feat(collection): Implement new count API

Deprecate count, implement and test countDocuments
and estimatedDocumentCount

Fixes NODE-1501

lib/collection.js

@@ -1829,6 +1829,7 @@ var indexInformation = function(self, options, callback) {
  * @param {ClientSession} [options.session] optional session to use for this operation
  * @param {Collection~countCallback} [callback] The command result callback
  * @return {Promise} returns Promise if no callback passed
+ * @deprecated use countDocuments or estimatedDocumentCount instead
  */
 Collection.prototype.count = function(query, options, callback) {
   var args = Array.prototype.slice.call(arguments, 0);
@@ -1839,19 +1840,36 @@ Collection.prototype.count = function(query, options, callback) {
   return executeOperation(this.s.topology, count, [this, query, options, callback]);
 };
 
-var count = function(self, query, options, callback) {
-  var skip = options.skip;
-  var limit = options.limit;
-  var hint = options.hint;
-  var maxTimeMS = options.maxTimeMS;
+/**
+ * Gets an estimate of the count of documents in a collection using collection metadata.
+ * @method
+ * @param {object} [options] Optional settings.
+ * @param {number} [options.maxTimeMS] The maximum amount of time to allow the operation to run.
+ * @param {Collection~countCallback} [callback] The command result callback.
+ * @return {Promise} returns Promise if no callback passed.
+ */
+Collection.prototype.estimatedDocumentCount = function(options, callback) {
+  if (typeof options === 'function') (callback = options), (options = {});
+  options = options || {};
 
-  // Final query
-  var cmd = {
-    count: self.s.name,
+  options = typeof options.maxTimeMS === 'number' ? options : {};
+
+  return executeOperation(this.s.topology, count, [this, null, options, callback]);
+};
+
+const count = function(collection, query, options, callback) {
+  const skip = options.skip;
+  const limit = options.limit;
+  const hint = options.hint;
+  const maxTimeMS = options.maxTimeMS;
+  query = query || {};
+
+  const cmd = {
+    count: collection.s.name,
     query: query
   };
 
-  // Add limit, skip and maxTimeMS if defined
+  // Add skip, limit, maxTimeMS, and hint if defined
   if (typeof skip === 'number') cmd.skip = skip;
   if (typeof limit === 'number') cmd.limit = limit;
   if (typeof maxTimeMS === 'number') cmd.maxTimeMS = maxTimeMS;
@@ -1860,21 +1878,74 @@ var count = function(self, query, options, callback) {
   options = shallowClone(options);
 
   // Ensure we have the right read preference inheritance
-  options = getReadPreference(self, options, self.s.db);
+  options = getReadPreference(collection, options, collection.s.db);
 
   // Do we have a readConcern specified
-  decorateWithReadConcern(cmd, self, options);
+  decorateWithReadConcern(cmd, collection, options);
 
   // Have we specified collation
-  decorateWithCollation(cmd, self, options);
+  decorateWithCollation(cmd, collection, options);
 
   // Execute command
-  self.s.db.command(cmd, options, function(err, result) {
+  collection.s.db.command(cmd, options, function(err, result) {
     if (err) return handleCallback(callback, err);
     handleCallback(callback, null, result.n);
   });
 };
 
+/**
+ * Gets the number of documents matching the filter.
+ * @param {object} [query] the query for the count
+ * @param {object} [options] Optional settings.
+ * @param {object} [options.collation] Specifies a collation.
+ * @param {string|object} [options.hint] The index to use.
+ * @param {number} [options.limit] The maximum number of document to count.
+ * @param {number} [options.maxTimeMS] The maximum amount of time to allow the operation to run.
+ * @param {number} [options.skip] The number of documents to skip before counting.
+ * @param {Collection~countCallback} [callback] The command result callback.
+ * @return {Promise} returns Promise if no callback passed.
+ */
+
+Collection.prototype.countDocuments = function(query, options, callback) {
+  var args = Array.prototype.slice.call(arguments, 0);
+  callback = typeof args[args.length - 1] === 'function' ? args.pop() : undefined;
+  query = args.length ? args.shift() || {} : {};
+  options = args.length ? args.shift() || {} : {};
+
+  return executeOperation(this.s.topology, countDocuments, [this, query, options, callback]);
+};
+
+const countDocuments = function(collection, query, options, callback) {
+  const skip = options.skip;
+  const limit = options.limit;
+  options = Object.assign({}, options);
+
+  const pipeline = [{ $match: query }];
+
+  // Add skip and limit if defined
+  if (typeof skip === 'number') {
+    pipeline.push({ $skip: skip });
+  }
+
+  if (typeof limit === 'number') {
+    pipeline.push({ $limit: limit });
+  }
+
+  pipeline.push({ $group: { _id: null, n: { $sum: 1 } } });
+
+  delete options.limit;
+  delete options.skip;
+
+  // TODO: look out for how this plays into operations refactor
+  collection.aggregate(pipeline, options, function(err, result) {
+    if (err) return handleCallback(callback, err);
+    result
+      .toArray()
+      .then(docs => handleCallback(callback, null, docs[0].n))
+      .catch(e => handleCallback(e));
+  });
+};
+
 /**
  * The distinct command returns returns a list of distinct values for the given key across a collection.
  * @method

test/functional/crud_spec_tests.js

@@ -38,16 +38,21 @@ describe('CRUD spec', function() {
       const scenario = scenarioData[1];
       scenario.name = scenarioName;
 
+      const metadata = {
+        requires: {
+          topology: ['single', 'replicaset', 'sharded']
+        }
+      };
+
+      if (scenario.minServerVersion) {
+        metadata.requires.mongodb = `>=${scenario.minServerVersion}`;
+      }
+
       describe(scenarioName, function() {
         scenario.tests.forEach(scenarioTest => {
           beforeEach(() => testContext.db.dropDatabase());
           it(scenarioTest.description, {
-            metadata: {
-              requires: {
-                topology: ['single', 'replicaset', 'sharded'],
-                mongodb: `>=${scenario.minServerVersion}`
-              }
-            },
+            metadata,
             test: function() {
               return executeScenario(scenario, scenarioTest, this.configuration, testContext);
             }
@@ -63,17 +68,22 @@ describe('CRUD spec', function() {
       const scenario = scenarioData[1];
       scenario.name = scenarioName;
 
+      const metadata = {
+        requires: {
+          topology: ['single', 'replicaset', 'sharded']
+        }
+      };
+
+      if (scenario.minServerVersion) {
+        metadata.requires.mongodb = `>=${scenario.minServerVersion}`;
+      }
+
       describe(scenarioName, function() {
         beforeEach(() => testContext.db.dropDatabase());
 
         scenario.tests.forEach(scenarioTest => {
           it(scenarioTest.description, {
-            metadata: {
-              requires: {
-                topology: ['single', 'replicaset', 'sharded'],
-                mongodb: `>=${scenario.minServerVersion}`
-              }
-            },
+            metadata,
             test: function() {
               return executeScenario(scenario, scenarioTest, this.configuration, testContext);
             }
@@ -120,6 +130,27 @@ describe('CRUD spec', function() {
       .then(result => test.equal(result, scenarioTest.outcome.result));
   }
 
+  function executeCountDocumentsTest(scenarioTest, db, collection) {
+    const args = scenarioTest.operation.arguments;
+    const filter = args.filter;
+    const options = Object.assign({}, args);
+    delete options.filter;
+
+    return collection
+      .countDocuments(filter, options)
+      .then(result => test.equal(result, scenarioTest.outcome.result));
+  }
+
+  function executeEstimatedDocumentCountTest(scenarioTest, db, collection) {
+    const args = scenarioTest.operation.arguments;
+    const options = Object.assign({}, args);
+    delete options.filter;
+
+    return collection
+      .estimatedDocumentCount(options)
+      .then(result => test.equal(result, scenarioTest.outcome.result));
+  }
+
   function executeDistinctTest(scenarioTest, db, collection) {
     const args = scenarioTest.operation.arguments;
     const fieldName = args.fieldName;
@@ -326,6 +357,10 @@ describe('CRUD spec', function() {
             return executeAggregateTest(scenarioTest, context.db, collection);
           case 'count':
             return executeCountTest(scenarioTest, context.db, collection);
+          case 'countDocuments':
+            return executeCountDocumentsTest(scenarioTest, context.db, collection);
+          case 'estimatedDocumentCount':
+            return executeEstimatedDocumentCountTest(scenarioTest, context.db, collection);
           case 'distinct':
             return executeDistinctTest(scenarioTest, context.db, collection);
           case 'find':

test/functional/spec/crud/read/count-collation.json

@@ -8,7 +8,25 @@
   "minServerVersion": "3.4",
   "tests": [
     {
-      "description": "Count with collation",
+      "description": "Count documents with collation",
+      "operation": {
+        "name": "countDocuments",
+        "arguments": {
+          "filter": {
+            "x": "ping"
+          },
+          "collation": {
+            "locale": "en_US",
+            "strength": 2
+          }
+        }
+      },
+      "outcome": {
+        "result": 1
+      }
+    },
+    {
+      "description": "Deprecated count with collation",
       "operation": {
         "name": "count",
         "arguments": {

test/functional/spec/crud/read/count-collation.yml

@@ -4,12 +4,22 @@ minServerVersion: '3.4'
 
 tests:
     -
-        description: "Count with collation"
+        description: "Count documents with collation"
         operation:
-            name: count
+            name: countDocuments
             arguments:
                 filter: { x: 'ping' }
                 collation: { locale: 'en_US', strength: 2 } # https://docs.mongodb.com/master/reference/collation/#collation-document
 
         outcome:
             result: 1
+    -
+        description: "Deprecated count with collation"
+        operation:
+            name: count
+            arguments:
+                filter: { x: 'ping' }
+                collation: { locale: 'en_US', strength: 2 }
+
+        outcome:
+            result: 1

test/functional/spec/crud/read/count.json

@@ -15,7 +15,59 @@
   ],
   "tests": [
     {
-      "description": "Count without a filter",
+      "description": "Estimated document count",
+      "operation": {
+        "name": "estimatedDocumentCount",
+        "arguments": {}
+      },
+      "outcome": {
+        "result": 3
+      }
+    },
+    {
+      "description": "Count documents without a filter",
+      "operation": {
+        "name": "countDocuments",
+        "arguments": {
+          "filter": {}
+        }
+      },
+      "outcome": {
+        "result": 3
+      }
+    },
+    {
+      "description": "Count documents with a filter",
+      "operation": {
+        "name": "countDocuments",
+        "arguments": {
+          "filter": {
+            "_id": {
+              "$gt": 1
+            }
+          }
+        }
+      },
+      "outcome": {
+        "result": 2
+      }
+    },
+    {
+      "description": "Count documents with skip and limit",
+      "operation": {
+        "name": "countDocuments",
+        "arguments": {
+          "filter": {},
+          "skip": 1,
+          "limit": 3
+        }
+      },
+      "outcome": {
+        "result": 2
+      }
+    },
+    {
+      "description": "Deprecated count without a filter",
       "operation": {
         "name": "count",
         "arguments": {
@@ -27,7 +79,7 @@
       }
     },
     {
-      "description": "Count with a filter",
+      "description": "Deprecated count with a filter",
       "operation": {
         "name": "count",
         "arguments": {
@@ -43,9 +95,9 @@
       }
     },
     {
-      "description": "Count with skip and limit",
+      "description": "Deprecated count with skip and limit",
       "operation": {
-        "name": "count",
+        "name": "countDocuments",
         "arguments": {
           "filter": {},
           "skip": 1,