wrapper to get a list of items from DynamoDB

dydb-get-items.js

function getItems(opts) {
	passMuster(opts, {
		table: 'string',
		hashkey: 'string',
		items: 'array',
		_optional: {
			rangekey: 'string',
			rangeval: 'string',
			project: 'string'
		}
	});

	// Check that they're all truthy to avoid the `typeof null === object`
	// problem when we check the type below.
	var allTruthy = opts.items.every(function (item) {
		return !!item;
	});
	// Check based on the first item in the array passed in
	var allSameType = opts.items.every(function (item, idx, arr) {
		return typeof item === typeof arr[0];
	});
	if (!allTruthy) {
		throw new Error('getItems: All objects or hashvals passed in must be truthy.');
	}
	if (!allSameType) {
		throw new Error('getItems: All objects or hashvals passed in must be same type.');
	}

	return new Promise(function (resolve, reject) {
		// let params = {
		//  RequestItems: {
		//      users: {       <-- table name
		//          Keys: [
		//              {
		//                  HashKey: 'hashkey'
		//              },
		//          ]
		//      },
		//  }
		// Make a copy of the array passed in so we don't alter it.
		// Shouldn't be necessary since primitives are passed by value,
		// but hey, let's be safe.
		var arr = opts.items.slice();
		var arrOut = [];

		// A callback that repeatedly calls batchWrite until all of the gets have completed
		function callback(err, data) {
			if (err) {
				reject(err);
			} else {
				// console.log(data.ConsumedCapacity);
				// Save the stuff we got back to our array of results
				arrOut = arrOut.concat(data.Responses[opts.table]);
				if ('UnprocessedKeys' in data && opts.table in data.UnprocessedKeys) {
					// More data. Call again with the unprocessed items.
					var retryParams = {
						RequestItems: data.UnprocessedKeys
					};
					// console.log('Calling BatchGet again to retry ' + params.RequestItems[opts.table].length + ' UnprocessedKeys');
					docClient.batchGet(retryParams, callback);
				} else {
					if (arr.length > 0) {
						// console.log('BatchGet processed all items in the batch - going on');
						// Start another round
						doBatchGet();
					} else {
						// console.log('BatchGet processed all items in the batch - done');
						resolve(arrOut);
					}
				}
			}
		}

		function doBatchGet() {
			var params = {
				RequestItems: {},
				ReturnConsumedCapacity: 'TOTAL'
			};
			params.RequestItems[opts.table] = {
				Keys: []
			};
			if (opts.project) {
				params.RequestItems[opts.table].ProjectionExpression = opts.project;
			}

			// console.log(arr);
			for (var i = params.RequestItems[opts.table].Keys.length; i < 100; i++) {
				// Nothing else to add to the batch if the input list is empty
				if (arr.length === 0) {
					break;
				}
				var curHash = arr.pop();
				var curItem = {};
				if (opts.rangekey) {
					// Doing it this way, we can just pass in whole items
					// to the function and extract the hash or hash+range info.
					curItem[opts.hashkey] = curHash[opts.hashkey];
					curItem[opts.rangekey] = curHash[opts.rangekey];
				} else {
					curItem[opts.hashkey] = (typeof curHash === 'object') ? curHash[opts.hashkey] : curHash;
				}
				params.RequestItems[opts.table].Keys.push(curItem);
			}

			// console.log('Calling BatchGet on ' + opts.table + ' with a new batch of ' + params.RequestItems[opts.table].Keys.length + ' items');
			// console.log(params.RequestItems[opts.table].Keys[params.RequestItems[opts.table].Keys.length - 1]);
			docClient.batchGet(params, callback);
		}
		// Kick off the first run
		doBatchGet();
	});
}
// Usage:
// getItems({
//     table: 'users',
//     hashkey: 'username',
//     items: ['1', '2', '3']
// });
// or
// getItems({
//     table: 'userTask',
//     hashkey: 'username',
//     rangekey: 'taskId',
//     items: [
//         { username: '1', taskId: '1', otherAttr: 'foo' },
//         { username: '1', taskId: '2', otherAttr: 'foo' },
//         { username: '1', taskId: '3', otherAttr: 'foo' }
//     ]
// });