Add helper function to create filter sets

src/filter.ts

@@ -15,6 +15,36 @@ export function createFilter(filterSet: FilterSet): MetadataFilter {
 	return new MetadataFilter(filterSet);
 }
 
+/**
+ * Create a filter set where each given field has given filter function(s).
+ * Useful to create a filter where multiple fields should be filtered with
+ * the same filter functions.
+ *
+ * @param fields Array of fields to filter
+ * @param filterFn Filter function or array of filter functions
+ *
+ * @return Filter set object
+ */
+export function createFilterSetForFields(
+	fields: string[],
+	filterFn: FilterFuncion | FilterFuncion[]
+): FilterSet {
+	if (!Array.isArray(fields)) {
+		throw new TypeError(
+			`Invalid 'fields' argument: expected 'string[]', got '${typeof fields}'`
+		);
+	}
+
+	if (fields.length === 0) {
+		throw new Error("Invalid 'fields' argument: received an empty array");
+	}
+
+	return fields.reduce((acc, field) => {
+		acc[field] = filterFn;
+		return acc;
+	}, {} as FilterSet);
+}
+
 /**
  * Base filter object that filters metadata fields by given filter set.
  *

test/filter.spec.ts

@@ -2,7 +2,7 @@ import chai from 'chai';
 import { expect } from 'chai';
 import spies from 'chai-spies';
 
-import { createFilter } from '../src/filter';
+import { createFilter, createFilterSetForFields } from '../src/filter';
 
 import { dummyFn } from './helper/util';
 import { testExtendedFilter } from './helper/test-filter';
@@ -154,3 +154,42 @@ describe('Test method chaining', () => {
 
 	testExtendedFilter(filter, fn1, fn2, fn3);
 });
+
+describe('Test creating filter set for fields', () => {
+	const fn1 = chai.spy(dummyFn);
+	const fn2 = chai.spy(dummyFn);
+
+	it('should throw error when received invalid argument', () => {
+		// @ts-ignore
+		expect(() => createFilterSetForFields(null, fn1)).to.throw;
+	});
+
+	it('should throw error when received empty fields array', () => {
+		expect(() => createFilterSetForFields([], fn1)).to.throw;
+	});
+
+	it('should create filter set with single functions', () => {
+		const filterSet = createFilterSetForFields(['foo', 'bar', 'baz'], fn1);
+		const expectedResult = {
+			foo: fn1,
+			bar: fn1,
+			baz: fn1,
+		};
+
+		expect(filterSet).to.be.deep.equal(expectedResult);
+	});
+
+	it('should create filter set with multiple filter functions', () => {
+		const filterSet = createFilterSetForFields(
+			['foo', 'bar', 'baz'],
+			[fn1, fn2]
+		);
+		const expectedResult = {
+			foo: [fn1, fn2],
+			bar: [fn1, fn2],
+			baz: [fn1, fn2],
+		};
+
+		expect(filterSet).to.be.deep.equal(expectedResult);
+	});
+});