datastore: support streaming gets

Author: stephenplusplus

lib/datastore/request.js

@@ -25,6 +25,7 @@ var request = require('request').defaults({
     maxSockets: Infinity
   }
 });
+var through = require('through2');
 
 /**
  * @type {module:datastore/entity}
@@ -92,11 +93,13 @@ function DatastoreRequest() {}
  * transaction. Get operations require a valid key to retrieve the
  * key-identified entity from Datastore.
  *
+ * @throws {Error} If at least one Key object is not provided.
+ *
  * @param {Key|Key[]} keys - Datastore key object(s).
  * @param {function} callback - The callback function.
  * @param {?error} callback.err - An error returned while making this request
  * @param {module:datastore/entity|module:datastore/entity[]} callback.entity -
- *     Will return either a single Entity or a list of Entities
+ *     Will return either a single Entity or a list of Entities.
  * @param {object} callback.apiResponse - The full API response.
  *
  * @example
@@ -105,57 +108,98 @@ function DatastoreRequest() {}
  * // your use, whether that be a Dataset or Transaction object.
  * //-
  *
+ * //-
  * // Get a single entity.
+ * //-
  * var key = dataset.key(['Company', 123]);
+ *
  * transaction.get(key, function(err, entity, apiResponse) {});
  *
- * // Get multiple entities at once.
- * transaction.get([
+ * //-
+ * // Get multiple entities at once with a callback.
+ * //-
+ * var keys = [
  *   dataset.key(['Company', 123]),
  *   dataset.key(['Product', 'Computer'])
- * ], function(err, entities, apiResponse) {});
+ * ];
+ *
+ * transaction.get(keys, function(err, entities, apiResponse) {});
+ *
+ * //-
+ * // Or, get the entities as a readable object stream.
+ * //-
+ * transaction.get(keys)
+ *   .on('error', function(err, apiResponse) {})
+ *   .on('data', function(entity) {
+ *     // entity is an entity object.
+ *   })
+ *   .on('end', function() {
+ *     // All entities retrieved.
+ *   });
  */
 DatastoreRequest.prototype.get = function(keys, callback) {
-  var that = this;
+  var self = this;
 
-  var isMultipleRequest = Array.isArray(keys);
-  keys = isMultipleRequest ? keys : [keys];
+  var isStreamMode = !callback;
+  var stream;
 
-  callback = callback || util.noop;
+  if (isStreamMode) {
+    stream = through.obj();
+  }
 
-  var req = {
-    key: keys.map(entity.keyToKeyProto)
+  var isSingleLookup = !util.is(keys, 'array');
+  keys = util.arrayize(keys).map(entity.keyToKeyProto);
+
+  if (keys.length === 0) {
+    throw new Error('At least one Key object is required.');
+  }
+
+  var request = {
+    key: keys
   };
 
-  this.makeReq_('lookup', req, function(err, resp) {
+  var entities = [];
+  this.makeReq_('lookup', request, onApiResponse);
+
+  function onApiResponse(err, resp) {
     if (err) {
-      callback(err, null, resp);
+      if (isStreamMode) {
+        stream.emit('error', err, resp);
+        stream.end();
+      } else {
+        callback(err, null, resp);
+      }
       return;
     }
 
-    var found = entity.formatArray(resp.found);
-
-    if (isMultipleRequest && resp.deferred && resp.deferred.length) {
-      // There may be more results. Call `.get` again, and append the results.
-      that.get(
-          resp.deferred.map(entity.keyFromKeyProto), function(err, entities) {
-        if (err) {
-          callback(err, null, resp);
-          return;
-        }
-
-        if (resp) {
-          found = (found || []).concat(entities);
-        }
+    var results = entity.formatArray(resp.found);
 
-        callback(null, found, resp);
+    if (isStreamMode) {
+      results.forEach(function(entity) {
+        stream.push(entity);
       });
+    } else {
+      entities = entities.concat(results);
+    }
+
+    var nextKeys = (resp.deferred || []).map(entity.keyFromKeyProto);
 
+    if (nextKeys.length > 0) {
+      self.get(nextKeys, onApiResponse);
       return;
     }
 
-    callback(null, isMultipleRequest ? found : found[0], resp);
-  });
+    if (isStreamMode) {
+      stream.push(null);
+      stream.end();
+    } else {
+      callback(null, isSingleLookup ? entities[0] : entities, resp);
+    }
+  }
+
+  if (isStreamMode) {
+    return stream;
+  }
 };
 
 /**

system-test/datastore.js

@@ -183,6 +183,33 @@ describe('datastore', function() {
       });
     });
 
+    it('should get multiple entities in a stream', function(done) {
+      var key1 = ds.key('Post');
+      var key2 = ds.key('Post');
+
+      ds.save([
+        { key: key1, data: post },
+        { key: key2, data: post }
+      ], function(err) {
+        assert.ifError(err);
+
+        var firstKey = ds.key(['Post', key1.path[1]]);
+        var secondKey = ds.key(['Post', key2.path[1]]);
+
+        var numEntitiesEmitted = 0;
+
+        ds.get([firstKey, secondKey])
+          .on('error', done)
+          .on('data', function() {
+            numEntitiesEmitted++;
+          })
+          .on('end', function() {
+            assert.strictEqual(numEntitiesEmitted, 2);
+
+            ds.delete([firstKey, secondKey], done);
+          });
+      });
+    });
   });
 
   it('should save keys as a part of entity and query by key', function(done) {