Allow users to be uniquely identified by login

app/models/user.rb

@@ -481,6 +481,23 @@ class User < Principal
     end
   end
 
+  ##
+  # Returns the first user that matches (in this order), either:
+  # 1. The given ID
+  # 2. The given login
+  def self.find_by_unique(login_or_id)
+    matches = where(id: login_or_id).or(where(login: login_or_id)).to_a
+
+    case matches.length
+    when 0
+      raise ActiveRecord::RecordNotFound
+    when 1
+      return matches.first
+    else
+      return matches.find { |user| user.id.to_s == login_or_id.to_s }
+    end
+  end
+
   # Find a user account by matching the exact login and then a case-insensitive
   # version.  Exact matches will be given priority.
   def self.find_by_login(login)

lib/api/v3/users/users_api.rb

@@ -89,7 +89,7 @@ module API
             helpers ::API::V3::Users::UpdateUser
 
             before do
-              @user = User.find(params[:id])
+              @user = User.find_by_unique(params[:id])
             end
 
             get do

spec/models/user_spec.rb

@@ -46,21 +46,18 @@ describe User, type: :model do
   }
 
   describe 'a user with a long login (<= 256 chars)' do
+    let(:login) { 'a' * 256 }
     it 'is valid' do
-      user.login = 'a' * 256
+      user.login = login
       expect(user).to be_valid
     end
 
-    it 'may be stored in the database' do
-      user.login = 'a' * 256
-      expect(user.save).to be_truthy
-    end
-
     it 'may be loaded from the database' do
-      user.login = 'a' * 256
-      user.save
+      user.login = login
+      expect(user.save).to be_truthy
 
-      expect(User.find_by_login('a' * 256)).to eq(user)
+      expect(User.find_by_login(login)).to eq(user)
+      expect(User.find_by_unique(login)).to eq(user)
     end
   end
 

spec/requests/api/v3/user/user_resource_spec.rb

@@ -182,6 +182,22 @@ describe 'API v3 User resource', type: :request do
       end
     end
 
+    context 'get with login' do
+      let(:get_path) { api_v3_paths.user user.login }
+      before do
+        allow(User).to receive(:current).and_return current_user
+        get get_path
+      end
+
+      it 'should respond with 200' do
+        expect(subject.status).to eq(200)
+      end
+
+      it 'should respond with correct body' do
+        expect(subject.body).to be_json_eql(user.name.to_json).at_path('name')
+      end
+    end
+
     it_behaves_like 'handling anonymous user' do
       let(:path) { api_v3_paths.user user.id }
     end