diff --git a/client/src/components/windows/login/LoginWindow.tsx b/client/src/components/windows/login/LoginWindow.tsx
index 134248a..fe9e216 100644
--- a/client/src/components/windows/login/LoginWindow.tsx
+++ b/client/src/components/windows/login/LoginWindow.tsx
@@ -3,14 +3,23 @@ import { WindowState } from "../Windows";
 import { Box, Paper, Typography, TextField, Button } from "@material-ui/core";
 import { useHistory, useLocation } from 'react-router';
 import { useAuth, Auth } from '../../../lib/useAuth';
+import Alert from '@material-ui/lab/Alert';
+
+export enum LoginStatus {
+    NoneSubmitted = 0,
+    Unsuccessful,
+    // Note: no "successful" status because that would lead to a redirect.
+}
 
 export interface LoginWindowState extends WindowState {
     email: string,
     password: string,
+    status: LoginStatus,
 }
 export enum LoginWindowStateActions {
     SetEmail = "SetEmail",
     SetPassword = "SetPassword",
+    SetStatus = "SetStatus",
 }
 export function LoginWindowReducer(state: LoginWindowState, action: any) {
     switch (action.type) {
@@ -18,6 +27,8 @@ export function LoginWindowReducer(state: LoginWindowState, action: any) {
             return { ...state, email: action.value }
         case LoginWindowStateActions.SetPassword:
             return { ...state, password: action.value }
+        case LoginWindowStateActions.SetStatus:
+            return { ...state, status: action.value }
         default:
             throw new Error("Unimplemented LoginWindow state update.")
     }
@@ -27,6 +38,7 @@ export default function LoginWindow(props: {}) {
     const [state, dispatch] = useReducer(LoginWindowReducer, {
         email: "",
         password: "",
+        status: LoginStatus.NoneSubmitted,
     });
 
     return <LoginWindowControlled state={state} dispatch={dispatch} />
@@ -46,6 +58,11 @@ export function LoginWindowControlled(props: {
         auth.signin(props.state.email, props.state.password)
             .then(() => {
                 history.replace(from);
+            }).catch((e: any) => {
+                props.dispatch({
+                    type: LoginWindowStateActions.SetStatus,
+                    value: LoginStatus.Unsuccessful,
+                })
             })
     }
 
@@ -86,6 +103,10 @@ export function LoginWindowControlled(props: {
                                 value: e.target.value
                             })}
                         />
+                        {props.state.status === LoginStatus.Unsuccessful && <Alert severity="error">
+                            Login failed - Please check your credentials.
+                            </Alert>
+                        }
                         <Button
                             type="submit"
                             fullWidth
diff --git a/server/app.ts b/server/app.ts
index 5a34d00..2411cb3 100644
--- a/server/app.ts
+++ b/server/app.ts
@@ -76,7 +76,7 @@ const SetupApp = (app: any, knex: Knex, apiBaseUrl: string) => {
         })();
     });
 
-    app.use(require('express-session')({ secret: 'keyboard cat', resave: false, saveUninitialized: false }));
+    app.use(require('express-session')({ secret: 'EA9q5cukt7UFhN', resave: false, saveUninitialized: false }));
     app.use(passport.initialize());
     app.use(passport.session());
 
diff --git a/server/endpoints/AlbumDetails.ts b/server/endpoints/AlbumDetails.ts
index e833ff9..6210803 100644
--- a/server/endpoints/AlbumDetails.ts
+++ b/server/endpoints/AlbumDetails.ts
@@ -12,6 +12,8 @@ export const AlbumDetailsEndpointHandler: EndpointHandler = async (req: any, res
         throw e;
     }
 
+    const { id: userId } = req.user;
+
     try {
         // Start transfers for songs, tags and artists.
         // Also request the album itself.
@@ -35,6 +37,7 @@ export const AlbumDetailsEndpointHandler: EndpointHandler = async (req: any, res
             });
         const albumPromise = knex.select('name', 'storeLinks')
             .from('albums')
+            .where({ 'user': userId })
             .where({ id: req.params.id })
             .then((albums: any) => albums[0]);
 
@@ -43,7 +46,6 @@ export const AlbumDetailsEndpointHandler: EndpointHandler = async (req: any, res
             await Promise.all([albumPromise, tagIdsPromise, songIdsPromise, artistIdsPromise]);
 
         // Respond to the request.
-        console.log("ALBUM: ", album);
         const response: api.AlbumDetailsResponse = {
             name: album['name'],
             artistIds: artists,
diff --git a/server/endpoints/ArtistDetails.ts b/server/endpoints/ArtistDetails.ts
index ede0836..76f42ff 100644
--- a/server/endpoints/ArtistDetails.ts
+++ b/server/endpoints/ArtistDetails.ts
@@ -12,6 +12,8 @@ export const ArtistDetailsEndpointHandler: EndpointHandler = async (req: any, re
         throw e;
     }
 
+    const { id: userId } = req.user;
+
     try {
         const tagIds = Array.from(new Set((await knex.select('tagId')
             .from('artists_tags')
@@ -20,6 +22,7 @@ export const ArtistDetailsEndpointHandler: EndpointHandler = async (req: any, re
 
         const results = await knex.select(['id', 'name', 'storeLinks'])
             .from('artists')
+            .where({ 'user': userId })
             .where({ 'id': req.params.id });
 
         const response: api.ArtistDetailsResponse = {
diff --git a/server/endpoints/CreateAlbum.ts b/server/endpoints/CreateAlbum.ts
index e9f9509..7172d5b 100644
--- a/server/endpoints/CreateAlbum.ts
+++ b/server/endpoints/CreateAlbum.ts
@@ -11,8 +11,9 @@ export const CreateAlbumEndpointHandler: EndpointHandler = async (req: any, res:
     throw e;
   }
   const reqObject: api.CreateAlbumRequest = req.body;
+  const { id: userId } = req.user;
 
-  console.log("Create Album:", reqObject);
+  console.log("User ", userId, ": Create Album ", reqObject);
 
   await knex.transaction(async (trx) => {
     try {
@@ -20,6 +21,7 @@ export const CreateAlbumEndpointHandler: EndpointHandler = async (req: any, res:
       const artistIdsPromise = reqObject.artistIds ?
         trx.select('id')
           .from('artists')
+          .where({ 'user': userId })
           .whereIn('id', reqObject.artistIds)
           .then((as: any) => as.map((a: any) => a['id'])) :
         (async () => { return [] })();
@@ -28,6 +30,7 @@ export const CreateAlbumEndpointHandler: EndpointHandler = async (req: any, res:
       const tagIdsPromise = reqObject.tagIds ?
         trx.select('id')
           .from('tags')
+          .where({ 'user': userId })
           .whereIn('id', reqObject.tagIds)
           .then((as: any) => as.map((a: any) => a['id'])) :
         (async () => { return [] })();
@@ -50,6 +53,7 @@ export const CreateAlbumEndpointHandler: EndpointHandler = async (req: any, res:
         .insert({
           name: reqObject.name,
           storeLinks: JSON.stringify(reqObject.storeLinks || []),
+          user: userId,
         })
         .returning('id') // Needed for Postgres
       )[0];
diff --git a/server/endpoints/CreateArtist.ts b/server/endpoints/CreateArtist.ts
index 155e9d2..0496c47 100644
--- a/server/endpoints/CreateArtist.ts
+++ b/server/endpoints/CreateArtist.ts
@@ -11,8 +11,9 @@ export const CreateArtistEndpointHandler: EndpointHandler = async (req: any, res
         throw e;
     }
     const reqObject: api.CreateArtistRequest = req.body;
+    const { id: userId } = req.user;
 
-    console.log("Create artist:", reqObject)
+    console.log("User ", userId, ": Create artist ", reqObject)
 
     await knex.transaction(async (trx) => {
         try {
@@ -20,13 +21,12 @@ export const CreateArtistEndpointHandler: EndpointHandler = async (req: any, res
             const tags: number[] = reqObject.tagIds ?
                 Array.from(new Set(
                     (await trx.select('id').from('tags')
+                        .where({ 'user': userId })
                         .whereIn('id', reqObject.tagIds))
                         .map((tag: any) => tag['id'])
                 ))
                 : [];
 
-            console.log("Found artist tags:", tags)
-
             if (reqObject.tagIds && tags && tags.length !== reqObject.tagIds.length) {
                 const e: EndpointError = {
                     internalMessage: 'Not all tags exist for CreateArtist request: ' + JSON.stringify(req.body),
@@ -40,6 +40,7 @@ export const CreateArtistEndpointHandler: EndpointHandler = async (req: any, res
                 .insert({
                     name: reqObject.name,
                     storeLinks: JSON.stringify(reqObject.storeLinks || []),
+                    user: userId,
                 })
                 .returning('id') // Needed for Postgres
             )[0];
diff --git a/server/endpoints/CreateSong.ts b/server/endpoints/CreateSong.ts
index 89fdf58..a3c80c1 100644
--- a/server/endpoints/CreateSong.ts
+++ b/server/endpoints/CreateSong.ts
@@ -11,8 +11,9 @@ export const CreateSongEndpointHandler: EndpointHandler = async (req: any, res:
     throw e;
   }
   const reqObject: api.CreateSongRequest = req.body;
+  const { id: userId } = req.user;
 
-  console.log("Create Song:", reqObject);
+  console.log("User ", userId, ": Create Song ", reqObject);
 
   await knex.transaction(async (trx) => {
     try {
@@ -20,6 +21,7 @@ export const CreateSongEndpointHandler: EndpointHandler = async (req: any, res:
       const artistIdsPromise = reqObject.artistIds ?
         trx.select('id')
           .from('artists')
+          .where({ 'user': userId })
           .whereIn('id', reqObject.artistIds)
           .then((as: any) => as.map((a: any) => a['id'])) :
         (async () => { return [] })();
@@ -28,6 +30,7 @@ export const CreateSongEndpointHandler: EndpointHandler = async (req: any, res:
       const tagIdsPromise = reqObject.tagIds ?
         trx.select('id')
           .from('tags')
+          .where({ 'user': userId })
           .whereIn('id', reqObject.tagIds)
           .then((as: any) => as.map((a: any) => a['id'])) :
         (async () => { return [] })();
@@ -36,6 +39,7 @@ export const CreateSongEndpointHandler: EndpointHandler = async (req: any, res:
       const albumIdsPromise = reqObject.albumIds ?
         trx.select('id')
           .from('albums')
+          .where({ 'user': userId })
           .whereIn('id', reqObject.albumIds)
           .then((as: any) => as.map((a: any) => a['id'])) :
         (async () => { return [] })();
@@ -59,6 +63,7 @@ export const CreateSongEndpointHandler: EndpointHandler = async (req: any, res:
         .insert({
           title: reqObject.title,
           storeLinks: JSON.stringify(reqObject.storeLinks || []),
+          user: userId,
         })
         .returning('id') // Needed for Postgres
       )[0];
diff --git a/server/endpoints/CreateTag.ts b/server/endpoints/CreateTag.ts
index 183ed1c..1587bcf 100644
--- a/server/endpoints/CreateTag.ts
+++ b/server/endpoints/CreateTag.ts
@@ -11,8 +11,9 @@ export const CreateTagEndpointHandler: EndpointHandler = async (req: any, res: a
         throw e;
     }
     const reqObject: api.CreateTagRequest = req.body;
+    const { id: userId } = req.user;
 
-    console.log("Create Tag: ", reqObject);
+    console.log("User ", userId, ": Create Tag ", reqObject);
 
     await knex.transaction(async (trx) => {
         try {
@@ -21,6 +22,7 @@ export const CreateTagEndpointHandler: EndpointHandler = async (req: any, res: a
                 reqObject.parentId ?
                     (await trx.select('id')
                         .from('tags')
+                        .where({ 'user': userId })
                         .where({ 'id': reqObject.parentId }))[0]['id'] :
                     undefined;
 
@@ -35,7 +37,8 @@ export const CreateTagEndpointHandler: EndpointHandler = async (req: any, res: a
 
             // Create the new tag.
             var tag: any = {
-                name: reqObject.name
+                name: reqObject.name,
+                user: userId,
             };
             if (maybeParent) {
                 tag['parentId'] = maybeParent;
diff --git a/server/endpoints/DeleteTag.ts b/server/endpoints/DeleteTag.ts
index 6d0ab94..3fd9ae3 100644
--- a/server/endpoints/DeleteTag.ts
+++ b/server/endpoints/DeleteTag.ts
@@ -2,13 +2,14 @@ import * as api from '../../client/src/api';
 import { EndpointError, EndpointHandler, catchUnhandledErrors } from './types';
 import Knex from 'knex';
 
-async function getChildrenRecursive(id: number, trx: any) {
+async function getChildrenRecursive(id: number, userId: number, trx: any) {
     const directChildren = (await trx.select('id')
         .from('tags')
+        .where({ 'user': userId })
         .where({ 'parentId': id })).map((r: any) => r.id);
 
     const indirectChildrenPromises = directChildren.map(
-        (child: number) => getChildrenRecursive(child, trx)
+        (child: number) => getChildrenRecursive(child, userId, trx)
     );
     const indirectChildrenNested = await Promise.all(indirectChildrenPromises);
     const indirectChildren = indirectChildrenNested.flat();
@@ -28,19 +29,20 @@ export const DeleteTagEndpointHandler: EndpointHandler = async (req: any, res: a
         throw e;
     }
     const reqObject: api.DeleteTagRequest = req.body;
+    const { id: userId } = req.user;
 
-    console.log("Delete Tag:", reqObject);
+    console.log("User ", userId, ": Delete Tag ", reqObject);
 
     await knex.transaction(async (trx) => {
         try {
             // Start retrieving any child tags.
-
             const childTagsPromise = 
-                getChildrenRecursive(req.params.id, trx);
+                getChildrenRecursive(req.params.id, userId, trx);
 
             // Start retrieving the tag itself.
             const tagPromise = trx.select('id')
                 .from('tags')
+                .where({ 'user': userId })
                 .where({ id: req.params.id })
                 .then((r: any) => (r && r[0]) ? r[0]['id'] : undefined)
 
@@ -49,7 +51,6 @@ export const DeleteTagEndpointHandler: EndpointHandler = async (req: any, res: a
 
             // Merge all IDs.
             const toDelete = [ tag, ...children ];
-            console.log ("deleting tags: ", toDelete);
 
             // Check that we found all objects we need.
             if (!tag) {
@@ -62,6 +63,7 @@ export const DeleteTagEndpointHandler: EndpointHandler = async (req: any, res: a
 
             // Delete the tag and its children.
             await trx('tags')
+                .where({ 'user': userId })
                 .whereIn('id', toDelete)
                 .del();
 
diff --git a/server/endpoints/MergeTag.ts b/server/endpoints/MergeTag.ts
index b84db4b..ed776c5 100644
--- a/server/endpoints/MergeTag.ts
+++ b/server/endpoints/MergeTag.ts
@@ -11,8 +11,9 @@ export const MergeTagEndpointHandler: EndpointHandler = async (req: any, res: an
         throw e;
     }
     const reqObject: api.DeleteTagRequest = req.body;
+    const { id: userId } = req.user;
 
-    console.log("Merge Tag:", reqObject);
+    console.log("User ", userId, ": Merge Tag ", reqObject);
     const fromId = req.params.id;
     const toId = req.params.toId;
 
@@ -21,12 +22,14 @@ export const MergeTagEndpointHandler: EndpointHandler = async (req: any, res: an
             // Start retrieving the "from" tag.
             const fromTagPromise = trx.select('id')
                 .from('tags')
+                .where({ 'user': userId })
                 .where({ id: fromId })
                 .then((r: any) => (r && r[0]) ? r[0]['id'] : undefined)
 
             // Start retrieving the "to" tag.
             const toTagPromise = trx.select('id')
                 .from('tags')
+                .where({ 'user': userId })
                 .where({ id: toId })
                 .then((r: any) => (r && r[0]) ? r[0]['id'] : undefined)
 
@@ -44,6 +47,7 @@ export const MergeTagEndpointHandler: EndpointHandler = async (req: any, res: an
 
             // Assign new tag ID to any objects referencing the to-be-merged tag.
             const cPromise = trx('tags')
+                .where({ 'user': userId })
                 .where({ 'parentId': fromId })
                 .update({ 'parentId': toId });
             const sPromise = trx('songs_tags')
@@ -59,6 +63,7 @@ export const MergeTagEndpointHandler: EndpointHandler = async (req: any, res: an
 
             // Delete the original tag.
             await trx('tags')
+                .where({ 'user': userId })
                 .where({ 'id': fromId })
                 .del();
 
diff --git a/server/endpoints/ModifyAlbum.ts b/server/endpoints/ModifyAlbum.ts
index 8d01eb0..829f6c2 100644
--- a/server/endpoints/ModifyAlbum.ts
+++ b/server/endpoints/ModifyAlbum.ts
@@ -11,8 +11,9 @@ export const ModifyAlbumEndpointHandler: EndpointHandler = async (req: any, res:
         throw e;
     }
     const reqObject: api.ModifyAlbumRequest = req.body;
+    const { id: userId } = req.user;
 
-    console.log("Modify Album:", reqObject);
+    console.log("User ", userId, ": Modify Album ", reqObject);
 
     await knex.transaction(async (trx) => {
         try {
@@ -20,6 +21,7 @@ export const ModifyAlbumEndpointHandler: EndpointHandler = async (req: any, res:
             // Start retrieving the album itself.
             const albumPromise = trx.select('id')
                 .from('albums')
+                .where({ 'user': userId })
                 .where({ id: req.params.id })
                 .then((r: any) => (r && r[0]) ? r[0]['id'] : undefined);
 
@@ -58,6 +60,7 @@ export const ModifyAlbumEndpointHandler: EndpointHandler = async (req: any, res:
             if ("name" in reqObject) { update["name"] = reqObject.name; }
             if ("storeLinks" in reqObject) { update["storeLinks"] = JSON.stringify(reqObject.storeLinks || []); }
             const modifyAlbumPromise = trx('albums')
+                .where({ 'user': userId })
                 .where({ 'id': req.params.id })
                 .update(update)
 
diff --git a/server/endpoints/ModifyArtist.ts b/server/endpoints/ModifyArtist.ts
index b0cc77e..3d56ee6 100644
--- a/server/endpoints/ModifyArtist.ts
+++ b/server/endpoints/ModifyArtist.ts
@@ -11,7 +11,9 @@ export const ModifyArtistEndpointHandler: EndpointHandler = async (req: any, res
         throw e;
     }
     const reqObject: api.ModifyArtistRequest = req.body;
-    console.log("Modify Artist:", reqObject);
+    const { id: userId } = req.user;
+
+    console.log("User ", userId, ": Modify Artist ", reqObject);
 
     await knex.transaction(async (trx) => {
         try {
@@ -20,6 +22,7 @@ export const ModifyArtistEndpointHandler: EndpointHandler = async (req: any, res
             // Start retrieving the artist itself.
             const artistPromise = trx.select('id')
                 .from('artists')
+                .where({ 'user': userId })
                 .where({ id: artistId })
                 .then((r: any) => (r && r[0]) ? r[0]['id'] : undefined)
 
@@ -49,6 +52,7 @@ export const ModifyArtistEndpointHandler: EndpointHandler = async (req: any, res
             if ("name" in reqObject) { update["name"] = reqObject.name; }
             if ("storeLinks" in reqObject) { update["storeLinks"] = JSON.stringify(reqObject.storeLinks || []); }
             const modifyArtistPromise = trx('artists')
+                .where({ 'user': userId })
                 .where({ 'id': artistId })
                 .update(update)
 
diff --git a/server/endpoints/ModifySong.ts b/server/endpoints/ModifySong.ts
index 9a280f4..488b72f 100644
--- a/server/endpoints/ModifySong.ts
+++ b/server/endpoints/ModifySong.ts
@@ -11,14 +11,16 @@ export const ModifySongEndpointHandler: EndpointHandler = async (req: any, res:
         throw e;
     }
     const reqObject: api.ModifySongRequest = req.body;
+    const { id: userId } = req.user;
 
-    console.log("Modify Song:", reqObject);
+    console.log("User ", userId, ": Modify Song ", reqObject);
 
     await knex.transaction(async (trx) => {
         try {
             // Retrieve the song to be modified itself.
             const songPromise = trx.select('id')
                 .from('songs')
+                .where({ 'user': userId })
                 .where({ id: req.params.id })
                 .then((r: any) => (r && r[0]) ? r[0]['id'] : undefined)
 
@@ -67,6 +69,7 @@ export const ModifySongEndpointHandler: EndpointHandler = async (req: any, res:
             if ("title" in reqObject) { update["title"] = reqObject.title; }
             if ("storeLinks" in reqObject) { update["storeLinks"] = JSON.stringify(reqObject.storeLinks || []); }
             const modifySongPromise = trx('songs')
+                .where({ 'user': userId })
                 .where({ 'id': req.params.id })
                 .update(update)
 
diff --git a/server/endpoints/ModifyTag.ts b/server/endpoints/ModifyTag.ts
index adfb558..6596958 100644
--- a/server/endpoints/ModifyTag.ts
+++ b/server/endpoints/ModifyTag.ts
@@ -11,8 +11,9 @@ export const ModifyTagEndpointHandler: EndpointHandler = async (req: any, res: a
         throw e;
     }
     const reqObject: api.ModifyTagRequest = req.body;
+    const { id: userId } = req.user;
 
-    console.log("Modify Tag:", reqObject);
+    console.log("User ", userId, ": Modify Tag ", reqObject);
 
     await knex.transaction(async (trx) => {
         try {
@@ -20,6 +21,7 @@ export const ModifyTagEndpointHandler: EndpointHandler = async (req: any, res: a
             const parentTagPromise = reqObject.parentId ?
                 trx.select('id')
                     .from('tags')
+                    .where({ 'user': userId })
                     .where({ 'id': reqObject.parentId })
                     .then((ts: any) => ts.map((t: any) => t['tagId'])) :
                 (async () => { return [] })();
@@ -27,6 +29,7 @@ export const ModifyTagEndpointHandler: EndpointHandler = async (req: any, res: a
             // Start retrieving the tag itself.
             const tagPromise = trx.select('id')
                 .from('tags')
+                .where({ 'user': userId })
                 .where({ id: req.params.id })
                 .then((r: any) => (r && r[0]) ? r[0]['id'] : undefined)
 
@@ -45,6 +48,7 @@ export const ModifyTagEndpointHandler: EndpointHandler = async (req: any, res: a
 
             // Modify the tag.
             await trx('tags')
+                .where({ 'user': userId })
                 .where({ 'id': req.params.id })
                 .update({
                     name: reqObject.name,
diff --git a/server/endpoints/Query.ts b/server/endpoints/Query.ts
index 89fb35d..60111f3 100644
--- a/server/endpoints/Query.ts
+++ b/server/endpoints/Query.ts
@@ -178,7 +178,7 @@ const objectColumns = {
     [ObjectType.Tag]: ['tags.id as tags.id', 'tags.name as tags.name', 'tags.parentId as tags.parentId']
 };
 
-function constructQuery(knex: Knex, queryFor: ObjectType, queryElem: api.QueryElem, ordering: api.Ordering,
+function constructQuery(knex: Knex, userId: number, queryFor: ObjectType, queryElem: api.QueryElem, ordering: api.Ordering,
     offset: number, limit: number | null) {
     const joinObjects = getRequiredDatabaseObjects(queryElem);
     joinObjects.delete(queryFor); // We are already querying this object in the base query.
@@ -194,6 +194,7 @@ function constructQuery(knex: Knex, queryFor: ObjectType, queryElem: api.QueryEl
 
     // First, we create a base query for the type of object we need to yield.
     var q = knex.select(columns)
+        .where({ [objectTables[queryFor] + '.user']: userId })
         .groupBy(objectTables[queryFor] + '.' + 'id')
         .from(objectTables[queryFor]);
 
@@ -223,7 +224,7 @@ function constructQuery(knex: Knex, queryFor: ObjectType, queryElem: api.QueryEl
     return q;
 }
 
-async function getLinkedObjects(knex: Knex, base: ObjectType, linked: ObjectType, baseIds: number[]) {
+async function getLinkedObjects(knex: Knex, userId: number, base: ObjectType, linked: ObjectType, baseIds: number[]) {
     var result: Record<number, any[]> = {};
     const otherTable = objectTables[linked];
     const linkingTable = getLinkingTable(base, linked);
@@ -232,6 +233,7 @@ async function getLinkedObjects(knex: Knex, base: ObjectType, linked: ObjectType
     await Promise.all(baseIds.map((baseId: number) => {
         return knex.select(columns).groupBy(otherTable + '.id').from(otherTable)
             .join(linkingTable, { [linkingTable + '.' + linkingTableIdNames[linked]]: otherTable + '.id' })
+            .where({ [otherTable + '.user']: userId })
             .where({ [linkingTable + '.' + linkingTableIdNames[base]]: baseId })
             .then((others: any) => { result[baseId] = others; })
     }))
@@ -241,11 +243,12 @@ async function getLinkedObjects(knex: Knex, base: ObjectType, linked: ObjectType
 }
 
 // Resolve a tag into the full nested structure of its ancestors.
-async function getFullTag(knex: Knex, tag: any): Promise<any> {
+async function getFullTag(knex: Knex, userId: number, tag: any): Promise<any> {
     const resolveTag = async (t: any) => {
         if (t['tags.parentId']) {
             const parent = (await knex.select(objectColumns[ObjectType.Tag])
                 .from('tags')
+                .where({ 'user': userId })
                 .where({ [objectTables[ObjectType.Tag] + '.id']: t['tags.parentId'] }))[0];
             t.parent = await resolveTag(parent);
         }
@@ -264,7 +267,9 @@ export const QueryEndpointHandler: EndpointHandler = async (req: any, res: any,
         throw e;
     }
     const reqObject: api.QueryRequest = req.body;
-    console.log("Query: ", reqObject);
+    const { id: userId } = req.user;
+
+    console.log("User ", userId, ": Query ", reqObject);
 
     try {
         const songLimit = reqObject.offsetsLimits.songLimit;
@@ -278,6 +283,7 @@ export const QueryEndpointHandler: EndpointHandler = async (req: any, res: any,
 
         const artistsPromise: Promise<any> = (artistLimit && artistLimit !== 0) ?
             constructQuery(knex,
+                userId,
                 ObjectType.Artist,
                 reqObject.query,
                 reqObject.ordering,
@@ -288,6 +294,7 @@ export const QueryEndpointHandler: EndpointHandler = async (req: any, res: any,
 
         const albumsPromise: Promise<any> = (albumLimit && albumLimit !== 0) ?
             constructQuery(knex,
+                userId,
                 ObjectType.Album,
                 reqObject.query,
                 reqObject.ordering,
@@ -298,6 +305,7 @@ export const QueryEndpointHandler: EndpointHandler = async (req: any, res: any,
 
         const songsPromise: Promise<any> = (songLimit && songLimit !== 0) ?
             constructQuery(knex,
+                userId,
                 ObjectType.Song,
                 reqObject.query,
                 reqObject.ordering,
@@ -308,6 +316,7 @@ export const QueryEndpointHandler: EndpointHandler = async (req: any, res: any,
 
         const tagsPromise: Promise<any> = (tagLimit && tagLimit !== 0) ?
             constructQuery(knex,
+                userId,
                 ObjectType.Tag,
                 reqObject.query,
                 reqObject.ordering,
@@ -325,18 +334,18 @@ export const QueryEndpointHandler: EndpointHandler = async (req: any, res: any,
         })();
         const songsArtistsPromise: Promise<Record<number, any[]>> = (songLimit && songLimit !== 0) ?
             (async () => {
-                return await getLinkedObjects(knex, ObjectType.Song, ObjectType.Artist, await songIdsPromise);
+                return await getLinkedObjects(knex, userId, ObjectType.Song, ObjectType.Artist, await songIdsPromise);
             })() :
             (async () => { return {}; })();
         const songsTagsPromise: Promise<Record<number, any[]>> = (songLimit && songLimit !== 0) ?
             (async () => {
-                const tagsPerSong: Record<number, any> = await getLinkedObjects(knex, ObjectType.Song, ObjectType.Tag, await songIdsPromise);
+                const tagsPerSong: Record<number, any> = await getLinkedObjects(knex, userId, ObjectType.Song, ObjectType.Tag, await songIdsPromise);
                 var result: Record<number, any> = {};
                 for (var key in tagsPerSong) {
                     const tags = tagsPerSong[key];
                     var fullTags: any[] = [];
                     for (var idx in tags) {
-                        fullTags.push(await getFullTag(knex, tags[idx]));
+                        fullTags.push(await getFullTag(knex, userId, tags[idx]));
                     }
                     result[key] = fullTags;
                 }
@@ -345,7 +354,7 @@ export const QueryEndpointHandler: EndpointHandler = async (req: any, res: any,
             (async () => { return {}; })();
         const songsAlbumsPromise: Promise<Record<number, any[]>> = (songLimit && songLimit !== 0) ?
             (async () => {
-                return await getLinkedObjects(knex, ObjectType.Song, ObjectType.Album, await songIdsPromise);
+                return await getLinkedObjects(knex, userId, ObjectType.Song, ObjectType.Album, await songIdsPromise);
             })() :
             (async () => { return {}; })();
 
diff --git a/server/endpoints/SongDetails.ts b/server/endpoints/SongDetails.ts
index 591e31a..caf13e6 100644
--- a/server/endpoints/SongDetails.ts
+++ b/server/endpoints/SongDetails.ts
@@ -12,6 +12,8 @@ export const SongDetailsEndpointHandler: EndpointHandler = async (req: any, res:
         throw e;
     }
 
+    const { id: userId } = req.user;
+
     try {
         const tagIdsPromise: Promise<number[]> = knex.select('tagId')
             .from('songs_tags')
@@ -41,6 +43,7 @@ export const SongDetailsEndpointHandler: EndpointHandler = async (req: any, res:
             })
         const songPromise = await knex.select(['id', 'title', 'storeLinks'])
             .from('songs')
+            .where({ 'user': userId })
             .where({ 'id': req.params.id })
             .then((ss: any) => ss[0])
 
diff --git a/server/endpoints/TagDetails.ts b/server/endpoints/TagDetails.ts
index 7497acb..8fb119a 100644
--- a/server/endpoints/TagDetails.ts
+++ b/server/endpoints/TagDetails.ts
@@ -11,9 +11,12 @@ export const TagDetailsEndpointHandler: EndpointHandler = async (req: any, res:
         throw e;
     }
 
+    const { id: userId } = req.user;
+
     try {
         const results = await knex.select(['id', 'name', 'parentId'])
             .from('tags')
+            .where({ 'user': userId })
             .where({ 'id': req.params.id });
 
         const response: api.TagDetailsResponse = {
diff --git a/server/migrations/20201110170100_add_users.ts b/server/migrations/20201110170100_add_users.ts
index ec62753..5384bc8 100644
--- a/server/migrations/20201110170100_add_users.ts
+++ b/server/migrations/20201110170100_add_users.ts
@@ -1,4 +1,5 @@
 import * as Knex from "knex";
+import { sha512 } from "js-sha512";
 
 
 export async function up(knex: Knex): Promise<void> {
@@ -11,10 +12,63 @@ export async function up(knex: Knex): Promise<void> {
             table.string('passwordHash')
         }
     )
+
+    // Add user column to other object tables.
+    // FIXME: figure out what happens in practice with pre-existing objects.
+    await knex.schema.alterTable(
+        'songs',
+        (table: any) => {
+            table.integer('user').unsigned().notNullable().defaultTo(1);
+        }
+    )
+    await knex.schema.alterTable(
+        'albums',
+        (table: any) => {
+            table.integer('user').unsigned().notNullable().defaultTo(1);
+        }
+    )
+    await knex.schema.alterTable(
+        'tags',
+        (table: any) => {
+            table.integer('user').unsigned().notNullable().defaultTo(1);
+        }
+    )
+    await knex.schema.alterTable(
+        'artists',
+        (table: any) => {
+            table.integer('user').unsigned().notNullable().defaultTo(1);
+        }
+    )
 }
 
 
 export async function down(knex: Knex): Promise<void> {
     await knex.schema.dropTable('users');
+
+    // Remove the user column
+    await knex.schema.alterTable(
+        'songs',
+        (table: any) => {
+            table.dropColumn('user');
+        }
+    )
+    await knex.schema.alterTable(
+        'albums',
+        (table: any) => {
+            table.dropColumn('user');
+        }
+    )
+    await knex.schema.alterTable(
+        'tags',
+        (table: any) => {
+            table.dropColumn('user');
+        }
+    )
+    await knex.schema.alterTable(
+        'artists',
+        (table: any) => {
+            table.dropColumn('user');
+        }
+    )
 }