Entity Framework Core– Avoid losing precision

When mapping a decimal type to a database through an ORM like EF Core, it is important to consider the precision. You don't want to lose data or end up with incorrect values because the maximum number of digits differs between the application and database.

If you don’t explicitly configure the store type, EF Core will give you a warning to avoid losing precision.

Imagine that we have the following Product class with a corresponding configuration:

	public class Product
	{
	public int Id { get; set;}
	public decimal UnitPrice{ get; set;}
	public Category Category { get; set;}
	}

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	internal class ProductMap : IEntityTypeConfiguration<Product>
	{
	public void Configure(EntityTypeBuilder<Product> builder)
	{
	builder.Property(x => x.Id).HasColumnName("ProductID");
	builder.Property(x=> x.UnitPrice);
	builder.HasOne(x=> x.Category)
	.WithMany(x=> x.Products)
	.HasForeignKey("CategoryID");
	}
	}

view raw ProductMap.cs hosted with ❤ by GitHub

If we try to use this Product class in our application, we get the following warning:

warn: SqlServerEventId.DecimalTypeDefaultWarning[30000] (Microsoft.EntityFrameworkCore.Model.Validation)

      No store type was specified for the decimal property 'UnitPrice' on entity type 'Product'. This will cause values to be silently truncated if they do not fit in the default precision and scale. Explicitly specify the SQL server column type that can accommodate all the values in 'OnModelCreating' using 'HasColumnType', specify precision and scale using 'HasPrecision', or configure a value converter using 'HasConversion'.

To fix this warning, we can set a specific store type:

	internal class ProductMap : IEntityTypeConfiguration<Product>
	{
	public void Configure(EntityTypeBuilder<Product> builder)
	{
	builder.Property(x => x.Id).HasColumnName("ProductID");
	builder.Property(x=> x.UnitPrice).HasColumnType("money");
	builder.HasOne(x=> x.Category)
	.WithMany(x=> x.Products)
	.HasForeignKey("CategoryID");
	}
	}

view raw ProductMap.cs hosted with ❤ by GitHub

Or explicitly set the precision:

	internal class ProductMap : IEntityTypeConfiguration<Product>
	{
	public void Configure(EntityTypeBuilder<Product> builder)
	{
	builder.Property(x => x.Id).HasColumnName("ProductID");
	builder.Property(x=> x.UnitPrice).HasPrecision(18,2);
	builder.HasOne(x=> x.Category)
	.WithMany(x=> x.Products)
	.HasForeignKey("CategoryID");
	}
	}

view raw ProductMap.cs hosted with ❤ by GitHub

More information

Entity Properties - EF Core | Microsoft Learn