wrap

TypeScript only

rel.wrap(['a', 'b', ...], 'wrapped')

Problem

Combine multiple attributes into a single tuple-valued attribute.

Example: I want to group address fields (street, city, zip) into a single address object.

Description

The wrap operator takes specified attributes and combines them into a single nested object attribute. This is the inverse of unwrap.

Parameters:

• First argument: Array of attribute names to wrap
• Second argument: Name of the new nested attribute

Requirements

The specified attributes must exist in the input relation.

Examples

Basic wrap

const flat = Bmg([
  { id: 1, name: "Alice", city: "London", country: "UK" },
  { id: 2, name: "Bob", city: "Paris", country: "France" }
])

flat.wrap(['city', 'country'], 'address').toArray()

// =>
// [{ id: 1, name: "Alice", address: { city: "London", country: "UK" } },
//  { id: 2, name: "Bob", address: { city: "Paris", country: "France" } }]

Preparing for JSON output

const order = Bmg([
  { order_id: 1, product: "Widget",
    shipping_street: "123 Main St", shipping_city: "London", shipping_zip: "SW1" }
])

order
  .wrap(['shipping_street', 'shipping_city', 'shipping_zip'], 'shipping')
  .toArray()

// =>
// [{ order_id: 1, product: "Widget",
//    shipping: { shipping_street: "123 Main St", shipping_city: "London", shipping_zip: "SW1" } }]

Comparison with group

Operator	Result
wrap	Creates a single tuple-valued attribute from multiple attributes
group	Creates a relation-valued attribute (collection of tuples)

Use wrap when you want to nest attributes into an object. Use group when you want to create nested collections.