预加载

预加载

当你从数据库检索数据时,也想同时获得与之相关联的查询,这被称为预加载.这个基本思路就是当你调用 find 或 findAll 时使用 include 属性.让我们假设以下设置:

class User extends Model {}
User.init({ name: Sequelize.STRING }, { sequelize, modelName: 'user' })
class Task extends Model {}
Task.init({ name: Sequelize.STRING }, { sequelize, modelName: 'task' })
class Tool extends Model {}
Tool.init({ name: Sequelize.STRING }, { sequelize, modelName: 'tool' })

Task.belongsTo(User)
User.hasMany(Task)
User.hasMany(Tool, { as: 'Instruments' })

sequelize.sync().then(() => {
  // 这是我们继续的地方 ...
})

首先,让我们用它们的关联 user 加载所有的 task.

Task.findAll({ include: [ User ] }).then(tasks => {
  console.log(JSON.stringify(tasks))

  /*
    [{
      "name": "A Task",
      "id": 1,
      "createdAt": "2013-03-20T20:31:40.000Z",
      "updatedAt": "2013-03-20T20:31:40.000Z",
      "userId": 1,
      "user": {
        "name": "John Doe",
        "id": 1,
        "createdAt": "2013-03-20T20:31:45.000Z",
        "updatedAt": "2013-03-20T20:31:45.000Z"
      }
    }]
  */
})

请注意,访问者(结果实例中的 User 属性)是单数形式,因为关联是一对一的.

接下来的事情:用多对一的关联加载数据！

User.findAll({ include: [ Task ] }).then(users => {
  console.log(JSON.stringify(users))

  /*
    [{
      "name": "John Doe",
      "id": 1,
      "createdAt": "2013-03-20T20:31:45.000Z",
      "updatedAt": "2013-03-20T20:31:45.000Z",
      "tasks": [{
        "name": "A Task",
        "id": 1,
        "createdAt": "2013-03-20T20:31:40.000Z",
        "updatedAt": "2013-03-20T20:31:40.000Z",
        "userId": 1
      }]
    }]
  */
})

请注意,访问者(结果实例中的 Tasks 属性)是复数形式,因为关联是多对一的.

如果关联是别名的(使用 as 参数),则在包含模型时必须指定此别名. 注意用户的 Tool 如何被别名为 Instruments. 为了获得正确的权限,你必须指定要加载的模型以及别名:

User.findAll({ include: [{ model: Tool, as: 'Instruments' }] }).then(users => {
  console.log(JSON.stringify(users))

  /*
    [{
      "name": "John Doe",
      "id": 1,
      "createdAt": "2013-03-20T20:31:45.000Z",
      "updatedAt": "2013-03-20T20:31:45.000Z",
      "Instruments": [{
        "name": "Toothpick",
        "id": 1,
        "createdAt": null,
        "updatedAt": null,
        "userId": 1
      }]
    }]
  */
})

你还可以通过指定与关联别名匹配的字符串来包含别名:

User.findAll({ include: ['Instruments'] }).then(users => {
  console.log(JSON.stringify(users))

  /*
    [{
      "name": "John Doe",
      "id": 1,
      "createdAt": "2013-03-20T20:31:45.000Z",
      "updatedAt": "2013-03-20T20:31:45.000Z",
      "Instruments": [{
        "name": "Toothpick",
        "id": 1,
        "createdAt": null,
        "updatedAt": null,
        "userId": 1
      }]
    }]
  */
})

User.findAll({ include: [{ association: 'Instruments' }] }).then(users => {
  console.log(JSON.stringify(users))

  /*
    [{
      "name": "John Doe",
      "id": 1,
      "createdAt": "2013-03-20T20:31:45.000Z",
      "updatedAt": "2013-03-20T20:31:45.000Z",
      "Instruments": [{
        "name": "Toothpick",
        "id": 1,
        "createdAt": null,
        "updatedAt": null,
        "userId": 1
      }]
    }]
  */
})

当预加载时,我们也可以使用 where 过滤关联的模型. 这将返回 Tool 模型中所有与 where 语句匹配的行的User.

User.findAll({
    include: [{
        model: Tool,
        as: 'Instruments',
        where: { name: { [Op.like]: '%ooth%' } }
    }]
}).then(users => {
    console.log(JSON.stringify(users))

    /*
      [{
        "name": "John Doe",
        "id": 1,
        "createdAt": "2013-03-20T20:31:45.000Z",
        "updatedAt": "2013-03-20T20:31:45.000Z",
        "Instruments": [{
          "name": "Toothpick",
          "id": 1,
          "createdAt": null,
          "updatedAt": null,
          "userId": 1
        }]
      }],

      [{
        "name": "John Smith",
        "id": 2,
        "createdAt": "2013-03-20T20:31:45.000Z",
        "updatedAt": "2013-03-20T20:31:45.000Z",
        "Instruments": [{
          "name": "Toothpick",
          "id": 1,
          "createdAt": null,
          "updatedAt": null,
          "userId": 1
        }]
      }],
    */
  })

当使用 include.where 过滤一个预加载的模型时,include.required 被隐式设置为 true. 这意味着内部联接完成返回具有任何匹配子项的父模型.

使用预加载模型的顶层 WHERE

将模型的 WHERE 条件从 ON 条件的 include 模式移动到顶层,你可以使用 '$nested.column$' 语法:

User.findAll({
    where: {
        '$Instruments.name$': { [Op.iLike]: '%ooth%' }
    },
    include: [{
        model: Tool,
        as: 'Instruments'
    }]
}).then(users => {
    console.log(JSON.stringify(users));

    /*
      [{
        "name": "John Doe",
        "id": 1,
        "createdAt": "2013-03-20T20:31:45.000Z",
        "updatedAt": "2013-03-20T20:31:45.000Z",
        "Instruments": [{
          "name": "Toothpick",
          "id": 1,
          "createdAt": null,
          "updatedAt": null,
          "userId": 1
        }]
      }],

      [{
        "name": "John Smith",
        "id": 2,
        "createdAt": "2013-03-20T20:31:45.000Z",
        "updatedAt": "2013-03-20T20:31:45.000Z",
        "Instruments": [{
          "name": "Toothpick",
          "id": 1,
          "createdAt": null,
          "updatedAt": null,
          "userId": 1
        }]
      }],
    */

包括所有

要包含所有属性,你可以使用 all:true 传递单个对象:

User.findAll({ include: [{ all: true }]});

包括软删除的记录

如果想要加载软删除的记录,可以通过将 include.paranoid 设置为 false 来实现

User.findAll({
    include: [{
        model: Tool,
        where: { name: { [Op.like]: '%ooth%' } },
        paranoid: false // query and loads the soft deleted records
    }]
});

排序预加载关联

在一对多关系的情况下.

Company.findAll({ include: [ Division ], order: [ [ Division, 'name' ] ] });
Company.findAll({ include: [ Division ], order: [ [ Division, 'name', 'DESC' ] ] });
Company.findAll({
  include: [ { model: Division, as: 'Div' } ],
  order: [ [ { model: Division, as: 'Div' }, 'name' ] ]
});
Company.findAll({
  include: [ { model: Division, as: 'Div' } ],
  order: [ [ { model: Division, as: 'Div' }, 'name', 'DESC' ] ]
});
Company.findAll({
  include: [ { model: Division, include: [ Department ] } ],
  order: [ [ Division, Department, 'name' ] ]
});

在多对多关系的情况下,你还可以通过表中的属性进行排序.

Company.findAll({
  include: [ { model: Division, include: [ Department ] } ],
  order: [ [ Division, DepartmentDivision, 'name' ] ]
});

嵌套预加载

你可以使用嵌套的预加载来加载相关模型的所有相关模型:

User.findAll({
  include: [
    {model: Tool, as: 'Instruments', include: [
      {model: Teacher, include: [ /* etc */]}
    ]}
  ]
}).then(users => {
  console.log(JSON.stringify(users))

  /*
    [{
      "name": "John Doe",
      "id": 1,
      "createdAt": "2013-03-20T20:31:45.000Z",
      "updatedAt": "2013-03-20T20:31:45.000Z",
      "Instruments": [{ // 1:M and N:M association
        "name": "Toothpick",
        "id": 1,
        "createdAt": null,
        "updatedAt": null,
        "userId": 1,
        "Teacher": { // 1:1 association
          "name": "Jimi Hendrix"
        }
      }]
    }]
  */
})

这将产生一个外连接. 但是,相关模型上的 where 语句将创建一个内部连接,并仅返回具有匹配子模型的实例. 要返回所有父实例,你应该添加 required: false.

User.findAll({
  include: [{
    model: Tool,
    as: 'Instruments',
    include: [{
      model: Teacher,
      where: {
        school: "Woodstock Music School"
      },
      required: false
    }]
  }]
}).then(users => {
  /* ... */
})

以上查询将返回所有用户及其所有乐器,但只会返回与 Woodstock Music School 相关的老师.

包括所有也支持嵌套加载:

User.findAll({ include: [{ all: true, nested: true }]});

使用 right join 进行关联

默认情况下, 关联是使用 left join 加载的, 也就是说, 它仅包括来自父表的记录. 如果您使用的方言支持，可以通过传递 right 属性来将这种行为更改为右连接. 目前, sqlite 不 支持right joins.

注意: 仅当 required 是 false 时才遵循 right.

User.findAll({
    include: [{
        model: Tool // 将创建 left join
    }]
});

User.findAll({
    include: [{
        model: Tool,
        right: true // 将创建 right join
    }]
});

User.findAll({
    include: [{
        model: Tool,
        required: true,
        right: true // 没有作用, 将创建一个 inner join
    }]
});

User.findAll({
    include: [{
        model: Tool,
        where: { name: { [Op.like]: '%ooth%' } },
        right: true // 没有作用, 将创建一个 inner join
    }]
});

User.findAll({
    include: [{
        model: Tool,
        where: { name: { [Op.like]: '%ooth%' } },
        required: false
        right: true // 因为我们设置 `required` 为 false, 这将创建一个 right join
    }]
});