Reduce usage of EPM SO. Add getInstallation().

Replaced two calls of getInstallationObject() with getInstallation().

Two less places with knowledge of SO internals.

Lots of potential improvements for EPM TS types remain (refactoring/removing Installable, etc), but this is a good incremental step, IMO

x-pack/legacy/plugins/epm/server/packages/get.ts

@@ -81,6 +81,14 @@ export async function getInstallationObject(options: {
     .catch(e => undefined);
 }
 
+export async function getInstallation(options: {
+  savedObjectsClient: SavedObjectsClientContract;
+  pkgkey: string;
+}) {
+  const savedObject = await getInstallationObject(options);
+  return savedObject?.attributes;
+}
+
 function sortByName(a: { name: string }, b: { name: string }) {
   if (a.name > b.name) {
     return 1;

x-pack/legacy/plugins/epm/server/packages/install.ts

@@ -10,7 +10,7 @@ import { AssetReference, Installation, KibanaAssetType } from '../../common/type
 import { installIndexPattern } from '../lib/kibana/index_pattern/install';
 import * as Registry from '../registry';
 import { getObject } from './get_objects';
-import { getInstallationObject } from './index';
+import { getInstallation } from './index';
 
 export async function installPackage(options: {
   savedObjectsClient: SavedObjectsClientContract;
@@ -64,15 +64,15 @@ export async function saveInstallationReferences(options: {
   toSave: AssetReference[];
 }) {
   const { savedObjectsClient, pkgkey, toSave } = options;
-  const savedObject = await getInstallationObject({ savedObjectsClient, pkgkey });
-  const savedRefs = savedObject && savedObject.attributes.installed;
+  const installation = await getInstallation({ savedObjectsClient, pkgkey });
+  const savedRefs = installation?.installed || [];
   const mergeRefsReducer = (current: AssetReference[], pending: AssetReference) => {
     const hasRef = current.find(c => c.id === pending.id && c.type === pending.type);
     if (!hasRef) current.push(pending);
     return current;
   };
 
-  const toInstall = toSave.reduce(mergeRefsReducer, savedRefs || []);
+  const toInstall = toSave.reduce(mergeRefsReducer, savedRefs);
 
   await savedObjectsClient.create<Installation>(
     SAVED_OBJECT_TYPE_PACKAGES,

x-pack/legacy/plugins/epm/server/packages/remove.ts

@@ -8,16 +8,16 @@ import { SavedObjectsClientContract } from 'src/core/server/';
 import { SAVED_OBJECT_TYPE_PACKAGES } from '../../common/constants';
 import { AssetReference, AssetType, ElasticsearchAssetType } from '../../common/types';
 import { CallESAsCurrentUser } from '../lib/cluster_access';
-import { getInstallationObject, savedObjectTypes } from './index';
+import { getInstallation, savedObjectTypes } from './index';
 
 export async function removeInstallation(options: {
   savedObjectsClient: SavedObjectsClientContract;
   pkgkey: string;
   callCluster: CallESAsCurrentUser;
 }): Promise<AssetReference[]> {
   const { savedObjectsClient, pkgkey, callCluster } = options;
-  const installation = await getInstallationObject({ savedObjectsClient, pkgkey });
-  const installedObjects = (installation && installation.attributes.installed) || [];
+  const installation = await getInstallation({ savedObjectsClient, pkgkey });
+  const installedObjects = installation?.installed || [];
 
   // Delete the manager saved object with references to the asset objects
   // could also update with [] or some other state