detect postgres version for saved datasources

public/app/plugins/datasource/postgres/config_ctrl.ts

+import _ from 'lodash';
+
+export class PostgresConfigCtrl {
+  static templateUrl = 'partials/config.html';
+
+  current: any;
+  datasourceSrv: any;
+
+  /** @ngInject **/
+  constructor($scope, datasourceSrv) {
+    this.datasourceSrv = datasourceSrv;
+    this.current.jsonData.sslmode = this.current.jsonData.sslmode || 'verify-full';
+    this.current.jsonData.postgresVersion = this.current.jsonData.postgresVersion || 903;
+    this.autoDetectPostgresVersion();
+  }
+
+  autoDetectPostgresVersion() {
+    if (!this.current.id) {
+      return;
+    }
+
+    this.datasourceSrv
+      .loadDatasource(this.current.name)
+      .then(ds => {
+        return ds.getVersion();
+      })
+      .then(version => {
+        version = Number(version[0].text);
+        let major = Math.trunc(version / 100);
+        let minor = version % 100;
+        let name = String(major);
+        if (version < 1000) {
+          name = String(major) + '.' + String(minor);
+        }
+        if (!_.find(this.postgresVersions, (p: any) => p.value === version)) {
+          this.postgresVersions.push({ name: name, value: version });
+        }
+        this.current.jsonData.postgresVersion = version;
+      });
+  }
+
+  // the value portion is derived from postgres server_version_num/100
+  postgresVersions = [
+    { name: '9.3', value: 903 },
+    { name: '9.4', value: 904 },
+    { name: '9.5', value: 905 },
+    { name: '9.6', value: 906 },
+    { name: '10', value: 1000 },
+  ];
+}

public/app/plugins/datasource/postgres/datasource.ts

@@ -124,6 +124,10 @@ export class PostgresDatasource {
       .then(data => this.responseParser.parseMetricFindQueryResult(refId, data));
   }
 
+  getVersion() {
+    return this.metricFindQuery("SELECT current_setting('server_version_num')::int/100", {});
+  }
+
   testDatasource() {
     return this.metricFindQuery('SELECT 1', {})
       .then(res => {

public/app/plugins/datasource/postgres/module.ts

 import { PostgresDatasource } from './datasource';
 import { PostgresQueryCtrl } from './query_ctrl';
-
-class PostgresConfigCtrl {
-  static templateUrl = 'partials/config.html';
-
-  current: any;
-
-  /** @ngInject **/
-  constructor($scope) {
-    this.current.jsonData.sslmode = this.current.jsonData.sslmode || 'verify-full';
-  }
-
-  // the value portion is derived from postgres server_version_num/100
-  postgresVersions = [
-    { name: '9.3.x', value: 903 },
-    { name: '9.4.x', value: 904 },
-    { name: '9.5.x', value: 905 },
-    { name: '9.6.x', value: 906 },
-  ];
-}
+import { PostgresConfigCtrl } from './config_ctrl';
 
 const defaultQuery = `SELECT
   extract(epoch from time_column) AS time,