Optimize invoice performance with indexes and DTO

Added indexes for `ImportedAt` and a composite key on
`InvoiceNumber` and `SellerTaxId` to improve query performance.
Updated `AppDbContext` and EF Core migrations to reflect these
changes. Introduced `ZugferdInvoiceListDto` to optimize memory
usage by excluding large fields like `RawXml`. Updated the
frontend (`Index.cshtml`) and backend (`Index.cshtml.cs`) to use
the new DTO for better performance.

DXApp.TemplateKitProject/Data/AppDbContext.cs

@@ -6,4 +6,27 @@ namespace DXApp.TemplateKitProject.Data;
 public class AppDbContext(DbContextOptions<AppDbContext> options) : DbContext(options)
 {
     public DbSet<ZugferdInvoice> ZugferdInvoices { get; set; }
+
+    protected override void OnModelCreating(ModelBuilder modelBuilder)
+    {
+        base.OnModelCreating(modelBuilder);
+
+        modelBuilder.Entity<ZugferdInvoice>(entity =>
+        {
+            // Index für Performance-Optimierung der Rechnungsliste
+            entity.HasIndex(e => e.ImportedAt)
+                .HasDatabaseName("IX_ZugferdInvoices_ImportedAt");
+
+            // Index für Duplikatprüfung
+            entity.HasIndex(e => new { e.InvoiceNumber, e.SellerTaxId })
+                .HasDatabaseName("IX_ZugferdInvoices_InvoiceNumber_SellerTaxId");
+
+            // Decimal-Präzision explizit festlegen (behebt EF Core Warnung)
+            entity.Property(e => e.TotalAmount)
+                .HasColumnType("decimal(18,2)");
+
+            entity.Property(e => e.TaxAmount)
+                .HasColumnType("decimal(18,2)");
+        });
+    }
 }

DXApp.TemplateKitProject/Migrations/20260602114123_AddPerformanceIndexes.Designer.cs

@@ -0,0 +1,91 @@
+// <auto-generated />
+using System;
+using DXApp.TemplateKitProject.Data;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Infrastructure;
+using Microsoft.EntityFrameworkCore.Metadata;
+using Microsoft.EntityFrameworkCore.Migrations;
+using Microsoft.EntityFrameworkCore.Storage.ValueConversion;
+
+#nullable disable
+
+namespace DXApp.TemplateKitProject.Migrations
+{
+    [DbContext(typeof(AppDbContext))]
+    [Migration("20260602114123_AddPerformanceIndexes")]
+    partial class AddPerformanceIndexes
+    {
+        /// <inheritdoc />
+        protected override void BuildTargetModel(ModelBuilder modelBuilder)
+        {
+#pragma warning disable 612, 618
+            modelBuilder
+                .HasAnnotation("ProductVersion", "8.0.8")
+                .HasAnnotation("Relational:MaxIdentifierLength", 128);
+
+            SqlServerModelBuilderExtensions.UseIdentityColumns(modelBuilder);
+
+            modelBuilder.Entity("DXApp.TemplateKitProject.Models.ZugferdInvoice", b =>
+                {
+                    b.Property<int>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("int");
+
+                    SqlServerPropertyBuilderExtensions.UseIdentityColumn(b.Property<int>("Id"));
+
+                    b.Property<string>("BuyerName")
+                        .HasColumnType("nvarchar(max)");
+
+                    b.Property<string>("CurrencyCode")
+                        .HasColumnType("nvarchar(max)");
+
+                    b.Property<string>("GuidelineId")
+                        .HasColumnType("nvarchar(max)");
+
+                    b.Property<string>("Iban")
+                        .HasColumnType("nvarchar(max)");
+
+                    b.Property<DateTime>("ImportedAt")
+                        .HasColumnType("datetime2");
+
+                    b.Property<DateTime>("InvoiceDate")
+                        .HasColumnType("datetime2");
+
+                    b.Property<string>("InvoiceNumber")
+                        .HasColumnType("nvarchar(450)");
+
+                    b.Property<string>("RawXml")
+                        .HasColumnType("nvarchar(max)");
+
+                    b.Property<string>("ResultFilePath")
+                        .HasColumnType("nvarchar(max)");
+
+                    b.Property<string>("SellerName")
+                        .HasColumnType("nvarchar(max)");
+
+                    b.Property<string>("SellerTaxId")
+                        .HasColumnType("nvarchar(450)");
+
+                    b.Property<string>("SourceType")
+                        .HasColumnType("nvarchar(max)");
+
+                    b.Property<decimal>("TaxAmount")
+                        .HasColumnType("decimal(18,2)");
+
+                    b.Property<decimal>("TotalAmount")
+                        .HasColumnType("decimal(18,2)");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("ImportedAt")
+                        .HasDatabaseName("IX_ZugferdInvoices_ImportedAt");
+
+                    b.HasIndex("InvoiceNumber", "SellerTaxId")
+                        .HasDatabaseName("IX_ZugferdInvoices_InvoiceNumber_SellerTaxId");
+
+                    b.ToTable("ZugferdInvoices");
+                });
+#pragma warning restore 612, 618
+        }
+    }
+}

DXApp.TemplateKitProject/Migrations/20260602114123_AddPerformanceIndexes.cs

@@ -0,0 +1,72 @@
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace DXApp.TemplateKitProject.Migrations
+{
+    /// <inheritdoc />
+    public partial class AddPerformanceIndexes : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.AlterColumn<string>(
+                name: "SellerTaxId",
+                table: "ZugferdInvoices",
+                type: "nvarchar(450)",
+                nullable: true,
+                oldClrType: typeof(string),
+                oldType: "nvarchar(max)",
+                oldNullable: true);
+
+            migrationBuilder.AlterColumn<string>(
+                name: "InvoiceNumber",
+                table: "ZugferdInvoices",
+                type: "nvarchar(450)",
+                nullable: true,
+                oldClrType: typeof(string),
+                oldType: "nvarchar(max)",
+                oldNullable: true);
+
+            migrationBuilder.CreateIndex(
+                name: "IX_ZugferdInvoices_ImportedAt",
+                table: "ZugferdInvoices",
+                column: "ImportedAt");
+
+            migrationBuilder.CreateIndex(
+                name: "IX_ZugferdInvoices_InvoiceNumber_SellerTaxId",
+                table: "ZugferdInvoices",
+                columns: new[] { "InvoiceNumber", "SellerTaxId" });
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropIndex(
+                name: "IX_ZugferdInvoices_ImportedAt",
+                table: "ZugferdInvoices");
+
+            migrationBuilder.DropIndex(
+                name: "IX_ZugferdInvoices_InvoiceNumber_SellerTaxId",
+                table: "ZugferdInvoices");
+
+            migrationBuilder.AlterColumn<string>(
+                name: "SellerTaxId",
+                table: "ZugferdInvoices",
+                type: "nvarchar(max)",
+                nullable: true,
+                oldClrType: typeof(string),
+                oldType: "nvarchar(450)",
+                oldNullable: true);
+
+            migrationBuilder.AlterColumn<string>(
+                name: "InvoiceNumber",
+                table: "ZugferdInvoices",
+                type: "nvarchar(max)",
+                nullable: true,
+                oldClrType: typeof(string),
+                oldType: "nvarchar(450)",
+                oldNullable: true);
+        }
+    }
+}

DXApp.TemplateKitProject/Migrations/AppDbContextModelSnapshot.cs

@@ -49,7 +49,7 @@ namespace DXApp.TemplateKitProject.Migrations
                         .HasColumnType("datetime2");
 
                     b.Property<string>("InvoiceNumber")
-                        .HasColumnType("nvarchar(max)");
+                        .HasColumnType("nvarchar(450)");
 
                     b.Property<string>("RawXml")
                         .HasColumnType("nvarchar(max)");
@@ -61,7 +61,7 @@ namespace DXApp.TemplateKitProject.Migrations
                         .HasColumnType("nvarchar(max)");
 
                     b.Property<string>("SellerTaxId")
-                        .HasColumnType("nvarchar(max)");
+                        .HasColumnType("nvarchar(450)");
 
                     b.Property<string>("SourceType")
                         .HasColumnType("nvarchar(max)");
@@ -74,6 +74,12 @@ namespace DXApp.TemplateKitProject.Migrations
 
                     b.HasKey("Id");
 
+                    b.HasIndex("ImportedAt")
+                        .HasDatabaseName("IX_ZugferdInvoices_ImportedAt");
+
+                    b.HasIndex("InvoiceNumber", "SellerTaxId")
+                        .HasDatabaseName("IX_ZugferdInvoices_InvoiceNumber_SellerTaxId");
+
                     b.ToTable("ZugferdInvoices");
                 });
 #pragma warning restore 612, 618

DXApp.TemplateKitProject/Models/ZugferdInvoiceListDto.cs

@@ -0,0 +1,22 @@
+namespace DXApp.TemplateKitProject.Models;
+
+/// <summary>
+/// Lightweight DTO für die Rechnungsliste (ohne RawXml für bessere Performance)
+/// </summary>
+public class ZugferdInvoiceListDto
+{
+    public int Id { get; set; }
+    public string InvoiceNumber { get; set; } = string.Empty;
+    public DateTime InvoiceDate { get; set; }
+    public string SellerName { get; set; } = string.Empty;
+    public string SellerTaxId { get; set; } = string.Empty;
+    public string BuyerName { get; set; } = string.Empty;
+    public decimal TotalAmount { get; set; }
+    public decimal TaxAmount { get; set; }
+    public string CurrencyCode { get; set; } = string.Empty;
+    public string Iban { get; set; } = string.Empty;
+    public DateTime ImportedAt { get; set; }
+    public string SourceType { get; set; } = string.Empty;
+    public string ResultFilePath { get; set; } = string.Empty;
+    public string GuidelineId { get; set; } = string.Empty;
+}

DXApp.TemplateKitProject/Pages/Invoices/Index.cshtml

@@ -12,7 +12,7 @@
 }
 else
 {
-    @(Html.DevExtreme().DataGrid<DXApp.TemplateKitProject.Models.ZugferdInvoice>()
+    @(Html.DevExtreme().DataGrid<DXApp.TemplateKitProject.Models.ZugferdInvoiceListDto>()
         .DataSource(Model.Invoices)
         .KeyExpr("Id")
         .ShowBorders(true)

DXApp.TemplateKitProject/Pages/Invoices/Index.cshtml.cs

@@ -7,12 +7,30 @@ namespace DXApp.TemplateKitProject.Pages.Invoices;
 
 public class IndexModel(AppDbContext db) : PageModel
 {
-    public List<ZugferdInvoice> Invoices { get; private set; } = [];
+    public List<ZugferdInvoiceListDto> Invoices { get; private set; } = [];
 
     public async Task OnGetAsync()
     {
         Invoices = await db.ZugferdInvoices
             .OrderByDescending(i => i.ImportedAt)
+            .Select(i => new ZugferdInvoiceListDto
+            {
+                Id = i.Id,
+                InvoiceNumber = i.InvoiceNumber,
+                InvoiceDate = i.InvoiceDate,
+                SellerName = i.SellerName,
+                SellerTaxId = i.SellerTaxId,
+                BuyerName = i.BuyerName,
+                TotalAmount = i.TotalAmount,
+                TaxAmount = i.TaxAmount,
+                CurrencyCode = i.CurrencyCode,
+                Iban = i.Iban,
+                ImportedAt = i.ImportedAt,
+                SourceType = i.SourceType,
+                ResultFilePath = i.ResultFilePath,
+                GuidelineId = i.GuidelineId
+                // RawXml wird NICHT geladen ? Performance-Optimierung!
+            })
             .ToListAsync();
     }
 }