Typescript - How to create nested interface for json object

Question

I am trying to create nested json object for which I have created Interface.I am getting error as Type of property serservicesAndHeads are incompatible and says Property is missing. My Interface is as follows:

  interface  Head {
    HeadNumber?: string;
    HeadDescription?: string;
  };

  interface  ServicesAndHead {
    majorService?: string;
    subMajorService?: string;
    servicesAndHeads:Head[];
  }

  export interface MyTableItem {
   demandNo?: string;
   demandName?: string;
   servicesAndHeads?:ServicesAndHead;
   //servicesAndHeads?:ServicesAndHead[];
  }

Where my json looks like this:

  const dataItem: MyTableItem =
  {
    demandNo: 'Demand Number 2',
    demandName: 'Animal Husbandary, Livestock, Fisheries and Veterinary Services',
    servicesAndHeads: [
    {
      majorService: 'C-Economic Service',
      subMajorService: '(a) Agriculture and Allied Activities',
      majorHead: [
       { majorHeadNumber: '3098', majorHeadDescription: 'Animal Husbandry' },
       { majorHeadNumber: '3999', majorHeadDescription: 'Diary Development' },
       { majorHeadNumber: '4902', majorHeadDescription: 'Fisheries' }
      ]
    },
    {
      majorService: 'C- Capital Account of Economic Services',
      subMajorService: '(a) Capital Account of Agriculture and Allied Activities',
      majorHead: [
        { majorHeadNumber: '0012', majorHeadDescription: 'Capital Outlay on Animal ' },
        { majorHeadNumber: '3245', majorHeadDescription: 'Capital Outlay on Fisheries' }
      ]
     }
   ]
  }

I have tried this as well for nesting of serviceAndHead

  servicesAndHeads?: {
      [key: string]:ServicesAndHead,
      majorHeads?: {
        [key: string]:MajorHead
      };
  };

How would I rectify my code to accept the said json.

How are you typecasting your JSON into the interface object? I tried typecasting with <> but it didn't work for nested inteface. — Hokkyokusei
– Hokkyokusei, Commented Oct 29, 2021 at 9:45

Dilushika Weerawardhana · Accepted Answer · 2018-05-26 09:45:58Z

Define Interfaces as below:

interface  Head {
   majorHeadNumber?: string;
   majorHeadDescription?: string;
};

interface  ServicesAndHead {
   majorService?: string;
   subMajorService?: string;
   majorHead: Head[];
}

export interface MyTableItem {
   demandNo?: string;
   demandName?: string;
   servicesAndHeads?:ServicesAndHead[];
}

This will be compatible with your Json object.

const dataItem: MyTableItem = {

    demandNo: 'Demand Number 2',
    demandName: 'Animal Husbandary, Livestock, Fisheries and Veterinary Services',
    servicesAndHeads: [
    {
       majorService: 'C-Economic Service',
       subMajorService: '(a) Agriculture and Allied Activities',
       majorHead: [
       { 
          majorHeadNumber: '3098', 
          majorHeadDescription: 'Animal Husbandry' 
       },
       { 
          majorHeadNumber: '3999', 
          majorHeadDescription: 'Diary Development'
       },
       { 
          majorHeadNumber: '4902', 
          majorHeadDescription: 'Fisheries'
       }]
     },
     {
       majorService: 'C- Capital Account of Economic Services',
       subMajorService: '(a) Capital Account of Agriculture and Allied Activities',
       majorHead: [
       { 
          majorHeadNumber: '0012', 
          majorHeadDescription: 'Capital Outlay on Animal '
       },
       { 
          majorHeadNumber: '3245', 
          majorHeadDescription: 'Capital Outlay on Fisheries'
       }]
     }]
    }

Dmitry Egorov · Accepted Answer · 2018-05-26 09:34:53Z

0

The ServicesAndHead interface defines the servicesAndHeads property as mandatory but both dataItem.servicesAndHeads's array elements lack this property. They feature majorHead property instead. Perhaps, you meant

interface  ServicesAndHead {
  majorService?: string;
  subMajorService?: string;
  majorHead: Head[];
}

If so, you also need to adjust the Head interface as follows:

interface  Head {
  majorHeadNumber?: string;
  majorHeadDescription?: string;
};

answered May 26, 2018 at 9:34

Dmitry Egorov

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