Querying Nested Docs

One of MongoDB's greatest strengths is its ability to handle complex, nested data. To query these fields, we use Dot Notation.

1. Querying Nested Documents

Access sub-fields by joining the field names with a dot.

// Find users lives in "NYC"
db.users.find({ "address.city": "NYC" })

// Note: Field names MUST be in quotes when using dot notation
// CORRECT: "address.city": "..."
// INCORRECT: address.city: "..."

2. Querying Arrays of Documents

When an array contains documents, you can query specific fields within those documents.

// Find blogs where at least one comment is by "Alice"
db.blogs.find({ "comments.author": "Alice" })

// Exact Match (Matches the whole document in the array)
db.blogs.find({ 
  comments: { author: "Alice", text: "Nice post!" } 
})

3. The $ Positional Operator

The `$` operator identifies an element in an array to update without specifying the element's position in the array.

// Update the score of the product "xyz" in the results array
db.survey.updateOne(
  { "results.product": "xyz" },
  { $set: { "results.$.score": 10 } }
)