Get parent of child node in angular material nested tree

If you want to get the whole parent hierarchy, at click on a child node, my solution is to use a recursive function:

onLeafNodeClick(node) {
  const ancestors = getAncestors(this.dataSource.data, node.name);
}

getAncestors(array, name) {
  if (typeof array !== 'undefined') {
    for (let i = 0; i < array.length; i++) {
      if (array[i].name === name) {
        return [array[i]];
      }
      const a = this.getAncestors(array[i].children, name);
      if (a !== null) {
        a.unshift(array[i]);
        return a;
      }
    }
  }
  return null;
}

This will return a new array, having at index 0 the root item, and at index n-1 the child node that has been clicked.

Working example:

https://stackblitz.com/edit/angular-r7rxyl-vwdlhy?file=app/tree-nested-overview-example.ts

The direct parent of the node will be:

const directParent = ancestors[ancestors.length - 2];

You can use this array to display breadcrumbs (root/child_1/child_2):

let breadcrumbs = '';
ancestors.forEach(ancestor => {
  breadcrumbs += `${ancestor.name}/`;
});

If you just want to get some attributes of the parent element (eg: parent name, parent id), my solution is to process the original data before assigning it to mat-tree data source. We can add a new property on each node, parent, which will be an object that stores the desired attributes of the parent element.

The code will be:

this.dataSource.data = this._processData(TREE_DATA);

_processData(data, parent = null) {
  data.forEach(item => {
    if (parent !== null) {
      item.parent = {name: parent.name};
    } else {
      item.parent = null;
    }
    if (item.children) {
      this._processData(item.children, item);
    }
  });
  return data;
}

Example leaf node after data processing:

{
  name: "Apple", 
  parent: {
    name: "Fruit"
  }
}

Working example:

https://stackblitz.com/edit/angular-r7rxyl?file=app%2Ftree-nested-overview-example.ts