[init:] database service for a following implementation

DataStore/DatabaseService.cs

@@ -0,0 +1,166 @@
+using System;
+using System.Threading.Tasks;
+using Microsoft.EntityFrameworkCore;
+
+namespace Logof_Client;
+
+/// <summary>
+/// Zentrale Datenbankverwaltung für Logof Client.
+/// 
+/// Zuständig für:
+/// - PostgreSQL-Verbindung
+/// - EF Core DbContext
+/// - Datenbankmodelle
+/// - Migrationen
+/// - Verbindungstest
+/// </summary>
+public static class DatabseService
+{
+    private static DbContextOptions<LogofDbContext>? _options;
+
+    /// <summary>
+    /// Initialisiert die Datenbankverbindung.
+    /// Sollte einmal beim Programmstart aufgerufen werden.
+    /// </summary>
+    public static void Initialize(string connectionString)
+    {
+        if (string.IsNullOrWhiteSpace(connectionString))
+            throw new ArgumentException(
+                "Kein Datenbank-Connection-String angegeben.",
+                nameof(connectionString));
+
+        var builder = new DbContextOptionsBuilder<LogofDbContext>();
+
+        builder.UseNpgsql(connectionString);
+
+        _options = builder.Options;
+    }
+
+    /// <summary>
+    /// Erstellt einen neuen DbContext.
+    /// </summary>
+    public static LogofDbContext GetContext()
+    {
+        if (_options == null)
+            throw new InvalidOperationException(
+                "DB wurde noch nicht initialisiert. " +
+                "Rufen Sie DB.Initialize(...) auf.");
+
+        return new LogofDbContext(_options);
+    }
+
+    /// <summary>
+    /// Testet die Verbindung zum Datenbankserver.
+    /// </summary>
+    public static async Task<bool> TestConnectionAsync()
+    {
+        try
+        {
+            await using var db = GetContext();
+            return await db.Database.CanConnectAsync();
+        }
+        catch
+        {
+            return false;
+        }
+    }
+
+    /// <summary>
+    /// Erstellt bzw. aktualisiert das Datenbankschema
+    /// anhand der vorhandenen EF-Core-Migrationen.
+    /// </summary>
+    public static async Task MigrateAsync()
+    {
+        await using var db = GetContext();
+
+        await db.Database.MigrateAsync();
+    }
+}
+
+
+// ============================================================================
+// DATABASE CONTEXT
+// ============================================================================
+
+public class LogofDbContext : DbContext
+{
+    public DbSet<CustomerEx> Customers => Set<CustomerEx>();
+
+    public LogofDbContext(
+        DbContextOptions<LogofDbContext> options)
+        : base(options)
+    {
+    }
+
+    protected override void OnModelCreating(ModelBuilder modelBuilder)
+    {
+        base.OnModelCreating(modelBuilder);
+
+        // --------------------------------------------------------------------
+        // Customer
+        // --------------------------------------------------------------------
+
+        modelBuilder.Entity<CustomerEx>(entity =>
+        {
+            entity.ToTable("customers");
+
+            entity.HasKey(x => x.Id);
+
+            entity.Property(x => x.Id)
+                .ValueGeneratedOnAdd();
+
+            entity.Property(x => x.Name)
+                .HasMaxLength(255)
+                .IsRequired();
+
+            entity.Property(x => x.Description)
+                .HasMaxLength(4000);
+
+            entity.Property(x => x.SenderAddress)
+                .HasMaxLength(4000);
+
+            entity.Property(x => x.Separator)
+                .HasMaxLength(1)
+                .IsRequired();
+
+            // Optimistic Concurrency
+            entity.Property(x => x.Version)
+                .IsConcurrencyToken();
+
+            entity.Property(x => x.CreatedAt)
+                .IsRequired();
+
+            entity.Property(x => x.UpdatedAt)
+                .IsRequired();
+        });
+    }
+}
+
+
+// ============================================================================
+// DATABASE MODELS
+// ============================================================================
+
+public class CustomerEx
+{
+    public long Id { get; set; }
+
+    public string Name { get; set; } = "";
+
+    public string Description { get; set; } = "";
+
+    public string SenderAddress { get; set; } = "";
+
+    public char Separator { get; set; } = ',';
+
+    /// <summary>
+    /// Wird bei jeder Änderung erhöht.
+    /// Verhindert, dass zwei Benutzer sich gegenseitig
+    /// Änderungen überschreiben.
+    /// </summary>
+    public long Version { get; set; } = 1;
+
+    public DateTime CreatedAt { get; set; }
+
+    public DateTime UpdatedAt { get; set; }
+}

Logof Client.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
     <PropertyGroup>
         <OutputType>WinExe</OutputType>
-        <TargetFramework>net9.0</TargetFramework>
+        <TargetFramework>net10.0</TargetFramework>
         <Nullable>enable</Nullable>
         <BuiltInComInteropSupport>true</BuiltInComInteropSupport>
         <ApplicationManifest>app.manifest</ApplicationManifest>
@@ -24,6 +24,9 @@
         <PackageReference Include="Markdown.Avalonia" Version="11.0.3" />
         <PackageReference Include="Newtonsoft.Json" Version="13.0.4" />
         <PackageReference Include="PdfSharp" Version="6.1.1" />
+        <PackageReference Include="Microsoft.EntityFrameworkCore" Version="10.0.12" />
+        <PackageReference Include="Microsoft.EntityFrameworkCore.Design" Version="10.0.12" />
+        <PackageReference Include="Npgsql.EntityFrameworkCore.PostgreSQL" Version="10.0.3" />
     </ItemGroup>
 
     <ItemGroup>