我正在尝试理解 Sequelize 中的关联。我从现有的数据库表开始，因此某些字段可能与 Sequelize 中的默认值不匹配。我使用 Sequelizer 直接从数据库生成我的模型。 我习惯于编写查询，但现在我正在尝试学习像 Sequelize 这样的 ORM 是如何工作的。

这是我的模型。

models/user.js

module.exports = (sequelize, DataTypes) => {
  const User = sequelize.define(
    "User",
    {
      id: {
        type: DataTypes.INTEGER(11),
        allowNull: false,
        primaryKey: true,
        field: "id"
      },
      username: {
        type: DataTypes.STRING(20),
        allowNull: false,
        field: "username"
      },
      fullname: {
        type: DataTypes.STRING(60),
        allowNull: false,
        field: "fullname"
      },
      createdat: {
        type: DataTypes.DATE,
        allowNull: false,
        field: "createdat"
      },
      updateat: {
        type: DataTypes.DATE,
        allowNull: true,
        field: "updateat"
      },
      deletedat: {
        type: DataTypes.DATE,
        allowNull: true,
        field: "deletedat"
      }
    },
    {
      tableName: "users",
      timestamps: false
    }
  );

  User.associate = function(models) {
        models.User.hasMany(models.Ticket),
        { as: "createdbyname", foreignKey: "createdby" };
  };
  return User;
};

models/ticket.js

module.exports = (sequelize, DataTypes) => {
  const Ticket = sequelize.define(
    "Ticket",
    {
      id: {
        type: DataTypes.INTEGER(11),
        allowNull: false,
        primaryKey: true,
        field: "id"
      },
      details: {
        type: DataTypes.STRING(45),
        allowNull: true,
        field: "details"
      },
      assignedto: {
        type: DataTypes.INTEGER(11),
        allowNull: true,
        field: "assignedto"
      },
      createdby: {
        type: DataTypes.INTEGER(11),
        allowNull: true,
        field: "createdby"
      },
      createdat: {
        type: DataTypes.DATE,
        allowNull: false,
        field: "createdat"
      },
      updatedat: {
        type: DataTypes.DATE,
        allowNull: true,
        field: "updatedat"
      },
      deletedat: {
        type: DataTypes.DATE,
        allowNull: true,
        field: "deletedat"
      }
    },
    {
      tableName: "tickets",
      timestamps: false
    }
  );

  Ticket.associate = function(models) {
        models.Ticket.belongsTo(models.User,
            { foreignKey: "createdby" });
  };
  return Ticket;
};

在我的路由处理程序中，我按如下方式调用 User.findAll:

  models.User.findAll({
    include: [models.Ticket]
  })

我希望看到的结果是一个如下所示的查询:

SELECT 
    `User`.`id`,
    `User`.`username`,
    `User`.`fullname`,
    `User`.`createdat`,
    `User`.`updateat`,
    `User`.`deletedat`,
    `Tickets`.`id` AS `Tickets.id`,
    `Tickets`.`details` AS `Tickets.details`,
    `Tickets`.`assignedto` AS `Tickets.assignedto`,
    `Tickets`.`createdby` AS `Tickets.createdby`,
    `Tickets`.`createdat` AS `Tickets.createdat`,
    `Tickets`.`updatedat` AS `Tickets.updatedat`,
    `Tickets`.`deletedat` AS `Tickets.deletedat`
FROM
    `users` AS `User`
LEFT OUTER JOIN
    `tickets` AS `Tickets` ON `User`.`id` = `Tickets`.`createdby`

我在控制台中看到的查询是:

SELECT 
    `User`.`id`,
    `User`.`username`,
    `User`.`fullname`,
    `User`.`createdat`,
    `User`.`updateat`,
    `User`.`deletedat`,
    `Tickets`.`id` AS `Tickets.id`,
    `Tickets`.`details` AS `Tickets.details`,
    `Tickets`.`assignedto` AS `Tickets.assignedto`,
    `Tickets`.`createdby` AS `Tickets.createdby`,
    `Tickets`.`createdat` AS `Tickets.createdat`,
    `Tickets`.`updatedat` AS `Tickets.updatedat`,
    `Tickets`.`deletedat` AS `Tickets.deletedat`,
    `Tickets`.`UserId` AS `Tickets.UserId`
FROM
    `users` AS `User`
LEFT OUTER JOIN
    `tickets` AS `Tickets` ON `User`.`id` = `Tickets`.`UserId`;

注意 LEFT OUTER JOIN 子句的区别。这是抛出如下错误:

Unhandled rejection SequelizeDatabaseError: Unknown column 'Tickets.UserId' in 'field list'

我需要一些帮助来弄清楚我哪里出了问题。

最佳答案

定义关联时，例如 belongsTo，您可以指定一个 foreignKey 和一个 targetKey。 foreignKey 对应于源表中的字段(记住，语法是 sourceModel.belongsTo(targetModel, options))。 targetKey对应目标表中的字段。

在你的例子中，你在 models/ticket.js 文件中的关联中犯了一个错误，你使用了:

models.Ticket.belongsTo(models.User, { foreignKey: "createdby" });

此处，foreignKey 引用源表 Ticket。因此，您告诉 Sequelize 为 Ticket 表使用字段 createdBy，为 User 表使用默认值(主键)。由于 createdBy 不存在于 Ticket 中，Sequelize 回退到默认情况，它使用 Ticket.UserID。

要修复关联(和查询)，您需要将 belongsTo 更新为以下内容:

models.Ticket.belongsTo(models.User, { targetKey: "createdby" });

关于mysql - 了解 Sequelize 中的关联，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/56122602/