Allow updating dataset types

src/core/core.controller.js

@@ -289,9 +289,13 @@ module.exports = function(Chart) {
 
 			helpers.each(me.data.datasets, function(dataset, datasetIndex) {
 				var meta = me.getDatasetMeta(datasetIndex);
-				if (!meta.type) {
-					meta.type = dataset.type || me.config.type;
+				var type = dataset.type || me.config.type;
+
+				if (meta.type && meta.type !== type) {
+					me.destroyDatasetMeta(datasetIndex);
+					meta = me.getDatasetMeta(datasetIndex);
 				}
+				meta.type = type;
 
 				types.push(meta.type);
 
@@ -672,20 +676,30 @@ module.exports = function(Chart) {
 			return this.options.legendCallback(this);
 		},
 
+		/**
+		 * @private
+		 */
+		destroyDatasetMeta: function(datasetIndex) {
+			var id = this.id;
+			var dataset = this.data.datasets[datasetIndex];
+			var meta = dataset._meta && dataset._meta[id];
+
+			if (meta) {
+				meta.controller.destroy();
+				delete dataset._meta[id];
+			}
+		},
+
 		destroy: function() {
 			var me = this;
 			var canvas = me.canvas;
-			var meta, i, ilen;
+			var i, ilen;
 
 			me.stop();
 
 			// dataset controllers need to cleanup associated data
 			for (i = 0, ilen = me.data.datasets.length; i < ilen; ++i) {
-				meta = me.getDatasetMeta(i);
-				if (meta.controller) {
-					meta.controller.destroy();
-					meta.controller = null;
-				}
+				me.destroyDatasetMeta(i);
 			}
 
 			if (canvas) {

test/specs/core.controller.tests.js

@@ -693,6 +693,41 @@ describe('Chart', function() {
 			chart.update();
 			expect(chart.tooltip._options).toEqual(jasmine.objectContaining(newTooltipConfig));
 		});
+
+		it ('should update the metadata', function() {
+			var cfg = {
+				data: {
+					labels: ['A', 'B', 'C', 'D'],
+					datasets: [{
+						type: 'line',
+						data: [10, 20, 30, 0]
+					}]
+				},
+				options: {
+					responsive: true,
+					scales: {
+						xAxes: [{
+							type: 'time'
+						}],
+						yAxes: [{
+							scaleLabel: {
+								display: true,
+								labelString: 'Value'
+							}
+						}]
+					}
+				}
+			};
+			var chart = acquireChart(cfg);
+			var meta = chart.getDatasetMeta(0);
+			expect(meta.type).toBe('line');
+
+			// change the dataset to bar and check that meta was updated
+			chart.config.data.datasets[0].type = 'bar';
+			chart.update();
+			meta = chart.getDatasetMeta(0);
+			expect(meta.type).toBe('bar');
+		});
 	});
 
 	describe('plugin.extensions', function() {