Material UI datagrid with nested data

To solve the problem, let's see params object passed in valueGetter function. Log that and you will find a row object under it. Instead of using params.getValue(), you should access the row object. It seems that params.getValue() can only be used on one-level JSON object. Here is the code snippet to output phone field.

  {
    field: "phone",
    headerName: "Phone",
    width: 160,
    valueGetter: (params) => {
      console.log({ params });
      let result = [];
      if (params.row.phone) {
        if (params.row.phone.home) {
          result.push("home: " + params.row.phone.home);
        }
        if (params.row.phone.office) {
          result.push("office: " + params.row.phone.office);
        }
      } else {
        result = ["Unknown"];
      }
      return result.join(", ");
    }
  }

Update

To have more flexibility on checking if every key under a object exists, I have created a helper method:

const checkKeysUnderObject = (obj, result) => {
  for (let key in obj) {
    if (key) { // push the value to the result array only if key exists
      result.push(key + ": " + obj[key]);
    }
  }
};

usage of the helper method:

if (params.row.phone) {
  checkKeysUnderObject(params.row.phone, result);
}else{
  result = ["Unknown"];
}

I have also updated the codesandbox here.

I use this in my project :

{ 
    field: 'idMaintenancePlan',
    headerName: 'Plan de maintenance', 
    sortable: false, width: 200, 
    valueFormatter: (params) => params.row?.maintenancePlan?.name 
}

this works fine also

{
     field: "family",
     headerName: "Family",
     width: 150,
     renderCell: (params) => {
       return <div className="rowitem">{params.row.family.name}</div>;
     },
},

this works fine for me

{ field: 'parserInfo', headerName: 'Parser Title', valueFormatter: ({ value }) => value.title }