fix(subscriptions): cleanup and simplify fetching subscribers for tasks and projects logic

Vikunja now uses one recursive CTE and a few optimizations to fetch all subscribers for a task or project. This makes the relevant code easier to maintain and more performant.

(cherry picked from commit 4ff8815fe1bfe72e02c10f6a6877c93a630f36a4)

pkg/models/error.go

@@ -1745,7 +1745,7 @@ func IsErrSubscriptionAlreadyExists(err error) bool {
 }
 
 func (err *ErrSubscriptionAlreadyExists) Error() string {
-	return fmt.Sprintf("Subscription for this (entity_id, entity_type, user_id) already exists [EntityType: %d, EntityID: %d, ID: %d]", err.EntityType, err.EntityID, err.UserID)
+	return fmt.Sprintf("Subscription for this (entity_id, entity_type, user_id) already exists [EntityType: %d, EntityID: %d, UserID: %d]", err.EntityType, err.EntityID, err.UserID)
 }
 
 // ErrCodeSubscriptionAlreadyExists holds the unique world-error code of this error
@@ -1760,6 +1760,32 @@ func (err ErrSubscriptionAlreadyExists) HTTPError() web.HTTPError {
 	}
 }
 
+// ErrMustProvideUser represents an error where you need to provide a user to fetch subscriptions
+type ErrMustProvideUser struct {
+}
+
+// IsErrMustProvideUser checks if an error is ErrMustProvideUser.
+func IsErrMustProvideUser(err error) bool {
+	_, ok := err.(*ErrMustProvideUser)
+	return ok
+}
+
+func (err *ErrMustProvideUser) Error() string {
+	return "no user provided while fetching subscriptions"
+}
+
+// ErrCodeMustProvideUser holds the unique world-error code of this error
+const ErrCodeMustProvideUser = 12003
+
+// HTTPError holds the http error description
+func (err ErrMustProvideUser) HTTPError() web.HTTPError {
+	return web.HTTPError{
+		HTTPCode: http.StatusPreconditionFailed,
+		Code:     ErrCodeMustProvideUser,
+		Message:  "You must provide a user to fetch subscriptions",
+	}
+}
+
 // =================
 // Link Share errors
 // =================

pkg/models/listeners.go

@@ -199,7 +199,7 @@ func (s *SendTaskCommentNotification) Handle(msg *message.Message) (err error) {
 		return err
 	}
 
-	subscribers, err := getSubscribersForEntity(sess, SubscriptionEntityTask, event.Task.ID)
+	subscribers, err := GetSubscriptionsForEntity(sess, SubscriptionEntityTask, event.Task.ID)
 	if err != nil {
 		return err
 	}
@@ -279,7 +279,7 @@ func (s *SendTaskAssignedNotification) Handle(msg *message.Message) (err error)
 	sess := db.NewSession()
 	defer sess.Close()
 
-	subscribers, err := getSubscribersForEntity(sess, SubscriptionEntityTask, event.Task.ID)
+	subscribers, err := GetSubscriptionsForEntity(sess, SubscriptionEntityTask, event.Task.ID)
 	if err != nil {
 		return err
 	}
@@ -340,12 +340,12 @@ func (s *SendTaskDeletedNotification) Handle(msg *message.Message) (err error) {
 	sess := db.NewSession()
 	defer sess.Close()
 
-	var subscribers []*Subscription
+	var subscribers []*SubscriptionWithUser
-	subscribers, err = getSubscribersForEntity(sess, SubscriptionEntityTask, event.Task.ID)
+	subscribers, err = GetSubscriptionsForEntity(sess, SubscriptionEntityTask, event.Task.ID)
 	// If the task does not exist and no one has explicitly subscribed to it, we won't find any subscriptions for it.
 	// Hence, we need to check for subscriptions to the parent project manually.
 	if err != nil && (IsErrTaskDoesNotExist(err) || IsErrProjectDoesNotExist(err)) {
-		subscribers, err = getSubscribersForEntity(sess, SubscriptionEntityProject, event.Task.ProjectID)
+		subscribers, err = GetSubscriptionsForEntity(sess, SubscriptionEntityProject, event.Task.ProjectID)
 	}
 	if err != nil {
 		return err
@@ -801,7 +801,7 @@ func (s *SendProjectCreatedNotification) Handle(msg *message.Message) (err error
 	sess := db.NewSession()
 	defer sess.Close()
 
-	subscribers, err := getSubscribersForEntity(sess, SubscriptionEntityProject, event.Project.ID)
+	subscribers, err := GetSubscriptionsForEntity(sess, SubscriptionEntityProject, event.Project.ID)
 	if err != nil {
 		return err
 	}

pkg/models/project.go

@@ -297,10 +297,13 @@ func (p *Project) ReadOne(s *xorm.Session, a web.Auth) (err error) {
 		return
 	}
 
-	p.Subscription, err = GetSubscription(s, SubscriptionEntityProject, p.ID, a)
+	subs, err := GetSubscriptionForUser(s, SubscriptionEntityProject, p.ID, a)
 	if err != nil && IsErrProjectDoesNotExist(err) && isFilter {
 		return nil
 	}
+	if subs != nil {
+		p.Subscription = &subs.Subscription
+	}
 
 	p.Views, err = getViewsForProject(s, p.ID)
 	return
@@ -629,10 +632,23 @@ func addProjectDetails(s *xorm.Session, projects []*Project, a web.Auth) (err er
 		return err
 	}
 
-	subscriptions, err := GetSubscriptionsForProjects(s, projects, a)
+	var subscriptions = make(map[int64][]*Subscription)
+	u, is := a.(*user.User)
+	if is {
+		subscriptionsWithUser, err := GetSubscriptionsForEntitiesAndUser(s, SubscriptionEntityProject, projectIDs, u)
 		if err != nil {
 			log.Errorf("An error occurred while getting project subscriptions for a project: %s", err.Error())
-		subscriptions = make(map[int64][]*Subscription)
+		}
+		if err == nil {
+			for pID, subs := range subscriptionsWithUser {
+				for _, sub := range subs {
+					if _, has := subscriptions[pID]; !has {
+						subscriptions[pID] = []*Subscription{}
+					}
+					subscriptions[pID] = append(subscriptions[pID], &sub.Subscription)
+				}
+			}
+		}
 	}
 
 	views := []*ProjectView{}

pkg/models/subscription.go

@@ -17,12 +17,13 @@
 package models
 
 import (
+	"strconv"
 	"time"
 
-	"xorm.io/builder"
-
 	"code.vikunja.io/api/pkg/user"
+	"code.vikunja.io/api/pkg/utils"
 	"code.vikunja.io/api/pkg/web"
+
 	"xorm.io/xorm"
 )
 
@@ -52,7 +53,6 @@ type Subscription struct {
 	EntityID int64 `xorm:"bigint index not null" json:"entity_id" param:"entityID"`
 
 	// The user who made this subscription
-	User   *user.User `xorm:"-" json:"user"`
 	UserID int64 `xorm:"bigint index not null" json:"-"`
 
 	// A timestamp when this subscription was created. You cannot change this value.
@@ -62,7 +62,18 @@ type Subscription struct {
 	web.Rights   `xorm:"-" json:"-"`
 }
 
-// TableName gives us a better tabel name for the subscriptions table
+type SubscriptionWithUser struct {
+	Subscription `xorm:"extends"`
+	User         *user.User `xorm:"extends" json:"user"`
+}
+
+type subscriptionResolved struct {
+	OriginalEntityID     int64
+	SubscriptionID       int64
+	SubscriptionWithUser `xorm:"extends"`
+}
+
+// TableName gives us a better table name for the subscriptions table
 func (sb *Subscription) TableName() string {
 	return "subscriptions"
 }
@@ -115,28 +126,23 @@ func (et SubscriptionEntityType) validate() error {
 // @Failure 500 {object} models.Message "Internal error"
 // @Router /subscriptions/{entity}/{entityID} [put]
 func (sb *Subscription) Create(s *xorm.Session, auth web.Auth) (err error) {
-	// Rights method alread does the validation of the entity type so we don't need to do that here
+	// Rights method already does the validation of the entity type, so we don't need to do that here
 
 	sb.UserID = auth.GetID()
 
-	sub, err := GetSubscription(s, sb.EntityType, sb.EntityID, auth)
+	sub, err := GetSubscriptionForUser(s, sb.EntityType, sb.EntityID, auth)
 	if err != nil {
 		return err
 	}
 	if sub != nil {
 		return &ErrSubscriptionAlreadyExists{
-			EntityID:   sb.EntityID,
+			EntityID:   sub.EntityID,
-			EntityType: sb.EntityType,
+			EntityType: sub.EntityType,
-			UserID:     sb.UserID,
+			UserID:     sub.UserID,
 		}
 	}
 
 	_, err = s.Insert(sb)
-	if err != nil {
-		return
-	}
-
-	sb.User, err = user.GetFromAuth(auth)
 	return
 }
 
@@ -163,261 +169,228 @@ func (sb *Subscription) Delete(s *xorm.Session, auth web.Auth) (err error) {
 	return
 }
 
-func getSubscriberCondForEntities(entityType SubscriptionEntityType, entityIDs []int64) (cond builder.Cond) {
+func GetSubscriptionForUser(s *xorm.Session, entityType SubscriptionEntityType, entityID int64, a web.Auth) (subscription *SubscriptionWithUser, err error) {
-	if entityType == SubscriptionEntityProject {
-		return builder.And(
-			builder.In("entity_id", entityIDs),
-			builder.Eq{"entity_type": SubscriptionEntityProject},
-		)
-	}
-
-	if entityType == SubscriptionEntityTask {
-		return builder.Or(
-			builder.And(
-				builder.In("entity_id", entityIDs),
-				builder.Eq{"entity_type": SubscriptionEntityTask},
-			),
-			builder.And(
-				builder.Eq{"entity_id": builder.
-					Select("project_id").
-					From("tasks").
-					Where(builder.In("id", entityIDs)),
-				// TODO parent project
-				},
-				builder.Eq{"entity_type": SubscriptionEntityProject},
-			),
-		)
-	}
-
-	return
-}
-
-// GetSubscription returns a matching subscription for an entity and user.
-// It will return the next parent of a subscription. That means for tasks, it will first look for a subscription for
-// that task, if there is none it will look for a subscription on the project the task belongs to.
-func GetSubscription(s *xorm.Session, entityType SubscriptionEntityType, entityID int64, a web.Auth) (subscription *Subscription, err error) {
-	subs, err := GetSubscriptions(s, entityType, entityID, a)
-	if err != nil || len(subs) == 0 {
-		return nil, err
-	}
-
-	return subs[0], nil
-}
-
-// GetSubscriptions returns a list of subscriptions to for an entity ID
-func GetSubscriptions(s *xorm.Session, entityType SubscriptionEntityType, entityID int64, a web.Auth) (subscriptions []*Subscription, err error) {
 	u, is := a.(*user.User)
 	if u != nil && !is {
 		return
 	}
+
+	subs, err := GetSubscriptionsForEntitiesAndUser(s, entityType, []int64{entityID}, u)
+	if err != nil || len(subs) == 0 || len(subs[entityID]) == 0 {
+		return nil, err
+	}
+
+	return subs[entityID][0], nil
+}
+
+// GetSubscriptionsForEntities returns a list of subscriptions to for an entity ID
+func GetSubscriptionsForEntities(s *xorm.Session, entityType SubscriptionEntityType, entityIDs []int64) (subscriptions map[int64][]*SubscriptionWithUser, err error) {
+	return getSubscriptionsForEntitiesAndUser(s, entityType, entityIDs, nil, false)
+}
+
+func GetSubscriptionsForEntitiesAndUser(s *xorm.Session, entityType SubscriptionEntityType, entityIDs []int64, u *user.User) (subscriptions map[int64][]*SubscriptionWithUser, err error) {
+	return getSubscriptionsForEntitiesAndUser(s, entityType, entityIDs, u, true)
+}
+
+func GetSubscriptionsForEntity(s *xorm.Session, entityType SubscriptionEntityType, entityID int64) (subscriptions []*SubscriptionWithUser, err error) {
+	subs, err := GetSubscriptionsForEntities(s, entityType, []int64{entityID})
+	if err != nil || len(subs[entityID]) == 0 {
+		return
+	}
+
+	return subs[entityID], nil
+}
+
+// This function returns a matching subscription for an entity and user.
+// It will return the next parent of a subscription. That means for tasks, it will first look for a subscription for
+// that task, if there is none it will look for a subscription on the project the task belongs to.
+// It will return a map where the key is the entity id and the value is a slice with all subscriptions for that entity.
+func getSubscriptionsForEntitiesAndUser(s *xorm.Session, entityType SubscriptionEntityType, entityIDs []int64, u *user.User, userOnly bool) (subscriptions map[int64][]*SubscriptionWithUser, err error) {
 	if err := entityType.validate(); err != nil {
 		return nil, err
 	}
 
+	rawSubscriptions := []*subscriptionResolved{}
+	entityIDString := utils.JoinInt64Slice(entityIDs, ", ")
+
+	var sUserCond string
+	if userOnly {
+		if u == nil {
+			return nil, &ErrMustProvideUser{}
+		}
+		sUserCond = " AND s.user_id = " + strconv.FormatInt(u.ID, 10)
+	}
+
 	switch entityType {
 	case SubscriptionEntityProject:
-		project, err := GetProjectSimpleByID(s, entityID)
+		err = s.SQL(`
-		if err != nil {
+WITH RECURSIVE project_hierarchy AS (
-			return nil, err
+    -- Base case: Start with the specified projects
-		}
+    SELECT
-		subs, err := GetSubscriptionsForProjects(s, []*Project{project}, u)
+        id,
-		if err != nil {
+        parent_project_id,
-			return nil, err
+        0 AS level,
-		}
+        id AS original_project_id
-		if _, has := subs[entityID]; has && subs[entityID] != nil {
+    FROM projects
-			return subs[entityID], nil
+    WHERE id IN (`+entityIDString+`)
-		}
 
-		for _, sub := range subs {
+    UNION ALL
-			// Fallback to the first non-nil subscription
-			if len(sub) > 0 {
-				return sub, nil
-			}
-		}
 
-		return nil, nil
+    -- Recursive case: Get parent projects
+    SELECT
+        p.id,
+        p.parent_project_id,
+        ph.level + 1,
+        ph.original_project_id
+    FROM projects p
+             INNER JOIN project_hierarchy ph ON p.id = ph.parent_project_id
+),
+
+subscription_hierarchy AS (
+    -- Check for project subscriptions (including parent projects)
+    SELECT
+        s.id,
+        s.entity_type,
+        s.entity_id,
+        s.created,
+        s.user_id,
+        CASE
+            WHEN s.entity_id = ph.original_project_id THEN 1  -- Direct project match
+            ELSE ph.level + 1  -- Parent projects
+            END AS priority,
+        ph.original_project_id
+    FROM subscriptions s
+             INNER JOIN project_hierarchy ph ON s.entity_id = ph.id
+    WHERE s.entity_type = ?`+sUserCond+`
+)
+
+SELECT
+    p.id AS original_entity_id,
+    sh.id AS subscription_id,
+    sh.entity_type,
+    sh.entity_id,
+    sh.created,
+    sh.user_id,
+    CASE
+        WHEN sh.priority = 1 THEN 'Direct Project'
+        ELSE 'Parent Project'
+        END 
+	AS subscription_level,
+    users.*
+FROM projects p
+         LEFT JOIN (
+    SELECT *,
+           ROW_NUMBER() OVER (PARTITION BY original_project_id, user_id ORDER BY priority) AS rn
+    FROM subscription_hierarchy
+) sh ON p.id = sh.original_project_id AND sh.rn = 1
+    LEFT JOIN users ON sh.user_id = users.id
+WHERE p.id IN (`+entityIDString+`)
+ORDER BY p.id, sh.user_id`, SubscriptionEntityProject).
+			Find(&rawSubscriptions)
 	case SubscriptionEntityTask:
-		subs, err := getSubscriptionsForTask(s, entityID, u)
+		err = s.SQL(`
+WITH RECURSIVE project_hierarchy AS (
+    -- Base case: Start with the projects associated with the tasks
+    SELECT
+        p.id,
+        p.parent_project_id,
+        0 AS level,
+        t.id AS task_id
+    FROM tasks t
+             JOIN projects p ON t.project_id = p.id
+    WHERE t.id IN (`+entityIDString+`)
+
+    UNION ALL
+
+    -- Recursive case: Get parent projects
+    SELECT
+        p.id,
+        p.parent_project_id,
+        ph.level + 1,
+        ph.task_id
+    FROM projects p
+             INNER JOIN project_hierarchy ph ON p.id = ph.parent_project_id
+),
+
+subscription_hierarchy AS (
+    -- Check for task subscriptions
+    SELECT
+        s.id,
+        s.entity_type,
+        s.entity_id,
+        s.created,
+        s.user_id,
+        1 AS priority,
+        t.id AS task_id
+    FROM subscriptions s
+             JOIN tasks t ON s.entity_id = t.id
+    WHERE s.entity_type = ? AND t.id IN (`+entityIDString+`)`+sUserCond+`
+
+    UNION ALL
+
+    -- Check for project subscriptions (including parent projects)
+    SELECT
+        s.id,
+        s.entity_type,
+        s.entity_id,
+        s.created,
+        s.user_id,
+        ph.level + 2 AS priority,
+        ph.task_id
+    FROM subscriptions s
+             INNER JOIN project_hierarchy ph ON s.entity_id = ph.id
+    WHERE s.entity_type = ?
+)
+
+SELECT
+    t.id AS original_entity_id,
+    sh.id AS subscription_id,
+    sh.entity_type,
+    sh.entity_id,
+    sh.created,
+    sh.user_id,
+    CASE
+        WHEN sh.entity_type = ? THEN 'Task'
+        WHEN sh.priority = ? THEN 'Direct Project'
+        ELSE 'Parent Project'
+    END
+    AS subscription_level,
+	users.*
+FROM tasks t
+    LEFT JOIN (
+    SELECT *,
+           ROW_NUMBER() OVER (PARTITION BY task_id, user_id ORDER BY priority) AS rn
+    FROM subscription_hierarchy
+) sh ON t.id = sh.task_id AND sh.rn = 1
+    LEFT JOIN users ON sh.user_id = users.id
+WHERE t.id IN (`+entityIDString+`)
+ORDER BY t.id, sh.user_id`,
+			SubscriptionEntityTask, SubscriptionEntityProject, SubscriptionEntityTask, SubscriptionEntityProject).
+			Find(&rawSubscriptions)
+	}
 	if err != nil {
 		return nil, err
 	}
 
-		for _, sub := range subs {
+	subscriptions = make(map[int64][]*SubscriptionWithUser)
-			// The subscriptions might also contain the immediate parent subscription, if that exists.
+	for _, sub := range rawSubscriptions {
-			// This loop makes sure to only return the task subscription if it exists. The fallback
-			// happens in the next if after the loop.
-			if sub.EntityID == entityID && sub.EntityType == SubscriptionEntityTask {
-				return []*Subscription{sub}, nil
-			}
-		}
 
-		if len(subs) > 0 {
+		if sub.Subscription.EntityID == 0 {
-			return subs, nil
-		}
-
-		projects, err := GetProjectsSimplByTaskIDs(s, []int64{entityID})
-		if err != nil {
-			return nil, err
-		}
-
-		projectSubscriptions, err := GetSubscriptionsForProjects(s, projects, u)
-		if err != nil {
-			return nil, err
-		}
-
-		if _, has := projectSubscriptions[projects[0].ID]; has {
-			return projectSubscriptions[projects[0].ID], nil
-		}
-
-		for _, psub := range projectSubscriptions {
-			// Fallback to the first non-nil subscription
-			if len(psub) > 0 {
-				return psub, nil
-			}
-		}
-
-		return subs, nil
-	}
-
-	return
-}
-
-func GetSubscriptionsForProjects(s *xorm.Session, projects []*Project, a web.Auth) (projectsToSubscriptions map[int64][]*Subscription, err error) {
-	u, is := a.(*user.User)
-	if u != nil && !is {
-		return
-	}
-
-	var ps = make(map[int64]*Project)
-	origProjectIDs := make([]int64, 0, len(projects))
-	allProjectIDs := make([]int64, 0, len(projects))
-
-	for _, p := range projects {
-		ps[p.ID] = p
-		origProjectIDs = append(origProjectIDs, p.ID)
-		allProjectIDs = append(allProjectIDs, p.ID)
-	}
-
-	// We can't just use the projects we have, we need to fetch the parents
-	// because they may not be loaded in the same object
-
-	for _, p := range projects {
-		if p.ParentProjectID == 0 {
 			continue
 		}
 
-		if _, has := ps[p.ParentProjectID]; has {
+		_, has := subscriptions[sub.OriginalEntityID]
-			continue
+		if !has {
+			subscriptions[sub.OriginalEntityID] = []*SubscriptionWithUser{}
 		}
 
-		parents, err := GetAllParentProjects(s, p.ID)
+		sub.Subscription.ID = sub.SubscriptionID
-		if err != nil {
+		if sub.User != nil {
-			return nil, err
+			sub.User.ID = sub.UserID
 		}
 
-		// Walk the tree up until we reach the top
+		subscriptions[sub.OriginalEntityID] = append(subscriptions[sub.OriginalEntityID], &sub.SubscriptionWithUser)
-		var parent = parents[p.ParentProjectID] // parent now has a pointer…
-		ps[p.ID].ParentProject = parents[p.ParentProjectID]
-		for parent != nil {
-			allProjectIDs = append(allProjectIDs, parent.ID)
-			parent = parents[parent.ParentProjectID] // … which means we can update it here and then update the pointer in the map
-		}
 	}
 
-	var subscriptions []*Subscription
+	return subscriptions, nil
-	if u != nil {
-		err = s.
-			Where("user_id = ?", u.ID).
-			And(getSubscriberCondForEntities(SubscriptionEntityProject, allProjectIDs)).
-			Find(&subscriptions)
-	} else {
-		err = s.
-			And(getSubscriberCondForEntities(SubscriptionEntityProject, allProjectIDs)).
-			Find(&subscriptions)
-	}
-	if err != nil {
-		return nil, err
-	}
-
-	projectsToSubscriptions = make(map[int64][]*Subscription)
-	for _, sub := range subscriptions {
-		sub.Entity = sub.EntityType.String()
-		projectsToSubscriptions[sub.EntityID] = append(projectsToSubscriptions[sub.EntityID], sub)
-	}
-
-	// Rearrange so that subscriptions trickle down
-
-	for _, eID := range origProjectIDs {
-		// If the current project does not have a subscription, climb up the tree until a project has one,
-		// then use that subscription for all child projects
-		_, has := projectsToSubscriptions[eID]
-		_, hasProject := ps[eID]
-		if !has && hasProject {
-			_, exists := ps[eID]
-			if !exists {
-				continue
-			}
-			var parent = ps[eID].ParentProject
-			for parent != nil {
-				sub, has := projectsToSubscriptions[parent.ID]
-				projectsToSubscriptions[eID] = sub
-				parent = parent.ParentProject
-				if has { // reached the top of the tree
-					break
-				}
-			}
-		}
-	}
-
-	return projectsToSubscriptions, nil
-}
-
-func getSubscriptionsForTask(s *xorm.Session, taskID int64, u *user.User) (subscriptions []*Subscription, err error) {
-	if u != nil {
-		err = s.
-			Where("user_id = ?", u.ID).
-			And(getSubscriberCondForEntities(SubscriptionEntityTask, []int64{taskID})).
-			Find(&subscriptions)
-	} else {
-		err = s.
-			And(getSubscriberCondForEntities(SubscriptionEntityTask, []int64{taskID})).
-			Find(&subscriptions)
-	}
-	if err != nil {
-		return nil, err
-	}
-
-	for _, sub := range subscriptions {
-		sub.Entity = sub.EntityType.String()
-	}
-
-	return
-}
-
-func getSubscribersForEntity(s *xorm.Session, entityType SubscriptionEntityType, entityID int64) (subscriptions []*Subscription, err error) {
-	if err := entityType.validate(); err != nil {
-		return nil, err
-	}
-
-	subs, err := GetSubscriptions(s, entityType, entityID, nil)
-	if err != nil {
-		return
-	}
-
-	userIDs := []int64{}
-	subscriptions = make([]*Subscription, 0, len(subs))
-	for _, subscription := range subs {
-		userIDs = append(userIDs, subscription.UserID)
-		subscriptions = append(subscriptions, subscription)
-	}
-
-	users, err := user.GetUsersByIDs(s, userIDs)
-	if err != nil {
-		return
-	}
-
-	for _, subscription := range subscriptions {
-		subscription.User = users[subscription.UserID]
-	}
-	return
 }

pkg/models/subscription_test.go

@@ -52,7 +52,6 @@ func TestSubscription_Create(t *testing.T) {
 		sb := &Subscription{
 			Entity:   "task",
 			EntityID: 1,
-			UserID:   u.ID,
 		}
 
 		can, err := sb.CanCreate(s, u)
@@ -61,7 +60,6 @@ func TestSubscription_Create(t *testing.T) {
 
 		err = sb.Create(s, u)
 		require.NoError(t, err)
-		assert.NotNil(t, sb.User)
 
 		db.AssertExists(t, "subscriptions", map[string]interface{}{
 			"entity_type": 3,
@@ -69,6 +67,26 @@ func TestSubscription_Create(t *testing.T) {
 			"user_id":     u.ID,
 		}, false)
 	})
+	t.Run("already exists", func(t *testing.T) {
+		db.LoadAndAssertFixtures(t)
+		s := db.NewSession()
+		defer s.Close()
+
+		sb := &Subscription{
+			Entity:   "task",
+			EntityID: 2,
+			UserID:   u.ID,
+		}
+
+		can, err := sb.CanCreate(s, u)
+		require.NoError(t, err)
+		assert.True(t, can)
+
+		err = sb.Create(s, u)
+		require.Error(t, err)
+		terr := &ErrSubscriptionAlreadyExists{}
+		assert.ErrorAs(t, err, &terr)
+	})
 	t.Run("forbidden for link shares", func(t *testing.T) {
 		db.LoadAndAssertFixtures(t)
 		s := db.NewSession()
@@ -86,7 +104,7 @@ func TestSubscription_Create(t *testing.T) {
 		require.Error(t, err)
 		assert.False(t, can)
 	})
-	t.Run("noneixsting project", func(t *testing.T) {
+	t.Run("nonexisting project", func(t *testing.T) {
 		db.LoadAndAssertFixtures(t)
 		s := db.NewSession()
 		defer s.Close()
@@ -240,7 +258,7 @@ func TestSubscriptionGet(t *testing.T) {
 			s := db.NewSession()
 			defer s.Close()
 
-			sub, err := GetSubscription(s, SubscriptionEntityProject, 12, u)
+			sub, err := GetSubscriptionForUser(s, SubscriptionEntityProject, 12, u)
 			require.NoError(t, err)
 			assert.NotNil(t, sub)
 			assert.Equal(t, int64(3), sub.ID)
@@ -250,7 +268,7 @@ func TestSubscriptionGet(t *testing.T) {
 			s := db.NewSession()
 			defer s.Close()
 
-			sub, err := GetSubscription(s, SubscriptionEntityTask, 22, u)
+			sub, err := GetSubscriptionForUser(s, SubscriptionEntityTask, 22, u)
 			require.NoError(t, err)
 			assert.NotNil(t, sub)
 			assert.Equal(t, int64(4), sub.ID)
@@ -263,7 +281,7 @@ func TestSubscriptionGet(t *testing.T) {
 			defer s.Close()
 
 			// Project 25 belongs to project 12 where user 6 has subscribed to
-			sub, err := GetSubscription(s, SubscriptionEntityProject, 25, u)
+			sub, err := GetSubscriptionForUser(s, SubscriptionEntityProject, 25, u)
 			require.NoError(t, err)
 			assert.NotNil(t, sub)
 			assert.Equal(t, int64(12), sub.EntityID)
@@ -275,7 +293,7 @@ func TestSubscriptionGet(t *testing.T) {
 			defer s.Close()
 
 			// Project 26 belongs to project 25 which belongs to project 12 where user 6 has subscribed to
-			sub, err := GetSubscription(s, SubscriptionEntityProject, 26, u)
+			sub, err := GetSubscriptionForUser(s, SubscriptionEntityProject, 26, u)
 			require.NoError(t, err)
 			assert.NotNil(t, sub)
 			assert.Equal(t, int64(12), sub.EntityID)
@@ -287,7 +305,7 @@ func TestSubscriptionGet(t *testing.T) {
 			defer s.Close()
 
 			// Task 39 belongs to project 25 which belongs to project 12 where the user has subscribed
-			sub, err := GetSubscription(s, SubscriptionEntityTask, 39, u)
+			sub, err := GetSubscriptionForUser(s, SubscriptionEntityTask, 39, u)
 			require.NoError(t, err)
 			assert.NotNil(t, sub)
 			// assert.Equal(t, int64(2), sub.ID) TODO
@@ -298,7 +316,7 @@ func TestSubscriptionGet(t *testing.T) {
 			defer s.Close()
 
 			// Task 21 belongs to project 32 which the user has subscribed to
-			sub, err := GetSubscription(s, SubscriptionEntityTask, 21, u)
+			sub, err := GetSubscriptionForUser(s, SubscriptionEntityTask, 21, u)
 			require.NoError(t, err)
 			assert.NotNil(t, sub)
 			assert.Equal(t, int64(8), sub.ID)
@@ -309,7 +327,7 @@ func TestSubscriptionGet(t *testing.T) {
 		s := db.NewSession()
 		defer s.Close()
 
-		_, err := GetSubscription(s, 2342, 21, u)
+		_, err := GetSubscriptionForUser(s, 2342, 21, u)
 		require.Error(t, err)
 		assert.True(t, IsErrUnknownSubscriptionEntityType(err))
 	})
@@ -318,7 +336,7 @@ func TestSubscriptionGet(t *testing.T) {
 		s := db.NewSession()
 		defer s.Close()
 
-		sub, err := GetSubscription(s, SubscriptionEntityTask, 18, u)
+		sub, err := GetSubscriptionForUser(s, SubscriptionEntityTask, 18, u)
 		require.NoError(t, err)
 		assert.Equal(t, int64(9), sub.ID)
 	})

pkg/models/tasks.go

@@ -1573,10 +1573,11 @@ func (t *Task) ReadOne(s *xorm.Session, a web.Auth) (err error) {
 
 	*t = *taskMap[t.ID]
 
-	t.Subscription, err = GetSubscription(s, SubscriptionEntityTask, t.ID, a)
+	subs, err := GetSubscriptionForUser(s, SubscriptionEntityTask, t.ID, a)
 	if err != nil && IsErrProjectDoesNotExist(err) {
 		return nil
 	}
+	t.Subscription = &subs.Subscription
 
 	return
 }

pkg/utils/strings.go

@@ -0,0 +1,31 @@
+// Vikunja is a to-do list application to facilitate your life.
+// Copyright 2018-present Vikunja and contributors. All rights reserved.
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public Licensee as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public Licensee for more details.
+//
+// You should have received a copy of the GNU Affero General Public Licensee
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+package utils
+
+import "strconv"
+
+func JoinInt64Slice(ints []int64, delim string) string {
+	b := ""
+	for _, v := range ints {
+		if len(b) > 0 {
+			b += delim
+		}
+		b += strconv.FormatInt(v, 10)
+	}
+
+	return b
+}