如何在Javascript中映射数组一对多关系答案

【问题标题】：How to map array one to many relationship in Javascript如何在Javascript中映射数组一对多关系
【发布时间】：2020-07-24 08:01:55
【问题描述】：

我正在尝试使用 map 函数将以下 JSON 数据转换为适当的输出

[{"jobId":100049,"name":"Drilling","jobNumber":"1222455","address":"Ahmedabad","city":"Ahmedabad","state":"1","zip":"38003","active":true,"jobOwnerId":100002,"jobOwnerName":"Troy Thomson","createdBy":"","createdOn":"2020-03-15T18:42:25.6533333","modifiedBy":"","modifiedOn":"2020-03-16T13:21:53.0333333","members":[{"memberId":100001,"memberName":"Hardik Gondalia"},{"memberId":100004,"memberName":"Micheal T. Angelo"}],"assets":[{"assetId":100004,"assetName":"Minima ullam non mol"}]},{"jobId":100051,"name":"Drilling The Hole","jobNumber":"11111","address":"201, AA 333 Steet, Time Square","city":"Boston","state":"1","zip":"11111","active":true,"jobOwnerId":100001,"jobOwnerName":"Hardik Gondalia","createdBy":"","createdOn":"2020-03-25T11:12:13.89","modifiedBy":"","modifiedOn":"2020-03-25T11:12:32.1266667","members":[{"memberId":100002,"memberName":"Troy Thomson"}],"assets":[{"assetId":100005,"assetName":"Drill Machine P2222"}]}]

期望的输出：

[{"jobid":100049,"memberid":100001],{"jobid":100049,"memberid":100004],{"jobid":100051,"memberid":100002]}

如您所见，job 是 json 对象，其中包含成员和资产数组。如果它有多个成员或资产，我想重复 jobid。

我试过的是：

const assignmentAssetModel = this.jobList.map(i => ({ jobid: i.jobId, assetid: i.assets.map(j => j.assetId) }));

但它给了我以下输出：

[{"jobid":100049,"memberid":[100001,100004]},{"jobid":100051,"memberid":[100002]}]

如果你有多个 memberid，我想重复 jobid

【问题讨论】：

标签： javascript ecmascript-6 array.prototype.map

【解决方案1】：

您可以使用Array#flatMap 并映射外部和内部属性。

var data = [{ jobId: 100049, name: "Drilling", jobNumber: "1222455", address: "Ahmedabad", city: "Ahmedabad", state: "1", zip: "38003", active: true, jobOwnerId: 100002, jobOwnerName: "Troy Thomson", createdBy: "", createdOn: "2020-03-15T18:42:25.6533333", modifiedBy: "", modifiedOn: "2020-03-16T13:21:53.0333333", members: [{ memberId: 100001, memberName: "Hardik Gondalia" }, { memberId: 100004, memberName: "Micheal T. Angelo" }], assets: [{ assetId: 100004, assetName: "Minima ullam non mol" }] }, { jobId: 100051, name: "Drilling The Hole", jobNumber: "11111", address: "201, AA 333 Steet, Time Square", city: "Boston", state: "1", zip: "11111", active: true, jobOwnerId: 100001, jobOwnerName: "Hardik Gondalia", createdBy: "", createdOn: "2020-03-25T11:12:13.89", modifiedBy: "", modifiedOn: "2020-03-25T11:12:32.1266667", members: [{ memberId: 100002, memberName: "Troy Thomson" }], assets: [{ assetId: 100005, assetName: "Drill Machine P2222" }] }],
    result = data.flatMap(({ jobId, members }) =>
        members.map(({ memberId }) => ({ jobId, memberId })));

console.log(result);

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【讨论】：

【解决方案2】：

您可以使用Array.reduce() 代替Array.map()，因为结果数组的长度与初始数组的长度不同。

const jobList = [{"jobId":100049,"name":"Drilling","jobNumber":"1222455","address":"Ahmedabad","city":"Ahmedabad","state":"1","zip":"38003","active":true,"jobOwnerId":100002,"jobOwnerName":"Troy Thomson","createdBy":"","createdOn":"2020-03-15T18:42:25.6533333","modifiedBy":"","modifiedOn":"2020-03-16T13:21:53.0333333","members":[{"memberId":100001,"memberName":"Hardik Gondalia"},{"memberId":100004,"memberName":"Micheal T. Angelo"}],"assets":[{"assetId":100004,"assetName":"Minima ullam non mol"}]},{"jobId":100051,"name":"Drilling The Hole","jobNumber":"11111","address":"201, AA 333 Steet, Time Square","city":"Boston","state":"1","zip":"11111","active":true,"jobOwnerId":100001,"jobOwnerName":"Hardik Gondalia","createdBy":"","createdOn":"2020-03-25T11:12:13.89","modifiedBy":"","modifiedOn":"2020-03-25T11:12:32.1266667","members":[{"memberId":100002,"memberName":"Troy Thomson"}],"assets":[{"assetId":100005,"assetName":"Drill Machine P2222"}]}]


const jobsPerMember = jobList.reduce((acc, cur) => {
  cur.members.forEach((member) => acc.push({
      jobid: cur.jobId,
      memberid: member.memberId
  }))
  return acc
},[])

console.log(jobsPerMember)

【讨论】：

【解决方案3】：

您应该改用.reduce 方法：

this.jobList.reduce((acc, { members, jobId }) => {
   return [...acc, ...members.map(({ memberId }) => ({ jobId, memberId }))]; 
}, []);

如果您的目标是更新版本的 javascript (ES2019)，您也可以使用 flatMap：

this.jobList.flatMap(({ members, jobId }) => members.map(({ memberId }) => ({ jobId, memberId })));

【讨论】：