CRUD and Arrays

There are a bunch of array operators. Here's some snippets of the array operators in action.

track the array throughoug the following examples.

CRUD and Arrays

Delete a value from an array with $pull

// CREATE an array at key "arrKey"
db.test.insertOne({ _id: 2, arrKey: [123, 234, 345, 456] });

// DELETE a key from that array
db.test.updateOne({ _id: 2 }, { $pull: { arrKey: { $eq: 234 } } });

Add a value if not already present with $addToSet

// ADD a val to the arr if not already present with $addToSet
db.test.updateOne({ _id: 2 }, { $addToSet: { arrKey: 'just-added' } });
db.test.findOne({ _id: 2 });
// { _id: 2, arrKey: [ 123, 345, 456, 'just-added' ] }

Remove an item from the beginning or end with $pop

db.test.updateOne({_id:2}, { $pop: { arrKey: -1  }  })
db.test.findOne({_id:2})
// { _id: 2, arrKey: [ 345, 456, 'just-added' ] }

db.test.updateOne({_id:2}, { $pop: { arrKey: 1  }  })
db.test.findOne({_id:2})
{ _id: 2, arrKey: [ 345, 456 ] }

Change the value of an array item with $set and $

// change 345 to 999
db.test.updateOne({ _id: 2, arrKey: 345 }, { $set: { 'arrKey.$': 999 } });
db.test.findOne({ _id: 2 });

Getting Nested

Create array element with $ and push

The $ operator ca be used to add an element to a nested array. Here, the $ is used in combination with $push:

// starting object in the "test" collection
[
  {
    _id: 'joe',
    wordArr: [
      {
        item: 'A',
        words: ['quick', 'brown', 'fox', 'trot'],
      },
      { item: 'B', words: ['slow', 'orange', 'goat'] },
    ],
  },
];

//
joeItemA = { _id: 'joe', 'wordArr.item': 'A' };
addPrince = { $push: { 'wordArr.$.words': 'prince' } };
Nlp > db.Themes.updateOne(joeItemA, addPrince);

Edit an Element in an array with $

findWater = { _id: 'sally', 'arrKey._id': 'water' };

Delete A Douubly-nested Element with $[]

Mongo has a few special characters. $[] is one of them. It means to update all elements in the array.
In this example, the $[] is used in combination with $pull and $eq to remove an element that equals 2:

// obj.arrKey[arrOfObjects]
insertObj = {
  _id: 'sally',
  arrKey: [
    {
      _id: 'water',
      arr: [1, 2, 3],
    },
    {
      _id: 'melon',
      arr: [4, 5, 6],
    },
  ],
};
db.test.insertOne(insertObj);

// remove the element "2" from the "water" object arr
findObj = { _id: 'sally', 'arrKey._id': 'water' };
updateObj = { $pull: { 'arrKey.$[].arr': { $eq: 2 } } };
db.test.updateOne(findObj, updateObj);

Delete an element from an array with $pull

db.Users.update({ _id: 'sally' }, { $pull: { arrKey: { _id: 'melon' } } });

Page Tags:

database

mongodb

crud

arrays