How to check a value in Firebase with angularfire2?

Question

I use Firebase as database, and access it through AngularFire2.
This is the whole TodoComponent.ts file so you get the full picture, but the main thing i need is in finishedTodo() .

import { Component, OnInit} from '@angular/core';
import { AngularFire, FirebaseObjectObservable ,FirebaseListObservable } from 'angularfire2';

@Component({
    template: `
<h2>ToDo</h2>

<input 
        #newTodo
        [(ngModel)]="todoinput" 
        placeholder="add ToDo" 
        (keyup.enter)="addTodo(newTodo.value)"
        type="text" 
/>  
{{ todoinput }}
<br>
{{ item | async | json }} ///here I am getting the value as a json string, but I don't know how to make it do what i need

<div *ngFor="let todo of todos | async">
    {{todo.todo}}
    <button (click)="deleteTodo(todo.$key)">Delete</button>
    <button (click)="finishedTodo(todo.$key)">Finished</button>
</div>   

    `
})

export class ToDoComponent implements OnInit{
    item: FirebaseObjectObservable<any>;
    todos: FirebaseListObservable<any>;

    constructor(private _af: AngularFire) {
    }

    ngOnInit(){
        this.todos = this._af.database.list('hr/todos');
        this.item = this._af.database.object('/hr/todos/1');
    }

    addTodo(newTodo: string){
        this.todos.push({
            todo: newTodo
        } )
    }

    deleteTodo(key: string){
        if(confirm("U sure u want to delete " + key + " ?")){
            this.todos.remove(key)
        }
    }

    finishedTodo(key: string, finished: boolean){
        this.todos.update(key,{finished: true})
    }
}

In finishedTodo() I am able to set finished = true , but before that, I want to check if the Firebase field finished = true or false , and make toggle work so I can add special css based on this condition.

The Firebase looks like this:

How can I check for finished=true value in Firebase with angularfire2?

---

Update - @Aaron Saunders Solution adapted to my file

isFinished;

finishedTodo(key: string, finished: boolean){

    var snapshotFinished = this._af.database.object('hr/todos/'+ key,{ preserveSnapshot: true})

    snapshotFinished.subscribe(snapshot => {          
        this.isFinished = snapshot.val().finished;  
    });

        if (this.isFinished == false || this.isFinished == null){
            this.todos.update(key,{finished: true});
            console.log('is false');
        }    
        else{
            this.todos.update(key,{finished: false});
            console.log('is true');
        }
}

Answer 1

   var i = this._af.database.object('/hr/todos/1', { preserveSnapshot: true })
   i.subscribe(snapshot => {
    console.log(snapshot.key)
    console.log(snapshot.val().finished)
  });

from documentation - Retrieving data as objects