MongoDB Collection Operations: Creation, Deletion, and Data Insertion

I. What is a MongoDB Collection?¶

In MongoDB, a Collection is equivalent to a “table” in a relational database, but it stores Documents (JSON-like structures). Unlike tables, documents in a collection do not require a fixed field structure—different documents can contain different fields, making it highly flexible.

II. Creating a Collection¶

There are two ways to create a collection: explicit creation (manually via commands) and implicit creation (automatically created when inserting data).

1. Explicit Collection Creation (createCollection())¶

Use the db.createCollection(collectionName) command to manually create a collection. For example, create a collection named students:

// Execute in the MongoDB Shell
db.createCollection("students")

• If successful, it returns { "ok" : 1 }, indicating the collection was created.
• Optional Parameters: You can set collection properties like capped (fixed-size collection, old data auto-deleted) or size (maximum size in bytes). For example, create a fixed-size log collection:

  db.createCollection("logs", { capped: true, size: 10000 })

(Note: capped: true enables fixed size, and size: 10000 sets a maximum of 10KB; old data will be overwritten when exceeded.)

2. Implicit Collection Creation (Auto-created on Insert)¶

If you insert data into a non-existent collection, MongoDB automatically creates it. For example, directly insert a document into the non-existent students collection:

db.students.insertOne({ name: "Alice", age: 20 })

The students collection will be automatically created, and the inserted document will be stored.

III. Deleting a Collection (drop())¶

Use the db.collectionName.drop() command to delete a collection. This permanently removes the collection and all its data (no recycle bin), so proceed with caution!

Syntax:

db.collectionName.drop()

• Returns true if the collection exists and is successfully deleted; returns false if the collection does not exist or deletion fails.

Example:

// Delete the "students" collection
db.students.drop() // Returns true on success, false otherwise

IV. Data Insertion (insertOne()/insertMany())¶

MongoDB uses insertOne() (single document) and insertMany() (multiple documents) to insert data. Documents are in key-value pair format (similar to JSON) and automatically generate a unique _id field (customizable but recommended to use MongoDB’s auto-generated value).

1. Inserting a Single Document (insertOne())¶

Syntax:

db.collectionName.insertOne(documentObject)

• Example: Insert student information into the students collection:

  db.students.insertOne({
    name: "Bob",
    age: 22,
    major: "Computer Science",
    hobbies: ["reading", "coding"] // Array type
  })

• Return Result:

  {
    acknowledged: true,
    insertedId: ObjectId("60d21b4667d0d8992e610c85") // MongoDB auto-generated unique ID
  }

2. Inserting Multiple Documents (insertMany())¶

Syntax:

db.collectionName.insertMany([document1, document2, ...])

• Example: Insert two student records:

  db.students.insertMany([
    { name: "Charlie", age: 21, major: "Mathematics" },
    { name: "Diana", age: 23, major: "Physics", isHonorStudent: true } // New field allowed
  ])

• Return Result:

  {
    acknowledged: true,
    insertedIds: [
      ObjectId("60d21b4667d0d8992e610c86"),
      ObjectId("60d21b4667d0d8992e610c87")
    ]
  }

V. Notes¶

1. Collection Naming: Case-sensitive, and avoid special characters (except legal symbols like $ or .).
2. Data Types: Documents support flexible types: strings in quotes (e.g., name: "Bob"), numbers directly (e.g., age: 20), and dates via new Date() (e.g., birth: new Date("2000-01-01")).
3. Uniqueness: insertOne()/insertMany() auto-generate _id to ensure uniqueness within a collection (duplicate fields are allowed).
4. Irreversible Deletion: drop() permanently deletes data; back up data before deletion.

VI. Summary¶

• Create: Explicitly with createCollection(), or implicitly by inserting data.
• Delete: Use drop(), which permanently removes data with no recovery option.
• Insert: Single documents with insertOne(), multiple documents with insertMany(), using key-value pair format.

With these operations, you’ve mastered the basics of collection management and data insertion in MongoDB. Try practicing in the MongoDB Shell or a visualization tool (e.g., Robo 3T) to reinforce your understanding!