[BUG] fix median.ts to work for scripted field (#1302) (#1325)

Fix PR comment to replace unused agg to _
remove write function

Issue Resolved: #1296

Signed-off-by: Anan Zhuang <ananzh@amazon.com>
Signed-off-by: Anan <79961084+ananzh@users.noreply.github.com>
(cherry picked from commit 48eec83)

Co-authored-by: Anan <79961084+ananzh@users.noreply.github.com>

src/plugins/data/common/search/aggs/metrics/median.test.ts

@@ -89,4 +89,41 @@ describe('AggTypeMetricMedianProvider class', () => {
       })
     ).toEqual(10);
   });
+
+  it('supports scripted fields', () => {
+    const typesRegistry = mockAggTypesRegistry();
+    const field = {
+      name: 'bytes',
+      scripted: true,
+      language: 'painless',
+      script: 'return 456',
+    };
+    const indexPattern = {
+      id: '1234',
+      title: 'logstash-*',
+      fields: {
+        getByName: () => field,
+        filter: () => [field],
+      },
+    } as any;
+
+    aggConfigs = new AggConfigs(
+      indexPattern,
+      [
+        {
+          id: METRIC_TYPES.MEDIAN,
+          type: METRIC_TYPES.MEDIAN,
+          schema: 'metric',
+          params: {
+            field: 'bytes',
+          },
+        },
+      ],
+      {
+        typesRegistry,
+      }
+    );
+
+    expect(aggConfigs.toDsl()).toMatchSnapshot();
+  });
 });

src/plugins/data/common/search/aggs/metrics/median.ts

@@ -60,10 +60,10 @@ export const getMedianMetricAgg = () => {
         name: 'field',
         type: 'field',
         filterFieldTypes: [OSD_FIELD_TYPES.NUMBER, OSD_FIELD_TYPES.DATE, OSD_FIELD_TYPES.HISTOGRAM],
-        write(agg, output) {
-          output.params.field = agg.getParam('field').name;
-          output.params.percents = [50];
-        },
+      },
+      {
+        name: 'percents',
+        default: [50],
       },
     ],
     getValue(agg, bucket) {