Add alternativeCount and skipCount options

Closes #355

README.md

@@ -547,6 +547,24 @@ More options to translate can be found here: https://datatables.net/reference/op
 
 You can set the `titleFn` column option to a function instead of supplying a string `title` option. This is reactively rerun as necessary.
 
+### Optimizing the Total Table Count
+
+By default, a count of the entire available filtered dataset is done on the server. This can be slow for large datasets. You have two options that can help:
+
+First, you can calculate total counts yourself and return them from a function provided as the `alternativeCount` option to your `Tabular.Table`:
+
+```js
+alternativeCount: (selector) => 200,
+```
+
+Second, you can skip the count altogether. If you do this, we return a fake count that ensures the Next button will be available. But the fake count will not be the correct total count, so the paging info and the numbered page buttons will be misleading. To deal with this, you should use `pagingType: 'simple'` and either `info: false` or an `infoCallback` function that omits the total count:
+
+```js
+skipCount: true,
+pagingType: 'simple',
+infoCallback: (settings, start, end) => `Showing ${start} to ${end}`,
+```
+
 ## Integrating DataTables Extensions
 
 There are a wide variety of [useful extensions](http://datatables.net/extensions/index) for DataTables. To integrate them into Tabular, it is best to use the NPM packages.

common/Tabular.js

@@ -30,6 +30,8 @@ Tabular.Table = class {
     this.allowFields = options.allowFields;
     this.changeSelector = options.changeSelector;
     this.throttleRefresh = options.throttleRefresh;
+    this.alternativeCount = options.alternativeCount;
+    this.skipCount = options.skipCount;
 
     if (_.isArray(options.extraFields)) {
       const fields = {};
@@ -41,7 +43,22 @@ Tabular.Table = class {
 
     this.selector = options.selector;
 
-    this.options = _.omit(options, 'collection', 'pub', 'sub', 'onUnload', 'allow', 'allowFields', 'extraFields', 'name', 'selector');
+    this.options = _.omit(
+      options,
+      'collection',
+      'pub',
+      'sub',
+      'onUnload',
+      'allow',
+      'allowFields',
+      'changeSelector',
+      'throttleRefresh',
+      'extraFields',
+      'alternativeCount',
+      'skipCount',
+      'name',
+      'selector'
+    );
 
     Tabular.tablesByName[this.name] = this;
   }

server/main.js

@@ -108,11 +108,22 @@ Meteor.publish('tabular_getInfo', function (tableName, selector, sort, skip, lim
 
   let filteredRecordIds = filteredCursor.map(doc => doc._id);
 
+  // If we are not going to count for real, in order to improve performance, then we will fake
+  // the count to ensure the Next button is always available.
+  const fakeCount = filteredRecordIds.length + skip + 1;
+
   const countCursor = table.collection.find(selector, {fields: {_id: 1}});
 
   let recordReady = false;
   let updateRecords = () => {
-    const currentCount = countCursor.count();
+    let currentCount;
+    if (!table.skipCount) {
+      if (typeof table.alternativeCount === 'function') {
+        currentCount = table.alternativeCount(selector);
+      } else {
+        currentCount = countCursor.count();
+      }
+    }
 
     // From https://datatables.net/manual/server-side
     // recordsTotal: Total records, before filtering (i.e. the total number of records in the database)
@@ -123,8 +134,8 @@ Meteor.publish('tabular_getInfo', function (tableName, selector, sort, skip, lim
       // count() will give us the updated total count
       // every time. It does not take the find options
       // limit into account.
-      recordsTotal: currentCount,
-      recordsFiltered: currentCount
+      recordsTotal: table.skipCount ? fakeCount : currentCount,
+      recordsFiltered: table.skipCount ? fakeCount : currentCount
     };
 
     if (recordReady) {