Merge branch 'ab-use-exists' into 'master'

Change queries from using count to limit

See merge request gitlab-org/gitlab!27028

app/controllers/admin/serverless/domains_controller.rb

@@ -9,7 +9,7 @@ class Admin::Serverless::DomainsController < Admin::ApplicationController
   end
 
   def create
-    if PagesDomain.instance_serverless.count > 0
+    if PagesDomain.instance_serverless.exists?
       return redirect_to admin_serverless_domains_path, notice: _('An instance-level serverless domain already exists.')
     end
 
@@ -31,7 +31,7 @@ class Admin::Serverless::DomainsController < Admin::ApplicationController
   end
 
   def destroy
-    if domain.serverless_domain_clusters.count > 0
+    if domain.serverless_domain_clusters.exists?
       return redirect_to admin_serverless_domains_path,
                          status: :conflict,
                          notice: _('Domain cannot be deleted while associated to one or more clusters.')

lib/api/users.rb

@@ -206,11 +206,11 @@ module API
 
         conflict!('Email has already been taken') if params[:email] &&
             User.by_any_email(params[:email].downcase)
-                .where.not(id: user.id).count > 0
+                .where.not(id: user.id).exists?
 
         conflict!('Username has already been taken') if params[:username] &&
             User.by_username(params[:username])
-                .where.not(id: user.id).count > 0
+                .where.not(id: user.id).exists?
 
         user_params = declared_params(include_missing: false)