How to set array index of normalized data

问题

I am trying to normalize a dataset, update an array index, and then denormalize the data.

I'd like to change a P.O. at on a header line and have the change propagate to a linked order.

The data model is as follows:

let numSet = 0;
let numLine = 2;

let data = [
  {
    "order": {
      "po_no": "original-po"
    },
    "items": [
      {
        "header": {
          "po_no": "keep-this-value",
          "set_no": 0
        },
        "line": {
          "id": "A123",
          "line_no": 1
        }
      },
      {
        "header": {
          "po_no": "update-with-this-value",
          "set_no": 0
        },
        "line": {
          "id": "B234",
          "line_no": 2
        }
      }
    ]
  }
];

// The logic to normalize the data (appending the order data to each index), works as expected

let normalizedDataSet = [];
for (let i = 0; i < data.length; i++) {
  for (let j = 0; j < data[i]['items'].length; j++) {
    data[i]['items'][j]['order'] = data[i]['order']; // Set default header
    normalizedDataSet.push(data[i]['items'][j]);
  }
}

// The logic to update the normalized data, updating too many indices

for (i = 0; i < normalizedDataSet.length; i++) {
  let index = normalizedDataSet[i];

  if (numSet === index['header']['set_no'] && numLine === index['line']['line_no']) {
    index['order']['po_no'] = index['header']['po_no'];
  }
}

console.log(normalizedDataSet); // Expected output below

Expected output:

normalizedDataSet = [
  { 
    "header": { 
      "po_no": 'keep-this-value', 
      "set_no": 0 
    },
    "line": { 
      "id": 'A123', 
      "line_no": 1 
    },
    "order": { 
      "po_no": 'original-po' 
    } 
  },
  { 
    "header": { 
      "po_no": 'update-with-this-value', 
      "set_no": 0 
    },
    "line": { 
      "id": 'B234', 
      "line_no": 2 
    },
    "order": { 
      "po_no": 'update-with-this-value' 
    } 
  }
]

When logging line-by-line it seems to set correctly, but then there is a glitch when logging after the second for loop exits.

Once the data is updated I would like to resort it with the original schema.

The issue that I'm having is that the update logic is changing all entries with the same order, and is not just updating the single line. (i.e., it is updating (set_no = 0, line_no = 1) and (set_no = 0, line_no = 2), when it should only be updating the second case.

In this case, how would I update just the second index of the normalized data set?

回答1:

I think the issue is in this line.

data[i]['items'][j]['order'] = data[i]['order']; // Set default header

change this to

data[i]['items'][j]['order'] = { ...data[i]['order'] }; // Set default header

Reason: In Javascript the objects are assigned by reference. Thus the order object was referenced in both the items. When you spread it, then it unpacks the properties into the new object created by the object literal, making a shallow copy.

来源：https://stackoverflow.com/questions/56563328/how-to-set-array-index-of-normalized-data