Get Object by Id()

Find object by id in an array of JavaScript objects

Use the find() method:

myArray.find(x => x.id === '45').foo;

From MDN:

The find() method returns the first value in the array, if an element in the array satisfies the provided testing function. Otherwise undefined is returned.

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If you want to find its index instead, use findIndex():

myArray.findIndex(x => x.id === '45');

From MDN:

The findIndex() method returns the index of the first element in the array that satisfies the provided testing function. Otherwise -1 is returned.

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If you want to get an array of matching elements, use the filter() method instead:

myArray.filter(x => x.id === '45');

This will return an array of objects. If you want to get an array of foo properties, you can do this with the map() method:

myArray.filter(x => x.id === '45').map(x => x.foo);

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Side note: methods like find() or filter(), and arrow functions are not supported by older browsers (like IE), so if you want to support these browsers, you should transpile your code using Babel (with the polyfill).

How do I search for an object by its ObjectId in the mongo console?

Not strange at all, people do this all the time. Make sure the collection name is correct (case matters) and that the ObjectId is exact.

Documentation is here

> db.test.insert({x: 1})

> db.test.find()                                               // no criteria
{ "_id" : ObjectId("4ecc05e55dd98a436ddcc47c"), "x" : 1 }      

> db.test.find({"_id" : ObjectId("4ecc05e55dd98a436ddcc47c")}) // explicit
{ "_id" : ObjectId("4ecc05e55dd98a436ddcc47c"), "x" : 1 }

> db.test.find(ObjectId("4ecc05e55dd98a436ddcc47c"))           // shortcut
{ "_id" : ObjectId("4ecc05e55dd98a436ddcc47c"), "x" : 1 }

Get java object by id

Use HashMap to keep objects. Then use the get method to get the object with the given id.

public class Forest {
    public String forestName;

    HashMap<Integer, Tree> trees = new HashMap<>();

    public Forest(String forestName){
        this.forestName=forestName;

        //initialize trees
        trees.put(4, new Tree(4, "redleaef"));
    }

    public void updateTreeName(int id, String Name){
        trees.get(id).treeName = Name;
    }

    public static void main(String[] args) {
        Forest greenforest = new Forest("name");
        // create some tree's in the greenforest.
        greenforest.updateTreeName(4, "red leafe");
    }
}

How to get data by id from an object

You can use Array#find function and pass a condition into it like

arr.find(item => item.id === 1)

Example

const users = [

  {id: 1, name: 'A'},

  {id: 2, name: 'B'},

];

const user = users.find(item => item.id === 1);

console.log(user);

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