Get parent hierarchy from a child node in angular 6 material tree

Question

I am following a tutorial to implement cdk tree in angular 6. I created a tree structure, now I want to get the parent hierarchy from from the child by making it clickable, while there are methods like getDescendants to get children of a node, vice versa is not available. How can I get the parent hierarchy from a child or leaf node.

Answer 1

I've added these methods to my tree component. Note that I use the flat tree, this won't work for a nested tree.

@Component({
  selector: 'es-outline-tree',
  // ...
})
export class OutlineTreeComponent implements OnInit {
  treeControl: FlatTreeControl<FlatTreeNode>;

  // other code...

  /**
   * Recursively expand all parents of the passed node.
   */
  expandParents(node: FlatTreeNode) {
    const parent = this.getParent(node);
    this.treeControl.expand(parent);

    if (parent && parent.level > 0) {
      this.expandParents(parent);
    }
  }

  /**
   * Iterate over each node in reverse order and return the first node that has a lower level than the passed node.
   */
  getParent(node: FlatTreeNode) {
    const { treeControl } = this;
    const currentLevel = treeControl.getLevel(node);

    if (currentLevel < 1) {
      return null;
    }

    const startIndex = treeControl.dataNodes.indexOf(node) - 1;

    for (let i = startIndex; i >= 0; i--) {
      const currentNode = treeControl.dataNodes[i];

      if (treeControl.getLevel(currentNode) < currentLevel) {
        return currentNode;
      }
    }
  }
}

I'm planning to create my own FlatTreeControl (by extending Angular CDK's FlatTreeControl) and move this logic there.

UPDATE

I've moved the above logic to my own FlatTreeControl implementation:

import { FlatTreeControl } from '@angular/cdk/tree';

export class CustomTreeControl<T> extends FlatTreeControl<T> {
  /**
   * Recursively expand all parents of the passed node.
   */
  expandParents(node: T) {
    const parent = this.getParent(node);
    this.expand(parent);

    if (parent && this.getLevel(parent) > 0) {
      this.expandParents(parent);
    }
  }

  /**
   * Iterate over each node in reverse order and return the first node that has a lower level than the passed node.
   */
  getParent(node: T) {
    const currentLevel = this.getLevel(node);

    if (currentLevel < 1) {
      return null;
    }

    const startIndex = this.dataNodes.indexOf(node) - 1;

    for (let i = startIndex; i >= 0; i--) {
      const currentNode = this.dataNodes[i];

      if (this.getLevel(currentNode) < currentLevel) {
        return currentNode;
      }
    }
  }
}