到这个WHERE，你可以把where条款为A.

await A.findOne({
    include: [{
        model: B,
        required: false
    }],
    where: {
        '$Bs.AId$': null
    },
    subQuery: false
});