How to use decimal precision and scale in EF Code First

In Entity Framework, when using the decimal data type, there's a default behavior where any values assigned are truncated to zero after the decimal point before storing in the database.

In Entity Framework, when using the decimal data type, there's a default behavior where any values assigned are truncated to zero after the decimal point before storing in the database, leading to issues with ef decimal precision.

For instance, if you try to save the value 0.37411 into a decimal column in C#, Entity Framework will truncate .37411 and store only 0 in the database column.

Even if your database column is defined with a higher precision and scale, such as decimal(18, 8), Entity Framework will still truncate any values under the decimal point before saving them. This means that precision beyond the integer part of the number is lost during the storage process.

How to use decimal data type in entity framework in c#

Suppose you have an entity called Product.

public class Product
{
    public int Id { get; set; }
    public string ProductName { get; set; }
    public decimal Price { get; set; }
}

Here, Price is of type decimal, which is appropriate for storing monetary values due to its precise decimal representation.

By default, Entity Framework will map the decimal property to an appropriate column type in your database.

To solve the problem of decimal precision and scale in Entity Framework, you can use HasPrecision() in OnModelCreating() method.

// c# decimal scale
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
      // Configure mappings
      modelBuilder.Entity<Product>()
          .Property(p => p.Price)
          .HasPrecision(18, 8); // specifying precision and scale

      // Optionally, other configurations for your entities
}

In this example, HasPrecision(18, 8) specifies that the Price property should have a precision of 18 digits in total, with 8 digits after the decimal point.

You can also use the Fluent API in your DbContext class's OnModelCreating method to customize the database mapping for decimal

// ef core decimal precision
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Product>()
        .Property(p => p.Price)
        .HasColumnType("decimal(18, 8)"); // Example: specifying decimal precision and scale
}

To solve the problem of decimal precision and scale in Entity Framework Core, you can add [Column(TypeName = "decimal(18, 8)")] annotation on deciaml property.

public class Product
{
    [Key]
    [Required]
    public int Id { get; set; }    
    
    public string ProductName { get; set; }    
    
    [Column(TypeName = "decimal(18, 8)")]
    public decimal Price { get; set; }
}

By following these steps, you can effectively use the Decimal data type with Entity Framework in your C# applications.