MongoDB Query Documents

MongoDB Query Documents

In MongoDB, querying documents from a collection is done using the find method. This method allows you to retrieve documents that match specified criteria, enabling data extraction and analysis.

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Syntax

db.collection.find(query, projection)

The find method retrieves documents from a collection that match the query criteria. The optional projection parameter specifies the fields to return in the matching documents.

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Example MongoDB Query Documents

Let's look at some examples of how to query documents in the programGuru collection in MongoDB:

1. Query All Documents

db.programGuru.find()

This command retrieves all documents in the programGuru collection.

2. Query Documents with a Filter

db.programGuru.find({ age: { $gt: 30 } })

This command retrieves documents where the age is greater than 30.

3. Query Specific Fields

db.programGuru.find({ age: { $gt: 30 } }, { name: 1, age: 1, _id: 0 })

This command retrieves documents where the age is greater than 30, returning only the name and age fields.

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Full Example

Let's go through a complete example that includes switching to a database, creating a collection, inserting documents, querying them, and verifying the results.

Step 1: Switch to a Database

This step involves switching to a database named myDatabase.

use myDatabase

In this example, we switch to the myDatabase database.

Step 2: Create a Collection

This step involves creating a new collection named programGuru in the myDatabase database.

db.createCollection("programGuru")

Here, we create a collection named programGuru.

Step 3: Insert Documents into the Collection

This step involves inserting documents into the programGuru collection.

db.programGuru.insertMany([
    { name: "John Doe", age: 30, email: "john.doe@example.com" },
    { name: "Jane Smith", age: 25, email: "jane.smith@example.com" },
    { name: "Jim Brown", age: 35, email: "jim.brown@example.com" }
])

We insert multiple documents into the programGuru collection.

Step 4: Query Documents in the Collection

This step involves querying documents in the programGuru collection.

Query All Documents

db.programGuru.find().pretty()

We retrieve all documents in the programGuru collection.

Query Documents with a Filter

db.programGuru.find({ age: { $gt: 30 } }).pretty()

We retrieve documents where the age is greater than 30.

Query Specific Fields

db.programGuru.find({ age: { $gt: 30 } }, { name: 1, age: 1, _id: 0 }).pretty()

We retrieve documents where the age is greater than 30, returning only the name and age fields.

Conclusion

The MongoDB query documents operation is crucial for extracting and analyzing data within collections. Understanding how to query single and multiple documents, as well as specific fields, is essential for effective data retrieval in MongoDB.