Assignments Of Day 8: MongoDB CRUD Operations – Part 4 (Delete)

Assignments Of Day 8: MongoDB CRUD Operations – Part 4 (Delete)

Assignment 1: Delete a Document by Name

Task:
Delete a student named "Emma" from the students collection.

Solution:

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db.students.deleteOne({ name: "Emma" })

Explanation:

• The filter { name: "Emma" } matches the first document where the name field equals "Emma".
• The deleteOne() method removes this document from the collection.

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Assignment 2: Delete Documents by Age

Task:
Delete all students who are 20 years old from the students collection.

Solution:

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db.students.deleteMany({ age: 20 })

Explanation:

• The filter { age: 20 } matches all documents where the age field is 20.
• The deleteMany() method removes all matching documents.

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Assignment 3: Delete Documents with Marks Below a Threshold

Task:
Delete all students who scored less than 40 marks in the students collection.

Solution:

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db.students.deleteMany({ marks: { $lt: 40 } })

Explanation:

• The filter { marks: { $lt: 40 } } uses the $lt operator to match documents where the marks field is less than 40.
• The deleteMany() method removes all such documents.

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Assignment 4: Delete Documents Based on Multiple Conditions

Task:
Delete all students who are 18 years old and enrolled in the "Math" course.

Solution:

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db.students.deleteMany({ age: 18, course: "Math" })

Explanation:

• The filter { age: 18, course: "Math" } matches documents where both conditions are true.
• The deleteMany() method removes all documents meeting these criteria.

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Assignment 5: Delete Documents with Specific IDs

Task:
Delete the document with the _id of ObjectId("64a7c5f8e9d1a74c12345678").

Solution:

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db.students.deleteOne({ _id: ObjectId("64a7c5f8e9d1a74c12345678") })

Explanation:

• The _id field is a unique identifier, and we use it to target a specific document.
• The ObjectId() function ensures the ID is correctly formatted for the query.

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Assignment 6: Delete All Documents in a Collection

Task:
Clear all records in the temporary_data collection.

Solution:

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db.temporary_data.deleteMany({})

Explanation:

• An empty filter {} matches all documents in the collection.
• The deleteMany() method deletes every document.

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Assignment 7: Delete Documents with Embedded Fields

Task:
Delete all students with an address field where the city is "New York."

Solution:

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db.students.deleteMany({ "address.city": "New York" })

Explanation:

• The filter "address.city": "New York" accesses the city field inside the address embedded document.
• The deleteMany() method removes all documents where this condition is met.

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Assignment 8: Delete Documents Using a Range Condition

Task:
Delete all students whose ages are between 15 and 20 (inclusive).

Solution:

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db.students.deleteMany({ age: { $gte: 15, $lte: 20 } })

Explanation:

• The filter { age: { $gte: 15, $lte: 20 } } uses the $gte (greater than or equal to) and $lte (less than or equal to) operators to match the range.
• The deleteMany() method removes all documents satisfying this range condition.

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Assignment 9: Delete Documents with a Field Missing

Task:
Delete all students where the phone field does not exist.

Solution:

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db.students.deleteMany({ phone: { $exists: false } })

Explanation:

• The filter { phone: { $exists: false } } matches documents where the phone field is missing.
• The deleteMany() method removes all such documents.

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Assignment 10: Verify Deletion Using Result

Task:
Delete all students in the "Physics" course and print the number of documents deleted.

Solution:

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const result = db.students.deleteMany({ course: "Physics" });

print(`Documents deleted: ${result.deletedCount}`);

Explanation:

1.  The filter { course: "Physics" } matches all documents where the course field equals "Physics".

2.  The deleteMany() method removes these documents and returns a result object.

3.  The deletedCount field in the result object shows the number of documents deleted.

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Summary Table

Task	Method	Filter Example
Delete a document by name	deleteOne	{ name: "Emma" }
Delete documents by age	deleteMany	{ age: 20 }
Delete documents with marks below 40	deleteMany	{ marks: { $lt: 40 } }
Delete documents with multiple conditions	deleteMany	{ age: 18, course: "Math" }
Delete by _id	deleteOne	{ _id: ObjectId("id_value") }
Delete all documents in a collection	deleteMany	{}
Delete documents with embedded fields	deleteMany	{ "address.city": "New York" }
Delete documents by range	deleteMany	{ age: { $gte: 15, $lte: 20 } }
Delete documents with missing fields	deleteMany	{ phone: { $exists: false } }
Verify deletion count	deleteMany	{ course: "Physics" }

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