Question

我正在尝试将来自MySql right join的行数组转换为nodeJS上的array/json格式。考虑通用的mysql表：

emp_id  name
1       john
2       bill
3       anna


fk_emp_id   project
1           p1
1           p2
1           p3
2           p1
2           p4

他们正确加入：

id  name fk_emp_id  project
1   john    1       p1
1   john    1       p2
1   john    1       p3
2   bill    2       p1
2   bill    2       p4
3   anna    3       null

这是：

rows = [
    {"id":1, "name":"john", "fk_emp_id" : "1" , "project" : "p1"},
    {"id":1, "name":"john", "fk_emp_id" : "1" , "project" : "p2"},
    {"id":1, "name":"john", "fk_emp_id" : "1" , "project" : "p3"},
    {"id":2, "name":"bill", "fk_emp_id" : "2" , "project" : "p1"},
    {"id":2, "name":"bill", "fk_emp_id" : "2" , "project" : "p4"},
    {"id":3, "name":"anna", "fk_emp_id" : "3" , "project" : null}
]

如何将它们转换为此JSON：

result = [
    {id: '1',
     name: 'john',
     projects: [p1, p2, p3]
    }
    ,
    {id: '2',
     name: 'bill',
     projects: [p1, p4]
    }
    ,
    {id: '3',
     name: 'anna',
     projects: []
    }
]

Answer 1

如果您只查看将result转换为id数组的版本，则可以使用Map作为哈希表，以获取给定var rows = [{ id: 1, name: "john", fk_emp_id: "1", project: "p1" }, { id: 1, name: "john", fk_emp_id: "1", project: "p2" }, { id: 1, name: "john", fk_emp_id: "1", project: "p3" }, { id: 2, name: "bill", fk_emp_id: "2", project: "p1" }, { id: 2, name: "bill", fk_emp_id: "2", project: "p4" }, { id: 3, name: "anna", fk_emp_id: "3", project: null }], result = []; rows.forEach(function (a) { var reference = this.get(a.id); if (!reference) { reference = { id: a.id, name: a.name, fk_emp_id: a.fk_emp_id, projects: [] }; this.set(a.id, reference); result.push(reference); } a.project && reference.projects.push(a.project); }, new Map); console.log(result);的引用

.as-console-wrapper { max-height: 100% !important; top: 0; }

class Post < ActiveRecord::Base
  has_many :taggings
  has_many :tags, through: :taggings
  has_many :collectables
  has_many :collections, through: :collectables
end

SQL右连接到JSON /数组

1 个答案: