diff --git a/.editorconfig b/.editorconfig
new file mode 100644
index 0000000..3d25c9a
--- /dev/null
+++ b/.editorconfig
@@ -0,0 +1,4 @@
+[*.cs]
+
+# CA1822: Member als statisch markieren
+dotnet_diagnostic.CA1822.severity = suggestion
diff --git a/UserService.DatabaseLayer/DataModels/ModelBuilderExtensions.cs b/UserService.DatabaseLayer/DataModels/ModelBuilderExtensions.cs
index d06cd66..68710ae 100644
--- a/UserService.DatabaseLayer/DataModels/ModelBuilderExtensions.cs
+++ b/UserService.DatabaseLayer/DataModels/ModelBuilderExtensions.cs
@@ -1,4 +1,5 @@
-using Microsoft.EntityFrameworkCore;
+using System;
+using Microsoft.EntityFrameworkCore;
 using System.Collections.Generic;
 
 namespace UserService.DatabaseLayer.DataModels
@@ -7,6 +8,7 @@ namespace UserService.DatabaseLayer.DataModels
     {
         public static void Seed(this ModelBuilder modelBuilder)
         {
+            if (modelBuilder == null) throw new ArgumentNullException(nameof(modelBuilder));
             var groups = new OrganizationUnit { CommonName = "Groups", Id = -1 };
             var users = new OrganizationUnit { CommonName = "Users", Id = -2 };
             var germany = new OrganizationUnit{CommonName = "Germany", Id = -6, ParentId = -2};
@@ -25,6 +27,7 @@ namespace UserService.DatabaseLayer.DataModels
 
         public static void CreateRelations(this ModelBuilder modelBuilder)
         {
+            if (modelBuilder == null) throw new ArgumentNullException(nameof(modelBuilder));
             modelBuilder.Entity<UserMember>()
                 .HasKey(bc => new { bc.MemberId, bc.UserId });
             modelBuilder.Entity<UserMember>()
@@ -47,6 +50,7 @@ namespace UserService.DatabaseLayer.DataModels
     {
         public static IEnumerable<SecurityGroup> GetSecurityGroups(this User user)
         {
+            if (user == null) throw new ArgumentNullException(nameof(user));
             foreach (var userMember in user.MemberOf)
             {
                 if (userMember.Member is SecurityGroup securityGroup)
@@ -62,6 +66,7 @@ namespace UserService.DatabaseLayer.DataModels
     {
         public static IEnumerable<User> GetUsers(this SecurityGroup securityGroup)
         {
+            if (securityGroup == null) throw new ArgumentNullException(nameof(securityGroup));
             foreach (var userMember in securityGroup.Members)
             {
                 if (userMember.User is null) continue;
diff --git a/UserService.DatabaseLayer/DataModels/Node.cs b/UserService.DatabaseLayer/DataModels/Node.cs
index c5b63f1..ed5c873 100644
--- a/UserService.DatabaseLayer/DataModels/Node.cs
+++ b/UserService.DatabaseLayer/DataModels/Node.cs
@@ -1,7 +1,7 @@
-using System;
+#nullable enable
+using System;
 using System.Collections.Generic;
 using System.ComponentModel.DataAnnotations;
-using System.Text;
 
 namespace UserService.DatabaseLayer.DataModels
 {
diff --git a/UserService.DatabaseLayer/Repository/BaseRepository.cs b/UserService.DatabaseLayer/Repository/BaseRepository.cs
index 2df2c97..b50f2ee 100644
--- a/UserService.DatabaseLayer/Repository/BaseRepository.cs
+++ b/UserService.DatabaseLayer/Repository/BaseRepository.cs
@@ -12,7 +12,7 @@ namespace UserService.DatabaseLayer.Repository
 {
     public class BaseRepository<T> where T : Node
     {
-        protected readonly Func<UserServiceDbContext, DbSet<T>> Context;
+        protected Func<UserServiceDbContext, DbSet<T>> Context { get; }
 
         protected BaseRepository(Func<UserServiceDbContext, DbSet<T>> context)
         {
@@ -22,27 +22,27 @@ namespace UserService.DatabaseLayer.Repository
         public virtual async Task<IReadOnlyList<T>> GetAllAsync(Expression<Func<T, bool>>? predicate = null, CancellationToken token = default)
         {
             await using var db = new UserServiceDbContext();
-            return await Context(db).Include(x => x.Parent).WhereOrDefault(predicate).ToListAsync(token);
+            return await Context(db).Include(x => x.Parent).WhereOrDefault(predicate).ToListAsync(token).ConfigureAwait(false);
         }
 
         public async Task<T?> GetAsync(Expression<Func<T, bool>> predicate, CancellationToken token = default)
         {
             await using var db = new UserServiceDbContext();
-            return await Context(db).FirstOrDefaultAsync(predicate, token);
+            return await Context(db).FirstOrDefaultAsync(predicate, token).ConfigureAwait(false);
         }
 
         public async Task AddAsync(T entity, CancellationToken token = default)
         {
             await using var db = new UserServiceDbContext();
-            await Context(db).AddAsync(@entity, token);
-            await db.SaveChangesAsync(token);
+            await Context(db).AddAsync(@entity, token).ConfigureAwait(false);
+            await db.SaveChangesAsync(token).ConfigureAwait(false);
         }
 
         public async Task<bool> UpdateAsync(T entity, CancellationToken token = default)
         {
             await using var db = new UserServiceDbContext();
             Context(db).Update(entity);
-            var items= await db.SaveChangesAsync(token);
+            var items= await db.SaveChangesAsync(token).ConfigureAwait(false);
             return items > 0;
         }
 
@@ -50,7 +50,7 @@ namespace UserService.DatabaseLayer.Repository
         {
             await using var db = new UserServiceDbContext();
             Context(db).Remove(entity);
-            await db.SaveChangesAsync(token);
+            await db.SaveChangesAsync(token).ConfigureAwait(false);
         }
     }
 }
\ No newline at end of file
diff --git a/UserService.DatabaseLayer/Repository/OrganizationUnitsRepository.cs b/UserService.DatabaseLayer/Repository/OrganizationUnitsRepository.cs
index 08e5222..7a1fa41 100644
--- a/UserService.DatabaseLayer/Repository/OrganizationUnitsRepository.cs
+++ b/UserService.DatabaseLayer/Repository/OrganizationUnitsRepository.cs
@@ -24,7 +24,7 @@ namespace UserService.DatabaseLayer.Repository
             var rootOus = await Context(db)
                 .Include(x => x.Parent)
                 .WhereOrDefault(predicate)
-                .ToListAsync(cancellationToken: token);
+                .ToListAsync(cancellationToken: token).ConfigureAwait(false);
 
             IEnumerable<OrganizationUnit> Rec(Node node)
             {
diff --git a/UserService.DatabaseLayer/UserService.DatabaseLayer.csproj b/UserService.DatabaseLayer/UserService.DatabaseLayer.csproj
index c6062ce..fc60665 100644
--- a/UserService.DatabaseLayer/UserService.DatabaseLayer.csproj
+++ b/UserService.DatabaseLayer/UserService.DatabaseLayer.csproj
@@ -7,11 +7,15 @@
     </PropertyGroup>
 
     <ItemGroup>
-      <PackageReference Include="Microsoft.EntityFrameworkCore.Design" Version="3.1.6">
+      <PackageReference Include="Microsoft.CodeAnalysis.FxCopAnalyzers" Version="3.3.0">
         <PrivateAssets>all</PrivateAssets>
         <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
       </PackageReference>
-      <PackageReference Include="Microsoft.EntityFrameworkCore.Sqlite" Version="3.1.6" />
+      <PackageReference Include="Microsoft.EntityFrameworkCore.Design" Version="3.1.7">
+        <PrivateAssets>all</PrivateAssets>
+        <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+      </PackageReference>
+      <PackageReference Include="Microsoft.EntityFrameworkCore.Sqlite" Version="3.1.7" />
     </ItemGroup>
 
 </Project>
diff --git a/UserService.Test/UnitTest1.cs b/UserService.Test/UnitTest1.cs
index 4fd7428..0b70fc3 100644
--- a/UserService.Test/UnitTest1.cs
+++ b/UserService.Test/UnitTest1.cs
@@ -19,10 +19,10 @@ namespace UserService.Test
         public async Task Test1()
         {
             await using var db = new UserServiceDbContext();
-            var user = await db.Users.FirstOrDefaultAsync();
-            var secGroup = await db.SecurityGroups.FirstOrDefaultAsync();
-            var ous = await db.OrganizationUnits.ToListAsync();
-            var mo = await db.UserMembers.ToListAsync();
+            var user = await db.Users.FirstOrDefaultAsync().ConfigureAwait(false);
+            var secGroup = await db.SecurityGroups.FirstOrDefaultAsync().ConfigureAwait(false);
+            var ous = await db.OrganizationUnits.ToListAsync().ConfigureAwait(false);
+            var mo = await db.UserMembers.ToListAsync().ConfigureAwait(false);
 
             var securityGroupsOfUser = user.GetSecurityGroups();
             var usersOfSecurityGroup = secGroup.GetUsers();
@@ -38,7 +38,7 @@ namespace UserService.Test
         public async Task Test2()
         {
             await using var db = new UserServiceDbContext();
-            var ous = await db.OrganizationUnits.ToListAsync();
+            var ous = await db.OrganizationUnits.ToListAsync().ConfigureAwait(false);
             var sb = new StringBuilder();
             NewMethod(ous, null, 0, ref sb);
             var result = sb.ToString();
diff --git a/UserService.Test/UserService.Test.csproj b/UserService.Test/UserService.Test.csproj
index 022e46a..48b2f52 100644
--- a/UserService.Test/UserService.Test.csproj
+++ b/UserService.Test/UserService.Test.csproj
@@ -1,4 +1,4 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
     <TargetFramework>netcoreapp3.1</TargetFramework>
@@ -7,9 +7,13 @@
   </PropertyGroup>
 
   <ItemGroup>
+    <PackageReference Include="Microsoft.CodeAnalysis.FxCopAnalyzers" Version="3.3.0">
+      <PrivateAssets>all</PrivateAssets>
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+    </PackageReference>
     <PackageReference Include="nunit" Version="3.12.0" />
     <PackageReference Include="NUnit3TestAdapter" Version="3.17.0" />
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.6.1" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.7.0" />
   </ItemGroup>
 
   <ItemGroup>
diff --git a/UserService.db b/UserService.db
index dd1435b..e800eca 100644
Binary files a/UserService.db and b/UserService.db differ
diff --git a/UserService.sln b/UserService.sln
index f9488a0..3136372 100644
--- a/UserService.sln
+++ b/UserService.sln
@@ -9,6 +9,11 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "UserService.Test", "UserSer
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "UserService.DatabaseLayer", "UserService.DatabaseLayer\UserService.DatabaseLayer.csproj", "{4505C991-7E39-416F-94E5-D906DD0D90F9}"
 EndProject
+Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Solution Items", "Solution Items", "{A8D411B0-CD71-4448-9D4F-12898D0CCDD6}"
+	ProjectSection(SolutionItems) = preProject
+		.editorconfig = .editorconfig
+	EndProjectSection
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
diff --git a/UserService/Pages/Directory.razor.cs b/UserService/Pages/Directory.razor.cs
index 31b6510..2e238b7 100644
--- a/UserService/Pages/Directory.razor.cs
+++ b/UserService/Pages/Directory.razor.cs
@@ -1,5 +1,4 @@
-using System;
-using System.Collections.Generic;
+using System.Collections.Generic;
 using System.Linq;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Components;
@@ -27,14 +26,14 @@ namespace UserService.Pages
         private async void OnSelectedNodeChanged(Node? value)
         {
             if (value == null) return;
-            Members = await UsersRepository.GetAllAsync(x => x.ParentId == value.Id);
+            Members = await UsersRepository.GetAllAsync(x => x.ParentId == value.Id).ConfigureAwait(false);
         }
 
-        public IReadOnlyList<Member> Members { get; set; }
+        public IReadOnlyList<Member>? Members { get; set; }
 
-        [Inject] public IOrganizationUnitsRepository OuRepository { get; set; }
+        [Inject] public IOrganizationUnitsRepository OuRepository { get; set; } = null!;
 
-        [Inject] public IUsersRepository UsersRepository { get; set; }
+        [Inject] public IUsersRepository UsersRepository { get; set; } = null!;
 
 
         protected override async Task OnInitializedAsync()
diff --git a/UserService/Pages/SecurityGroups.razor b/UserService/Pages/SecurityGroups.razor
index e21b1e7..21b50da 100644
--- a/UserService/Pages/SecurityGroups.razor
+++ b/UserService/Pages/SecurityGroups.razor
@@ -4,7 +4,7 @@
 
 <h1>Table of all security groups</h1>
 
-@if (SecurityGroups is null)
+@if (Groups is null)
 {
 <p>
     <em>Loading...</em>
@@ -12,7 +12,7 @@
 }
 else
 {
-<DataGrid TItem="SecurityGroup" Data="@SecurityGroups">
+<DataGrid TItem="SecurityGroup" Data="@Groups">
     <DataGridCommandColumn TItem="User" />
     <DataGridColumn TItem="SecurityGroup" Field="@nameof(SecurityGroup.Id)" Caption="#" Sortable="false" />
     <DataGridColumn TItem="SecurityGroup" Field="@nameof(SecurityGroup.CommonName)" Caption="CN" Editable="true" />
diff --git a/UserService/Pages/SecurityGroups.razor.cs b/UserService/Pages/SecurityGroups.razor.cs
index b1269ba..1c65bfd 100644
--- a/UserService/Pages/SecurityGroups.razor.cs
+++ b/UserService/Pages/SecurityGroups.razor.cs
@@ -8,18 +8,18 @@ namespace UserService.Pages
 {
     public class SecurityGroupsBase : ComponentBase
     {
-        [Inject] private ISecurityGroupsRepository? SecurityGroupsRepository { get; set; }
-        [Inject] private IOrganizationUnitsRepository? OrganizationUnitsRepository { get; set; }
+        [Inject] private ISecurityGroupsRepository SecurityGroupsRepository { get; set; } = null!;
+        [Inject] private IOrganizationUnitsRepository OrganizationUnitsRepository { get; set; } = null!;
 
-        protected bool DialogIsOpen;
-        protected SecurityGroup? SecurityGroupToEdit;
+        protected bool DialogIsOpen { get; set; }
+        protected SecurityGroup? SecurityGroupToEdit { get; set; }
 
-        protected IReadOnlyList<SecurityGroup>? SecurityGroups;
-        protected IReadOnlyList<OrganizationUnit>? OrganizationUnits;
+        protected IReadOnlyList<SecurityGroup>? Groups { get; set; }
+        protected IReadOnlyList<OrganizationUnit>? OrganizationUnits { get; set; }
 
         protected override async Task OnInitializedAsync()
         {
-            SecurityGroups = await SecurityGroupsRepository.GetAllAsync().ConfigureAwait(false);
+            Groups = await SecurityGroupsRepository.GetAllAsync().ConfigureAwait(false);
             OrganizationUnits = await OrganizationUnitsRepository.GetAllAsync().ConfigureAwait(false);
         }
 
diff --git a/UserService/Pages/Users.razor b/UserService/Pages/Users.razor
index 344483d..16e99a6 100644
--- a/UserService/Pages/Users.razor
+++ b/UserService/Pages/Users.razor
@@ -29,24 +29,23 @@ else
         <DataGridColumn TItem="User" Field="@nameof(User.FirstName)" Caption="First Name" Editable="true"/>
         <DataGridColumn TItem="User" Field="@nameof(User.LastName)" Caption="Last Name" Editable="true"/>
         <DataGridColumn TItem="User" Field="@nameof(User.EMail)" Caption="EMail" Editable="true"/>
-        <DataGridSelectColumn TItem="User" Field="@nameof(User.Parent)" Caption="Parent" Editable="true">
+        <DataGridSelectColumn TItem="User" Field="@nameof(User.ParentId)" Caption="Parent" Editable="true">
             <DisplayTemplate>
                 @{
-                    var name = ((User) context).Parent?.CommonName ?? "-";
+                    var name = ((User) context ).Parent?.CommonName ?? "-";
                     @name
                 }
 
             </DisplayTemplate>
             <EditTemplate>
-                @{
-                    <Blazorise.SelectEdit TValue="User" SelectedValue="@((User)(context.CellValue))" SelectedValueChanged="@(v => context.CellValue = v)">
+               
+                    <Select TValue="int" SelectedValue="@((int)(context.CellValue))" SelectedValueChanged="@(v => context.CellValue = v)" >
                     @foreach (var item in OrganizationUnits)
                     {
-
-                        <SelectItem TValue="OrganizationUnit" Value="@(item)">@item.CommonName</SelectItem>
+                        <SelectItem TValue="int" Value="@(item.Id)">@item.CommonName</SelectItem>
                     }
-                    </Blazorise.SelectEdit>
-                }
+                    </Select>
+                
 
             </EditTemplate>
         </DataGridSelectColumn>
diff --git a/UserService/Pages/Users.razor.cs b/UserService/Pages/Users.razor.cs
index cc16240..a134c6f 100644
--- a/UserService/Pages/Users.razor.cs
+++ b/UserService/Pages/Users.razor.cs
@@ -1,5 +1,7 @@
-using Microsoft.AspNetCore.Components;
+using System;
+using Microsoft.AspNetCore.Components;
 using System.Collections.Generic;
+using System.Linq;
 using System.Threading.Tasks;
 using Blazorise.DataGrid;
 using Microsoft.JSInterop;
@@ -20,19 +22,21 @@ namespace UserService.Pages
 
         protected override async Task OnInitializedAsync()
         {
-            Users = await UsersRepository.GetAllAsync();
+            Users = await UsersRepository.GetAllAsync().ConfigureAwait(false);
             OrganizationUnits = await OrganizationUnitsRepository.GetAllAsync().ConfigureAwait(false);
         }
 
         protected async Task RowInsertedCallback(SavedRowItem<User, Dictionary<string, object>> arg)
         {
+            if (arg == null) throw new ArgumentNullException(nameof(arg));
             var user = arg.Item;
             user.ParentId = -2;
-            await UsersRepository.AddAsync(user);
+            await UsersRepository.AddAsync(user).ConfigureAwait(false);
         }
 
         protected async Task RowDeletingCallback(CancellableRowChange<User> arg)
         {
+            if (arg == null) throw new ArgumentNullException(nameof(arg));
             var confirmed = await JsRuntime.InvokeAsync<bool>("confirm",
                 $"You are about to delete the user {arg.Item.FullName}. Are you sure?").ConfigureAwait(false);
             if (confirmed)
@@ -46,7 +50,10 @@ namespace UserService.Pages
         
             protected async Task RowUpdatingCallback(CancellableRowChange<User, Dictionary<string, object>> arg)
             {
-                var result = await UsersRepository.UpdateAsync(arg.Item);
+                if (arg == null) throw new ArgumentNullException(nameof(arg));
+                var user = arg.Item;
+                user.Parent = OrganizationUnits.FirstOrDefault(x => x.Id == (int?)arg.Values[nameof(Node.ParentId)]);
+                var result = await UsersRepository.UpdateAsync(user).ConfigureAwait(false);
                 arg.Cancel = !result;
             }
 
diff --git a/UserService/Startup.cs b/UserService/Startup.cs
index dfd5430..8827107 100644
--- a/UserService/Startup.cs
+++ b/UserService/Startup.cs
@@ -1,3 +1,4 @@
+using System;
 using Blazorise;
 using Blazorise.Bootstrap;
 using Blazorise.Icons.FontAwesome;
@@ -40,6 +41,7 @@ namespace UserService
         // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
         public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
         {
+            if (app == null) throw new ArgumentNullException(nameof(app));
             if (env.IsDevelopment())
             {
                 app.UseDeveloperExceptionPage();
diff --git a/UserService/UserService.csproj b/UserService/UserService.csproj
index ebd1211..1bffdf8 100644
--- a/UserService/UserService.csproj
+++ b/UserService/UserService.csproj
@@ -5,6 +5,10 @@
     <Nullable>enable</Nullable>
   </PropertyGroup>
 
+  <ItemGroup>
+    <None Include="..\.editorconfig" Link=".editorconfig" />
+  </ItemGroup>
+
   <ItemGroup>
     <ProjectReference Include="..\UserService.DatabaseLayer\UserService.DatabaseLayer.csproj" />
   </ItemGroup>
@@ -15,6 +19,10 @@
     <PackageReference Include="Blazorise.Icons.FontAwesome" Version="0.9.1.2" />
     <PackageReference Include="Blazorise.Sidebar" Version="0.9.1.2" />
     <PackageReference Include="Blazorise.TreeView" Version="0.9.1.2" />
+    <PackageReference Include="Microsoft.CodeAnalysis.FxCopAnalyzers" Version="3.3.0">
+      <PrivateAssets>all</PrivateAssets>
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+    </PackageReference>
   </ItemGroup>
 
 </Project>