@njs-lib/select-query

Overview

The library provides a flexible and powerful set of tools for querying and manipulating collections of objects in TypeScript. Whether you need to filter, paginate, or perform complex queries, this library offers an intuitive interface and extensive features.

Features

• Construct queries with a variety of comparison operators.
• Easily manipulate and filter object collections based on specific criteria.
• Perform data manipulation operations on collections.
• Calculate sums, select specific properties, and group elements by key.
• Implement pagination with methods to limit and offset the collection.
• Benefit from type safety and enhanced code completion when using TypeScript.

Installation

You can install the library using npm.

Using npm:

npm install @njs-lib/select-query --save

For more information on using npm check out the docs here.

SelectQuery Class

The SelectQuery provides utility methods for querying and manipulating collections of objects.

Constructor

new SelectQuery([])

Creates a new instance of SelectQuery with the provided collection.

• @param collection: An array of objects to be used for querying.

Methods

first(): T | undefined

Gets the first element of the collection.

const data = [
  { id: 1, name: 'Jak', age: 30 },
  { id: 2, name: 'Bob', age: 25 },
  { id: 3, name: 'Tom', age: 20 },
  { id: 4, name: 'Sam', age: 20 },
];

const result = new SelectQuery(data).first();

// RESULT { id: 1, name: 'Jak', age: 30 };

last(): T | undefined

Gets the last element of the collection.

const data = [
  { id: 1, name: 'Jak', age: 30 },
  { id: 2, name: 'Bob', age: 25 },
  { id: 3, name: 'Tom', age: 20 },
  { id: 4, name: 'Sam', age: 20 },
];

const result = new SelectQuery(data).last();

// RESULT { id: 4, name: 'Sam', age: 20 };

get(): T[]

Gets all elements in the collection.

const data = [
  { id: 1, name: 'Jak', age: 30 },
  { id: 2, name: 'Bob', age: 25 },
  { id: 3, name: 'Tom', age: 20 },
  { id: 4, name: 'Sam', age: 20 },
];

const result = new SelectQuery(data).last();

/* RESULT
[
  { id: 1, name: 'Jak', age: 30 },
  { id: 2, name: 'Bob', age: 25 },
  { id: 3, name: 'Tom', age: 20 },
  { id: 4, name: 'Sam', age: 20 },
]; 
*/

count(): number

Gets the number of elements in the collection.

const data = [
  { id: 1, name: 'Jak', age: 30 },
  { id: 2, name: 'Bob', age: 25 },
  { id: 3, name: 'Tom', age: 20 },
  { id: 4, name: 'Sam', age: 20 },
];

const result = new SelectQuery(data).count();

// RESULT 4

limit(limit: number): SelectQuery<T>

Limits the number of objects in the collection to a specified maximum.

• @param limit The maximum number of objects to include in the collection

const data = [
  { id: 1, name: 'Jak', age: 30 },
  { id: 2, name: 'Bob', age: 25 },
  { id: 3, name: 'Tom', age: 20 },
  { id: 4, name: 'Sam', age: 20 },
];

const result = new SelectQuery(data).limit(2).get();

/* RESULT 
[
  { id: 1, name: 'Jak', age: 30 },
  { id: 2, name: 'Bob', age: 25 },
]
*/

offset(offset: number): SelectQuery<T>

Offsets the collection by a specified number of objects.

• @param offset The number of objects to skip from the beginning of the collection.

const data = [
  { id: 1, name: 'Jak', age: 30 },
  { id: 2, name: 'Bob', age: 25 },
  { id: 3, name: 'Tom', age: 20 },
  { id: 4, name: 'Sam', age: 20 },
];

const result = new SelectQuery(data).offset(2).get();

/* RESULT 
[
  { id: 3, name: 'Tom', age: 20 },
  { id: 4, name: 'Sam', age: 20 },
]
*/

paginate(num: number, size: number): SelectQuery<T>

Paginates the collection based on a page number and page size.

• @param num The page number (1-based).
• @param size The number of objects per page.

const data = [
  { id: 1, name: 'Jak', age: 30 },
  { id: 2, name: 'Bob', age: 25 },
  { id: 3, name: 'Tom', age: 20 },
  { id: 4, name: 'Sam', age: 20 },
];

const result = new SelectQuery(data).paginate(2, 2).get();

/* RESULT 
[
  { id: 3, name: 'Tom', age: 20 },
  { id: 4, name: 'Sam', age: 20 },
]
*/

sum(key: K): number

Calculates the sum of the values for a specified property in the collection.

• @param key The property key whose values are to be summed up.

const data = [
  { id: 1, name: 'Jak', age: 30 },
  { id: 2, name: 'Bob', age: 25 },
  { id: 3, name: 'Tom', age: 20 },
  { id: 4, name: 'Sam', age: 20 },
];

const result = new SelectQuery(data).where('age', '===', 20).sum('age');

// RESULT 40

select(...keys: K[]): SelectQuery<Pick<T, K>>

Selects specific properties from each object in the collection and returns a new SelectQuery instance.

• @param keys The keys (properties) to select.

const data = [
  { id: 1, name: 'Jak', age: 30 },
  { id: 2, name: 'Bob', age: 25 },
  { id: 3, name: 'Tom', age: 20 },
  { id: 4, name: 'Sam', age: 20 },
];

const result = new SelectQuery(data).select('name').get();

/* RESULT
[
  { name: 'Jak' },
  { name: 'Bob' },
  { name: 'Tom' },
  { name: 'Sam' },
];
*/

keyBy(key: K): Record<T[K]), T>

Groups elements in a collection based on a specified key.

• @param key The key (property name) by which to group elements.

const data = [
  { id: 1, name: 'Jak', age: 30 },
  { id: 2, name: 'Bob', age: 25 },
  { id: 3, name: 'Tom', age: 20 },
  { id: 4, name: 'Sam', age: 20 },
];

const result = new SelectQuery(data).keyBy('id');

/* RESULT
{
  1: { id: 1, name: 'Jak', age: 30 },
  2: { id: 2, name: 'Bob', age: 25 },
  3: { id: 3, name: 'Tom', age: 20 },
  4: { id: 4, name: 'Sam', age: 20 },
};
*/

where(key: K, operator: Operator, value: T[K]): SelectQuery<T>

Filters the collection based on a specified condition.

• @param key The key (property name) to compare.
• @param operator The comparison operator.
• @param value The value to compare against.

const data = [
  { id: 1, name: 'Jak', age: 30 },
  { id: 2, name: 'Bob', age: 25 },
  { id: 3, name: 'Tom', age: 20 },
  { id: 4, name: 'Sam', age: 20 },
];

const result = new SelectQuery(data).where('id', '===', 1).get();

// RESULT [{ id: 1, name: 'Jak', age: 30 }];

const result = new SelectQuery(data).where('age', '>', 20).get();

/* RESULT
[
  { id: 1, name: 'Jak', age: 30 },
  { id: 2, name: 'Bob', age: 25 },
];
*/

static getOperators(): Operator[]

Returns an array of valid operators for comparisons.

new SelectQuery.getOperators();

// RESULT ['===', '!==', '<', '<=', '>', '>=', 'like', '^like', 'like$'];

Comparison operators

Value	Description
===	Checks if the specified property of an item is equal to a given value.
!==	Checks if the specified property of an item is not equal to a given value.
<	Checks if the specified property of an item is less than a given value.
<=	Checks if the specified property of an item is less than or equal to a given value.
>	Checks if the specified property of an item is greater than a given value.
>=	Checks if the specified property of an item is greater than or equal to a given value.
like	Checks if the specified property of value contains the given value
^like	Checks if the specified property of value starts with the given value.
like$	Checks if the specified property of value ends with the given value.

License

Released under the terms of the MIT License.