REPLACING A DOCUMENT IN MONGODB

Replacing a document in MongoDB involves using the replaceOne() method. This method requires three parameters: filter, replacement, and options.

• filter: This is a query that identifies the document you want to replace.
• replacement: It’s the new document that will replace the old one.
• options: An object where you can specify various options for the update operation.

In the example code below, we are using the _id field to filter the document. The replacement document contains the data that should be inserted in place of the old document:

db.books.replaceOne(
  {
    _id: ObjectId("6282afeb441a74a98dbbec4e"),
  },
  {
    title: "Data Science Fundamentals for Python and MongoDB",
    isbn: "1484235967",
    publishedDate: new Date("2018-5-10"),
    thumbnailUrl:
      "https://m.media-amazon.com/images/I/71opmUBc2wL._AC_UY218_.jpg",
    authors: ["David Paper"],
    categories: ["Data Science"],
  }
)

Explanation: In this example, we are replacing a document in the “books” collection based on its _id. The new document provided in the replacement parameter will entirely replace the existing document.

UPDATING MONGODB DOCUMENTS BY USING updateOne()

The updateOne() method allows you to update documents in MongoDB by providing a filter document, an update document, and an optional options object. MongoDB provides several update operators and options for more flexible updates. We will explore three of them: $set, upsert, and $push.

$set Operator

The $set operator replaces the value of a field with the specified value. Here’s an example:

db.podcasts.updateOne(
  {
    _id: ObjectId("5e8f8f8f8f8f8f8f8f8f8f8"),
  },
  {
    $set: {
      subscribers: 98562,
    },
  }
)

Explanation: This query uses the $set operator to update the “subscribers” field in a document from the “podcasts” collection. The field’s value will be replaced with 98562.

upsert Option

The upsert option is used to create a new document if no documents match the specified criteria. Example:

db.podcasts.updateOne(
  { title: "The Developer Hub" },
  { $set: { topics: ["databases", "MongoDB"] } },
  { upsert: true }
)

Explanation: If there is no document with the title “The Developer Hub,” this operation will create a new document with the specified fields and values. The upsert option enables this behavior.

$push Operator

The $push operator adds a new value to an array field. Example:

db.podcasts.updateOne(
  { _id: ObjectId("5e8f8f8f8f8f8f8f8f8f8f8") },
  { $push: { hosts: "Nic Raboy" } }
)

Explanation: This query uses the $push operator to add a new value (“Nic Raboy”) to the “hosts” array field in a document from the “podcasts” collection.

UPDATING MONGODB DOCUMENTS BY USING findAndModify()

The findAndModify() method allows you to find and replace a single document in MongoDB. It accepts a query document, an update document, and an optional options object. By default, it returns the unmodified document before updating it. When using upsert, it can also insert a new document if no matches are found.

Here’s an example:

db.podcasts.findAndModify({
  query: { _id: ObjectId("6261a92dfee1ff300dc80bf1") },
  update: { $inc: { subscribers: 1 } },
  new: true,
  upsert: true,
})

Explanation: In this example, we use findAndModify() to increment the “subscribers” field of a document from the “podcasts” collection. If no document with the specified _id is found, it will insert a new one due to the upsert: true option.

UPDATING MONGODB DOCUMENTS BY USING updateMany()

To update multiple documents, you can use the updateMany() method. This method accepts a filter document, an update document, and an optional options object.

Here’s an example:

db.books.updateMany(
  { publishedDate: { $lt: new Date("2019-01-01") } },
  { $set: { status: "LEGACY" } }
)

Explanation: In this example, we use updateMany() to set the “status” field to “LEGACY” for all documents in the “books” collection where the “publishedDate” is earlier than January 1, 2019.

DELETING DOCUMENTS IN MONGODB

To delete documents in MongoDB, you can use either the deleteOne() or deleteMany() methods. Both methods require a filter document to specify which documents to delete.

Delete One Document

Here’s an example of using the deleteOne() method to delete a single document:

db.podcasts.deleteOne({ _id: Objectid("6282c9862acb966e76bbf20a") })

Explanation: This operation deletes a single document from the “podcasts” collection based on its _id.

Delete Many Documents

The deleteMany() method is used to delete multiple documents that match the specified filter:

db.podcasts.deleteMany({ category: "crime" })

Explanation: This operation deletes all documents from the “podcasts” collection where the “category” field is equal to “crime”.