feat(fields/filter): add in filter type

Also updated README.md.

README.md

@@ -481,7 +481,7 @@ Create filter spec.
 
 __Arguments__
 
-* type `string | object` - Filter type: `and`, `javascript`, `not`, `or`, `regex`, `selector`, `search` - or raw filter object.
+* type `string | object` - Filter type: `and`, `javascript`, `not`, `or`, `regex`, `selector`, `search`, `in` - or raw filter object.
 * args `...*` - Filter-specific arguments. Described below.
 
 __Query.filter('and', filters...)__
@@ -518,6 +518,13 @@ __Query.filter('search', dimension, query)__
 
 ---
 
+__Query.filter('in', dimension, values)__
+
+* dimensions `string` - Dimension to which filter is applied.
+* values `object[]` - Values to match.
+
+---
+
 #### `static` `object` having(type, [args...])
 
 Create `having` spec.

lib/fields/filters/in.js

@@ -0,0 +1,26 @@
+'use strict'
+
+var FieldError = require('../../errors').FieldError
+
+
+/**
+ * In filter
+ *
+ * @see http://druid.io/docs/0.6.120/Filters.html
+ *
+ * @param {string} dimension Dimension to which filter is applied
+ * @param {*} values Values to match
+ */
+module.exports = function(dimension, values) {
+  if (!dimension || typeof values === 'undefined') {
+    throw new FieldError('Dimension or value is not specified')
+  }
+
+  // convert to empty string, null/empty string are the same thing to druid
+  if (values === null) {
+    values = []
+  }
+
+  this.dimension = dimension
+  this.values = values
+}

spec/fields/filters.js

@@ -245,4 +245,28 @@ describe('Filters', function() {
       }).to.throwException()
     })
   })
+
+  describe('In', function() {
+    it('should create filter', function() {
+      var spec = Query.filter('in', 'dim', ['value1', 'value2'])
+
+      expect(spec).to.eql({
+        type:      'in',
+        dimension: 'dim',
+        values:    ['value1', 'value2']
+      })
+    })
+
+    it('should throw error if dimension is not specified', function() {
+      expect(function() {
+        Query.filter('in', null, 'value')
+      }).to.throwException()
+    })
+
+    it('should throw error if value is not specified', function() {
+      expect(function() {
+        Query.filter('in', 'dimension')
+      }).to.throwException()
+    })
+  })
 })