# Manipulating Data in Firestore

While, a majority of the time, data will only be retrieved from a Firestore database, it is still necessary to manipulated the data from time to time. This includes adding new documents, updating existing documents, and deleting documents.

# Adding Documents

The add() method is used to add a new document to an existing collection. The method is applied to a collection reference, and receive an object for its data. The add() method returns a Promise, which will result in the document that was just added.

db.collection('restaurants')
  .add({
    name: this.name,
    city: this.city
  })
  .then(doc => { console.log(doc.id) })

# Updating Documents

The update() method is used to update one or more fields of an existing document. The method is applied to a document reference, and receives an object of the update data. Only properties in the passed object will be updated, any additional properties will left unchanged. A callback function can be added to execute after the document has been updated.

db.collection('restaurants').doc(this.id)
  .update({
    name: this.name,
    city: this.city
  })
  .then(() => { console.log('The document has been updated') })

# Deleting Documents

The delete() method is used to delete existing documents. The method is applied to a document reference. A callback function can be added to execute after the document has been deleted.

db.collection('restaurants').doc(this.id)
  .delete()
  .then(() => { console.log('The document has been deleted') })