feat: avoid instantiating DocumentClient

This refactor avoids instantiating a DynamoDB.DocumentClient object
(which in turn would instantiate an underlying DynamoDB service client)
by accessing the `createSet` method from the prototype directly.

The interface for `createSet` is:

```typescript
    createSet(list: number[]|string[]|DocumentClient.binaryType[], options?: DocumentClient.CreateSetOptions): DocumentClient.DynamoDbSet;
```

And the implementation is:

```typescript
  createSet: function(list, options) {
    options = options || {};
    return new DynamoDBSet(list, options);
  }
```

As we can see, there is no reliance on the `this` instance, so calling
the method from the prototype with an undefined `this` value should work
fine. It would have perhaps been preferred to utilize the `DynamoDBSet`
class directly, but that is marked with `@private` annotations within
the AWS SDK while the `createSet` method on DocumentClient is part of
the public API.

Aside from the removal of client instantiation, this change also scopes
imports to just the DynamoDB specific resources. This has been measured
to improve performance by several milliseconds in Lambda runtimes.

This somewhat relates to issue #29, but it doesn't really address it.

src/index.test.ts

@@ -1,5 +1,4 @@
-import AWS from 'aws-sdk';
-
+import { DocumentClient } from 'aws-sdk/clients/dynamodb';
 import type { DynoexprOutput } from './dynoexpr';
 import dynoexpr from '.';
 
@@ -23,13 +22,13 @@ describe('high level API', () => {
 
 	it('accepts a type to be applied to the output', () => {
 		expect.assertions(1);
-		const params = dynoexpr<AWS.DynamoDB.DocumentClient.UpdateItemInput>({
+		const params = dynoexpr<DocumentClient.UpdateItemInput>({
 			TableName: 'Table',
 			Key: 123,
 			UpdateSet: { color: 'pink' },
 		});
 
-		assertType<AWS.DynamoDB.DocumentClient.ScanInput, typeof params>();
+		assertType<DocumentClient.ScanInput, typeof params>();
 		expect(params.Key).toBe(123);
 	});
 });

src/operations/single.test.ts

@@ -1,13 +1,10 @@
-import AWS from 'aws-sdk';
-
 import type { DynoexprInput, DynoexprOutput } from '../dynoexpr';
 import {
+	createDynamoDbSet,
 	getSingleTableExpressions,
 	convertValuesToDynamoDbSet,
 } from './single';
 
-const docClient = new AWS.DynamoDB.DocumentClient();
-
 describe('single table operations', () => {
 	it('applies consecutive expression getters to a parameters object', () => {
 		const params: DynoexprInput = {
@@ -154,6 +151,53 @@ describe('single table operations', () => {
 		expect(result).toStrictEqual(expected);
 	});
 
+	it('creates DynamoDBSet instances for strings', () => {
+		const params = ['hello', 'world'];
+		const result = createDynamoDbSet(params);
+		expect(result.type).toBe('String');
+		expect(result.values).toHaveLength(params.length);
+		expect(result.values).toContain('hello');
+		expect(result.values).toContain('world');
+	});
+
+	it('creates DynamoDBSet instances for numbers', () => {
+		const params = [42, 1, 2];
+		const result = createDynamoDbSet(params);
+		expect(result.type).toBe('Number');
+		expect(result.values).toHaveLength(params.length);
+		expect(result.values).toContain(42);
+		expect(result.values).toContain(1);
+		expect(result.values).toContain(2);
+	});
+
+	it('creates DynamoDBSet instances for binary types', () => {
+		const params = [
+			Buffer.from([0x62, 0x75, 0x66, 0x66, 0x65, 0x72]),
+			Buffer.from([0x61, 0x62, 0x63]),
+		];
+		const result = createDynamoDbSet(params);
+		expect(result.type).toBe('Binary');
+		expect(result.values).toHaveLength(params.length);
+		expect(result.values).toContainEqual(params[0]);
+		expect(result.values).toContain(params[1]);
+	});
+
+	it('does not throw an error with mixed set types if validation is not explicitly enabled', () => {
+		const params = ['hello', 42];
+		const result = createDynamoDbSet(params);
+		expect(result.type).toBe('String');
+		expect(result.values).toHaveLength(params.length);
+		expect(result.values).toContain('hello');
+		expect(result.values).toContain(42);
+	});
+
+	it('throws an error with mixed set types if validation is enabled', () => {
+		const params = ['hello', 42];
+		const expression = () => createDynamoDbSet(params, { validate: true });
+		const expectedErrorMessage = 'String Set contains Number value';
+		expect(expression).toThrow(expectedErrorMessage);
+	});
+
 	it('converts Sets to DynamoDbSet if present in ExpressionsAttributeValues', () => {
 		const values = {
 			a: 1,
@@ -170,8 +214,8 @@ describe('single table operations', () => {
 			b: 'foo',
 			c: [1, 2, 3],
 			d: { foo: 'bar' },
-			e: docClient.createSet([1, 2]),
-			f: docClient.createSet(['foo', 'bar']),
+			e: createDynamoDbSet([1, 2]),
+			f: createDynamoDbSet(['foo', 'bar']),
 		};
 		expect(result).toStrictEqual(expected);
 	});

src/operations/single.ts

@@ -1,4 +1,4 @@
-import AWS from 'aws-sdk';
+import { DocumentClient } from 'aws-sdk/clients/dynamodb';
 
 import type { DynoexprInput, DynamoDbValue, DynoexprOutput } from '../dynoexpr';
 import { getConditionExpression } from '../expressions/condition';
@@ -10,7 +10,8 @@ import { getKeyConditionExpression } from '../expressions/key-condition';
 
 import { trimEmptyExpressionAttributes } from './helpers';
 
-const docClient = new AWS.DynamoDB.DocumentClient();
+export const createDynamoDbSet =
+	DocumentClient.prototype.createSet.bind(undefined);
 
 type ConvertValuesToDynamoDbSetFn = (
 	attributeValues: Record<string, unknown>
@@ -20,7 +21,7 @@ export const convertValuesToDynamoDbSet: ConvertValuesToDynamoDbSetFn = (
 ) =>
 	Object.entries(attributeValues).reduce((acc, [key, value]) => {
 		if (value instanceof Set) {
-			acc[key] = docClient.createSet(Array.from(value));
+			acc[key] = createDynamoDbSet(Array.from(value));
 		} else {
 			acc[key] = value as DynamoDbValue;
 		}