为什么sequelize会在一个模型中创建两个foreign_keys的同时自动创建一个key？

Question

我创建了三个表:designer，tag，designer_tag.designer_tag是一个带有两个外键的表，它们是designer的id和tag的id。

表[设计器]:

module.exports = (sequelize, DataTypes) => {
    let Designer = sequelize.define('Designer', {
        id: {
            allowNull: false,
            autoIncrement: true,
            comment: 'ID',
            primaryKey: true,
            type: DataTypes.INTEGER(11).UNSIGNED
        },
        name: {
            allowNull: false,
            comment: 'name',
            defaultValue: '',
            type: DataTypes.STRING(10)
        },
        begin_time: {
            allowNull: false,
            comment: 'begin_time',
            defaultValue: 0,
            type: DataTypes.INTEGER(10).UNSIGNED
        },
        avatar: {
            allowNull: false,
            comment: 'avatar',
            defaultValue: '',
            type: DataTypes.STRING(120)
        },
        description: {
            allowNull: false,
            comment: 'description',
            defaultValue: '',
            type: DataTypes.STRING(120)
        },
        create_time: {
            allowNull: false,
            comment: 'create time',
            defaultValue: 0,
            type: DataTypes.INTEGER(10).UNSIGNED
        }
    }, {
        comment: 'designer',
        freezeTableName: true,
        tableName: 'designer',
        timestamps: false,
        underscored: true
    });
    Designer.associate = models => {
        Designer.hasOne(models.DesignerTag);
    };
    return Designer;
};

表[标记]:

module.exports = (sequelize, DataTypes) => {
    let Tag = sequelize.define('Tag', {
        id: {
            allowNull: false,
            autoIncrement: true,
            comment: 'ID',
            primaryKey: true,
            type: DataTypes.INTEGER(11).UNSIGNED
        },
        name: {
            allowNull: false,
            comment: 'name',
            defaultValue: '',
            type: DataTypes.STRING(20)
        },
        create_time: {
            allowNull: false,
            comment: 'create time',
            defaultValue: 0,
            type: DataTypes.INTEGER(10).UNSIGNED
        }
    }, {
        comment: 'tag',
        freezeTableName: true,
        indexes: [{
            name: 'name',
            method: 'BTREE',
            fields: ['name'],
            unique: true
        }],
        tableName: 'tag',
        timestamps: false,
        underscored: true
    });
    Tag.associate = models => {
        Tag.hasOne(models.DesignerTag);
    };
    return Tag;
};

表[designer_tag]:

module.exports = (sequelize, DataTypes) => {
    let DesignerTag = sequelize.define('DesignerTag', {
        id: {
            allowNull: false,
            autoIncrement: true,
            comment: 'ID',
            primaryKey: true,
            type: DataTypes.INTEGER(11).UNSIGNED
        },
        create_time: {
            allowNull: false,
            comment: 'create time',
            defaultValue: 0,
            type: DataTypes.INTEGER(10).UNSIGNED
        }
    }, {
        comment: 'designer tag table',
        freezeTableName: true,
        indexes: [{
            name: 'designer_tag_unique',
            method: 'BTREE',
            fields: ['designer_id', 'tag_id'],
            unique: true
        }],
        tableName: 'designer_tag',
        timestamps: false,
        underscored: true
    });
    DesignerTag.associate = models => {
        DesignerTag.belongsTo(models.Tag);
        DesignerTag.belongsTo(models.Designer);
    };
    return DesignerTag;
};

最后，表[designer_tag]如下所示:

CREATE TABLE `designer_tag` (
  `id` int unsigned NOT NULL AUTO_INCREMENT COMMENT 'ID',
  `create_time` int unsigned NOT NULL DEFAULT '0' COMMENT 'create_time',
  `designer_id` int unsigned DEFAULT NULL,
  `tag_id` int unsigned DEFAULT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `designer_tag_unique` (`designer_id`,`tag_id`),
  KEY `tag_id` (`tag_id`),
  CONSTRAINT `designer_tag_ibfk_3` FOREIGN KEY (`designer_id`) REFERENCES `designer` (`id`) ON DELETE SET NULL ON UPDATE CASCADE,
  CONSTRAINT `designer_tag_ibfk_4` FOREIGN KEY (`tag_id`) REFERENCES `tag` (`id`) ON DELETE SET NULL ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci COMMENT='designer tag';

自动创建的密钥(tag_id)是不是很奇怪？ Sequeize版本是5.21.10。 请有同样情况的人说说为什么会这样。 谢谢。

Answer 1

难道这个代码不是自动创建外部字段tag_id吗？？

 DesignerTag.associate = models => {
        DesignerTag.belongsTo(models.Tag);
        DesignerTag.belongsTo(models.Designer);
    };

所以逻辑上标记表和设计器表有多对多的关系。