sql - 如何编写可能来自不同表的 "belongs to"关联？

Question

如何为属于模型 B 或模型 C 但不属于两者的模型 A 编写关联？

假设我有一个员工模型、承包商模型和一个事件模型。关联如下:
员工有很多事件。
承包商有许多事件。
事件属于承包商或员工。

我是否创建了一个连接表employee_contractor 并说事件属于employee_contractor？

这可能非常简单，但是对于 Sequelize/DB 编程来说非常陌生，我很难理解何时使用以及使用什么。我知道可能有这类问题的答案，但我不知道用什么语言来正确地表达我的问题以找到它们。

// Employee model
'use strict';
module.exports = (sequelize, DataTypes) => {
  const Employee = sequelize.define('Employee', {
    firstName: DataTypes.STRING,
    lastName: DataTypes.STRING,
    // other fields
    //...

  }, {});
  Employee.associate = function(models) {
    // associations can be defined here
  };
  return Employee;
};

// Contractor model
'use strict';
module.exports = (sequelize, DataTypes) => {
  const Contractor = sequelize.define('Contractor', {
    firstName: DataTypes.STRING,
    lastName: DataTypes.STRING,
    company: DataTypes.STRING,
    // other fields
    //...

  }, {});
  Contractor.associate = function(models) {
    // associations can be defined here
  };
  return Contractor;
};

// Event Model
'use strict';
module.exports = (sequelize, DataTypes) => {
  const Event = sequelize.define('Event', {
    reason: DataTypes.STRING,
    escort: DataTypes.STRING,
    // other fields
    //...

  }, {});
  Event.associate = function(models) {
    // associations can be defined here
  };
  return Event;
};

Answer 1

在这种情况下，我建议将事件拆分为两个不同的事件:employeeEvents 和 ContractorEvents(以便在以后查询操作时更容易地利用 Sequelize 关联)，并在每种类型的事件上使用简单的 belongsTo，对 Actor 使用 hasMany。
Employee

// Employee model
'use strict';
module.exports = (sequelize, DataTypes) => {
  const Employee = sequelize.define('Employee', {
    firstName: DataTypes.STRING,
    lastName: DataTypes.STRING,
    // other fields
    //...

  }, {});
  Employee.associate = function(models) {
    // associations can be defined here
    Employee.hasMany(models.EmployeeEvent);
  };
  return Employee;
};

EmployeeEvents

// EmployeeEvent Model
'use strict';
module.exports = (sequelize, DataTypes) => {
  const EmployeeEvent = sequelize.define('Event', {
    reason: DataTypes.STRING,
    escort: DataTypes.STRING,
    // other fields
    //...

  }, {});
  EmployeeEvent.associate = function(models) {
    // associations can be defined here
    EmployeeEvent.belongsTo(models.Employee);
  };
  return EmployeeEvent;
};

Contractor

// Contractor model
'use strict';
module.exports = (sequelize, DataTypes) => {
  const Contractor = sequelize.define('Contractor', {
    firstName: DataTypes.STRING,
    lastName: DataTypes.STRING,
    company: DataTypes.STRING,
    // other fields
    //...

  }, {});
  Contractor.associate = function(models) {
    // associations can be defined here
    Contractor.hasMany(models.ContractorEvent);
  };
  return Contractor;
};

ContractorEvents

// ContractorEvent Model
'use strict';
module.exports = (sequelize, DataTypes) => {
  const ContractorEvent = sequelize.define('Event', {
    reason: DataTypes.STRING,
    escort: DataTypes.STRING,
    // other fields
    //...

  }, {});
  ContractorEvent.associate = function(models) {
    // associations can be defined here
    ContractorEvent.belongsTo(models.Employee);
  };
  return ContractorEvent;
};