Entity framework core creating additional table columns

Question

I am trying to migrate a simple table but ef-core is creating additional columns which i haven't specified

Here is my model which i used to create a sql table

public class Transaction
{
        [Key]
        public int Id { get; set; }

        [Required]
        public decimal Amount { get; set; }

        [Required]
        public DateTime DateTimeCreated { get; set; } = DateTime.UtcNow;

        [MaxLength(1024)]
        public string Description { get; set; }

        [Required]
        public int CategoryId { get; set; }

        public virtual Category Category { get; set; }

        [Required]
        public int UserId { get; set; }

        public virtual User User { get; set; }
    }

EF-Core is creating the following table.

How to stop EF-Core from generating CategoryName and CategoryCashFlowId columns

migrationBuilder.CreateTable(
                name: "Transactions",
                columns: table => new
                {
                    Id = table.Column<int>(nullable: false)
                        .Annotation("SqlServer:Identity", "1, 1"),
                    Amount = table.Column<decimal>(nullable: false),
                    DateTimeCreated = table.Column<DateTime>(nullable: false),
                    Description = table.Column<string>(maxLength: 1024, nullable: true),
                    CategoryId = table.Column<int>(nullable: false),
                    CategoryName = table.Column<string>(nullable: false),
                    CategoryCashFlowId = table.Column<int>(nullable: false),
                    UserId = table.Column<int>(nullable: false)
                },
                constraints: table =>
                {
                    table.PrimaryKey("PK_Transactions", x => x.Id);
                    table.ForeignKey(
                        name: "FK_Transactions_Users_UserId",
                        column: x => x.UserId,
                        principalTable: "Users",
                        principalColumn: "Id",
                        onDelete: ReferentialAction.Cascade);
                    table.ForeignKey(
                        name: "FK_Transactions_Categories_CategoryName_CategoryCashFlowId",
                        columns: x => new { x.CategoryName, x.CategoryCashFlowId },
                        principalTable: "Categories",
                        principalColumns: new[] { "Name", "CashFlowId" },
                        onDelete: ReferentialAction.Cascade);
                });

Here is my fluent api code

protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            //base.OnModelCreating(modelBuilder);

            modelBuilder.Entity<User>().HasIndex("Username").IsUnique();
            modelBuilder.Entity<Category>().HasKey(c => new { c.Name, c.CashFlowId });

            modelBuilder.Entity<Common.Models.CashFlow>().HasData(
                new CashFlow { Id = 1, Name = "Income" },
                new CashFlow { Id = 2, Name = "Expense" }
            );

            modelBuilder.Entity<Common.Models.Category>().HasData(
                new Category { Id = 1, Name = "Food and Drinks", CashFlowId = 2 },
                new Category { Id = 2, Name = "Travel", CashFlowId = 2 },
                new Category { Id = 3, Name = "Salary", CashFlowId = 1 }
            );
        }

Edit 1: Category Model

public class Category
{
        public int Id { get; set; }

        /// <summary>
        /// <remarks> Is Indexed with CashflowId </remarks>
        /// </summary>
        [MaxLength(32)]
        [Required]
        public string Name { get; set; }

        [Required]
        public int CashFlowId { get; set; }

        public CashFlow CashFlow { get; set; }

}

Edit 2: Added CashFlow model

public class CashFlow
{
        [Key]
        public int Id { get; set; }

        [MaxLength(32)]
        public string Name { get; set; }
}

Edit 3: Posted my DbContext

public class AppDbContext : DbContext
    {

        public DbSet<User> Users { get; set; }

        public DbSet<Common.Models.Transaction> Transactions { get; set; }

        public DbSet<Category> Categories { get; set; }

        public DbSet<CashFlow> CashFlows { get; set; }

        public AppDbContext(DbContextOptions<AppDbContext> dbContextOptions) : base(dbContextOptions)
        {
            ChangeTracker.QueryTrackingBehavior = QueryTrackingBehavior.NoTracking;
        }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            //base.OnModelCreating(modelBuilder);

            modelBuilder.Entity<User>().HasIndex("Username").IsUnique();
            modelBuilder.Entity<Category>().HasKey(c => new { c.Name, c.CashFlowId });

            modelBuilder.Entity<Common.Models.CashFlow>().HasData(
                new CashFlow { Id = 1, Name = "Income" },
                new CashFlow { Id = 2, Name = "Expense" }
            );

            modelBuilder.Entity<Common.Models.Category>().HasData(
                new Category { Id = 1, Name = "Food and Drinks", CashFlowId = 2 },
                new Category { Id = 2, Name = "Travel", CashFlowId = 2 },
                new Category { Id = 3, Name = "Salary", CashFlowId = 1 }
            );
        }
    }

I don't understand why CategoryName and CategoryCashFlowId columns are getting created

Please help

Answer 1

CashFlow on Category should be virtual.

public virtual CashFlow CashFlow { get; set; }

Category should be

public class Category
{
        [Key]
        public int Id { get; set; }

        /// <summary>
        /// <remarks> Is Indexed with CashflowId </remarks>
        /// </summary>
        [MaxLength(32)]
        [Required]
        public string Name { get; set; }

        [Required]
        [Index("IX_NameCashFlowId", 1, IsUnique = true)]
        public int CashFlowId { get; set; }

        [Index("IX_NameCashFlowId", 1, IsUnique = true)]
        public CashFlow CashFlow { get; set; }

}

With this setup modelBuilder.Entity<Category>().HasKey is not needed.

Answer 2

I believe this is because your Transaction model has a reference (navigation property) to the Category model, along with a CategoryId. But it can't actually reference the Category model by the CategoryId because the Category model actually has a composite key of Name and CashFlowId. So Entity Framework adds these behind the scenes to reference it.

I think you can create an alternate key on Category using CategoryId and it would be referenced that way without creating the extra columns.

modelBuilder.Entity<Category>()
    .HasKey(c => new { c.Name, c.CashFlowId })
    .HasAlternateKey(c => c.CategoryId);

Reference: https://learn.microsoft.com/en-us/ef/core/modeling/alternate-keys

Answer 3

when u use this config for

modelBuilder.Entity<Category>().HasKey(c => new { c.Name, c.CashFlowId });

category table primary key is Name and CashFlowId and transaction table for relation must generate these columns.

Answer 4

why CategoryName and CategoryCashFlowId columns are getting created

With this line: modelBuilder.Entity<Category>().HasKey(c => new { c.Name, c.CashFlowId }); You are creating a composite key for table Category which cannot be an int.

In your Transaction object you are trying to map a key CategoryId for your Category as stated before your composite key cannot be an int nether a single property just by nature of composition. So at this point CategoryId is not a foreign key, it's just another property.

EF core is putting the two properties you used for the primary composite key of your Category object in to your Transaction object to be used as a foreign composite key.

You can resolve this by removing the composition.