c# Entity framework foreign key - entity-framework

Question

I'm new here and hope I'll get an answer - I'm searching the internet since two days ...
It's the first time I use the entity framewort in a Windows 10 UWP. I have to classes which are the objects for my database. In one object I use a property with the type of the other.
If I'll try to add a record I'll get a error.
public class budgetcontext : DbContext
{
private string myDB = "Filename=budget_4.db";
public DbSet<category> Categories { get; set; }
public DbSet<transaction> Transactions { get; set; }
public budgetcontext()
{
this.Database.Migrate();
}
protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
optionsBuilder.UseSqlite(myDB);
}
}
public class category
{
private string myGuid = Guid.NewGuid().ToString();
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int CategoryId { get; set; }
public string Name { get; set; }
public double BudgetDaily { get; set; }
public double BudgetWeekly { get; set; }
public double BudgetMonthly { get; set; }
public double BudgetYearly { get; set; }
public string CategoryGuid
{
get
{
return myGuid;
}
}
}
public class transaction
{
private string myGuid = Guid.NewGuid().ToString();
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public Int64 TransactionId { get; set; }
public string Text { get; set; }
public category Category { get; set; }
public DateTime TransDateTime { get; set; }
public double Amount { get; set; }
}
If I try to insert a record of the type transaction to the database I'll get the error:
{"SQLite Error 19: 'UNIQUE constraint failed: Categories.CategoryId'."}
The code to insert the object is:
budget_sqlite.category c = cbCategory.SelectedItem as budget_sqlite.category; //Object is selected in a Combo
using (var db = new budget_sqlite.budgetcontext())
{
t.Text = this.txtText.Text;
t.Category = c;
t.TransDateTime = new DateTime(dpDate.Date.Year, dpDate.Date.Month, dpDate.Date.Day, tpTime.Time.Hours, tpTime.Time.Minutes, tpTime.Time.Seconds);
double.TryParse(txtAmount.Text, out value);
if (RBOut.IsChecked == true)
{
value = value * -1;
}
t.Amount = value;
if (t.TransactionId == 0)
{
db.Transactions.Add(t);
}
db.SaveChanges();
}
Here are the migrations:
[DbContext(typeof(budgetcontext))]
partial class budgetcontextModelSnapshot : ModelSnapshot
{
protected override void BuildModel(ModelBuilder modelBuilder)
{
modelBuilder
.HasAnnotation("ProductVersion", "1.1.0-rtm-22752");
modelBuilder.Entity("budget_sqlite.category", b =>
{
b.Property<int>("CategoryId")
.ValueGeneratedOnAdd();
b.Property<double>("BudgetDaily");
b.Property<double>("BudgetMonthly");
b.Property<double>("BudgetWeekly");
b.Property<double>("BudgetYearly");
b.Property<string>("Name");
b.HasKey("CategoryId");
b.ToTable("Categories");
});
modelBuilder.Entity("budget_sqlite.transaction", b =>
{
b.Property<long>("TransactionId")
.ValueGeneratedOnAdd();
b.Property<double>("Amount");
b.Property<int?>("CategoryId");
b.Property<string>("Text");
b.Property<DateTime>("TransDateTime");
b.HasKey("TransactionId");
b.HasIndex("CategoryId");
b.ToTable("Transactions");
});
modelBuilder.Entity("budget_sqlite.transaction", b =>
{
b.HasOne("budget_sqlite.category", "Category")
.WithMany()
.HasForeignKey("CategoryId");
});
}
}
public partial class V0001 : Migration
{
protected override void Up(MigrationBuilder migrationBuilder)
{
migrationBuilder.CreateTable(
name: "Categories",
columns: table => new
{
CategoryId = table.Column<int>(nullable: false)
.Annotation("Sqlite:Autoincrement", true),
BudgetDaily = table.Column<double>(nullable: false),
BudgetMonthly = table.Column<double>(nullable: false),
BudgetWeekly = table.Column<double>(nullable: false),
BudgetYearly = table.Column<double>(nullable: false),
Name = table.Column<string>(nullable: true)
},
constraints: table =>
{
table.PrimaryKey("PK_Categories", x => x.CategoryId);
});
migrationBuilder.CreateTable(
name: "Transactions",
columns: table => new
{
TransactionId = table.Column<long>(nullable: false)
.Annotation("Sqlite:Autoincrement", true),
Amount = table.Column<double>(nullable: false),
CategoryId = table.Column<int>(nullable: true),
Text = table.Column<string>(nullable: true),
TransDateTime = table.Column<DateTime>(nullable: false)
},
constraints: table =>
{
table.PrimaryKey("PK_Transactions", x => x.TransactionId);
table.ForeignKey(
name: "FK_Transactions_Categories_CategoryId",
column: x => x.CategoryId,
principalTable: "Categories",
principalColumn: "CategoryId",
onDelete: ReferentialAction.Restrict);
});
migrationBuilder.CreateIndex(
name: "IX_Transactions_CategoryId",
table: "Transactions",
column: "CategoryId");
}
protected override void Down(MigrationBuilder migrationBuilder)
{
migrationBuilder.DropTable(
name: "Transactions");
migrationBuilder.DropTable(
name: "Categories");
}
}
Thank you very much for your help.