Tags:

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" } } })