diff --git a/Data.SeaHavenIndustries/Auth/ApplicationDbContext.cs b/Data.SeaHavenIndustries/Auth/ApplicationDbContext.cs
index 7c45127..1cea35d 100644
--- a/Data.SeaHavenIndustries/Auth/ApplicationDbContext.cs
+++ b/Data.SeaHavenIndustries/Auth/ApplicationDbContext.cs
@@ -61,6 +61,15 @@ namespace Data.SeaHavenIndustries
                 .HasIndex(w => new { w.LifecycleStatus, w.ScheduledDate })
                 .HasFilter("[istemplate] = 0");
 
+            builder.Entity<WorkOrder>()
+                .Property(w => w.ExternalWorkOrderId)
+                .HasMaxLength(450);
+
+            builder.Entity<WorkOrder>()
+                .HasIndex(w => w.ExternalWorkOrderId)
+                .IsUnique()
+                .HasFilter("[ExternalWorkOrderId] IS NOT NULL AND [ExternalWorkOrderId] <> ''");
+
             builder.Entity<Dispatch>()
                 .Property(d => d.RowVersion)
                 .IsRowVersion();
diff --git a/Data.SeaHavenIndustries/Migrations/20260713120000_Phase7_ExternalWorkOrderIdUnique.cs b/Data.SeaHavenIndustries/Migrations/20260713120000_Phase7_ExternalWorkOrderIdUnique.cs
new file mode 100644
index 0000000..291a952
--- /dev/null
+++ b/Data.SeaHavenIndustries/Migrations/20260713120000_Phase7_ExternalWorkOrderIdUnique.cs
@@ -0,0 +1,49 @@
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace Data.SeaHavenIndustries.Migrations
+{
+    /// <inheritdoc />
+    public partial class Phase7_ExternalWorkOrderIdUnique : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.AlterColumn<string>(
+                name: "ExternalWorkOrderId",
+                table: "workOrders",
+                type: "nvarchar(450)",
+                maxLength: 450,
+                nullable: true,
+                oldClrType: typeof(string),
+                oldType: "nvarchar(max)",
+                oldNullable: true);
+
+            migrationBuilder.CreateIndex(
+                name: "IX_workOrders_ExternalWorkOrderId",
+                table: "workOrders",
+                column: "ExternalWorkOrderId",
+                unique: true,
+                filter: "[ExternalWorkOrderId] IS NOT NULL AND [ExternalWorkOrderId] <> ''");
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropIndex(
+                name: "IX_workOrders_ExternalWorkOrderId",
+                table: "workOrders");
+
+            migrationBuilder.AlterColumn<string>(
+                name: "ExternalWorkOrderId",
+                table: "workOrders",
+                type: "nvarchar(max)",
+                nullable: true,
+                oldClrType: typeof(string),
+                oldType: "nvarchar(450)",
+                oldMaxLength: 450,
+                oldNullable: true);
+        }
+    }
+}
diff --git a/Data.SeaHavenIndustries/Migrations/ApplicationDbContextModelSnapshot.cs b/Data.SeaHavenIndustries/Migrations/ApplicationDbContextModelSnapshot.cs
index 2245ad2..d97ab9b 100644
--- a/Data.SeaHavenIndustries/Migrations/ApplicationDbContextModelSnapshot.cs
+++ b/Data.SeaHavenIndustries/Migrations/ApplicationDbContextModelSnapshot.cs
@@ -1960,7 +1960,8 @@ namespace Data.SeaHavenIndustries.Migrations
                         .HasColumnType("datetime2");
 
                     b.Property<string>("ExternalWorkOrderId")
-                        .HasColumnType("nvarchar(max)");
+                        .HasMaxLength(450)
+                        .HasColumnType("nvarchar(450)");
 
                     b.Property<string>("InternalWONumber")
                         .HasColumnType("nvarchar(max)");
@@ -2088,6 +2089,10 @@ namespace Data.SeaHavenIndustries.Migrations
 
                     b.HasIndex("AssignTo", "ScheduledDate");
 
+                    b.HasIndex("ExternalWorkOrderId")
+                        .IsUnique()
+                        .HasFilter("[ExternalWorkOrderId] IS NOT NULL AND [ExternalWorkOrderId] <> ''");
+
                     b.HasIndex("InternalWONumber")
                         .HasFilter("[istemplate] = 0");