join-table

2019-07-13 admin

join-table是什么

什么是join-table,Collection class for many-to-many joins

join-table使用教程帮助文档

♊ join-table

NPM version CircleCI Dependency Status

Fast, mutable collection of many-to-many pairs of values.

A JoinTable instance is effectively a table of two columns (‘left’ and ‘right’). It’s similar to an ES2015 Set in that a given left-right combination can only occur once in a table.

Usage

import JoinTable from 'join-table';

const table = new JoinTable();

table.add('foo', 'bar');
table.add('foo', 'baz');
table.add('123', 456);

table.has('foo', 'bar'); // true
table.has('foo', 'baz'); // true
table.has('123', 456); // true

table.has('xxx', 'yyy'); // false
table.has('baz', 'foo'); // false (wrong order)
table.has('123', '456'); // false (strings !== integers)

table.getRightsFor('foo'); // Set {'bar', 'baz'}
table.getLeftsFor('baz');  // Set {'foo'}

API

add(left, right)

Adds a join and returns the table. Has no effect if this exact join already exists.

remove(left, right)

Removes a join and returns the table. Has no effect if this exact join does not exist.

has(left, right)

Checks if the join exists and returns true or false.

clear()

Empties the table.

getRightsFor(left)

Returns the Set of ‘right’ values that are joined with the given ‘left’ value.

getLeftsFor(right)

Returns the Set of ‘left’ values that are joined with the given ‘right’ value.

getLefts()

Returns a Set of all the ‘left’ values in the table.

getRights()

Returns a Set of all the ‘right’ values in the table.

size

The number of joins currently in the table. Note that joins are unique, so if you call .add(x, y) twice in a row, the second call will have no effect on the size.

Iterating

Join tables are iterable. Each iteration receives a two-item array in the form [left, right]:

const table = new JoinTable();

table.add('cow', 'grass');
table.add('rabbit', 'carrots');
table.add('rabbit', 'lettuce');

for (const [animal, food] of table) {
  console.log(`${animal} eats ${food}`);
}
// cow eats grass
// rabbit eats carrots
// rabbit eats lettuce

Warning: mutating the table while you’re iterating over it might have unpredictable results. If you need to update the table during a loop, you might want to spread the table into an array first:

for (const [x, y] of [...table]) {
  // safe to update table here
}

License

MIT

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