不需要的小数截断

Question

我的模特：

public class Product
{
    ...
        public decimal Fineness { get; set; }
    ...
}

为数据库播种：

new List<Product>
        {
            new Product { ..., Fineness = 0.757M, ... },
            new Product { ..., Fineness = 0.674M, ... },
            new Product { ..., Fineness = 0.475M, ... }
        }.ForEach(p => context.Products.Add(p));

查询数据库以测试播种：

var products = db.Products.ToList();
foreach (var p in products)
{
    S.D.Debug.WriteLine("ProductList: {0}, {1}", p.Name, p.Fineness);
}

控制台输出：

ProductList: Test Product, 0.75 
ProductList: Test Product, 0.67 
ProductList: Test Product, 0.47    

我是在做傻事还是什么？？？所有内容都被截断到小数点后 2 位。

解决方案 - 感谢 Patrick：

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    modelBuilder.Entity<Product>().Property(x => x.Fineness).HasPrecision(10, 5);
}

Answer 1

所以您已经定义了标准实体模型，这里是带有 id 和小数的产品，以及您需要的任何其他内容等。

public class Product
{
    public int Id { get; set; }
    public decimal Fineness { get; set; }
}

所以我定义了一个初始化程序，在这种情况下，数据库将删除并重新创建我提供的任何种子信息，每次我运行并执行我的应用程序时，都会调用它。

public class Initializer : DropCreateDatabaseAlways<Context>
{
    protected override void Seed(Context context)
    { 
        // note how I am specifying it here as 4 digits after the decimal point
        // and for the second one, 3 digits
        // this is where EF precision must be configured so you can expect
        // the values you tell EF to save to the db
        context.Products.Add(new Product() {Id = 1, Fineness = 145.2442m});
        context.Products.Add(new Product() {Id = 2, Fineness = 12.341m});
    }
}

public class Context : DbContext
{
    public IDbSet<Product> Products { get; set; }

    public Context()
    {
        // I always explicitly define how my EF should run, but this is not needed for the answer I am providing you
        Configuration.AutoDetectChangesEnabled = true;
        Configuration.ProxyCreationEnabled = true;
        Configuration.LazyLoadingEnabled = true;
        Configuration.ValidateOnSaveEnabled = true;
    }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        // so here, I am override the model configuration which is what 
        // EF can use in order to set-up the behaviour of how everything 
        // is configured in the database, from associations between
        // multiple entities and property validation, Null-able, Precision, required fields etc
        modelBuilder.Configurations.Add(new ProductConfiguration());
    }
}

public class ProductConfiguration : EntityTypeConfiguration<Product>
{
    public ProductConfiguration()
    {
        ToTable("Product");
        HasKey(x => x.Id).Property(x => x.Id).HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);

        // HAS PRECISION. 
        // Enforces how the value is to be stored in the database
        // Here you can see I set a scale of 3, that's 3 digits after
        // the decimal. Notice how in my seed method, I gave a product 4 digits!
        // That means it will NOT save the product with the other trailing digits.
        Property(x => x.Fineness).HasPrecision(precision: 10, scale: 3);
    }
}

使用 SQL Server 对象资源管理器，我可以查看我制作的 localdb 示例产品，以了解 EF 如何配置我的数据库。

[TestFixture]
public class Tests
{
    [Test]
    public void Test()
    {
        Database.SetInitializer(new Initializer());

        using (var ctx = new Context())
        {
            // assert our findings that it is indeed not what we actually specified in the seed method, because of our Entity configuration with HasPrecision.
            Product product1 = ctx.Products.Find(1);
            Assert.AreEqual(145.244m, product1.Fineness);

            Product product2 = ctx.Products.Find(2);
            Assert.AreEqual(12.341m, product2.Fineness);
        }         
    }
}

所以我们需要确保数据库知道它应该如何存储我们的十进制值，通过使用实体框架的模型构建器配置来配置我们的实体，通过使用FluentApi，我们可以通过EntityTypeConfiguration<T> 设置属性特征.

Answer 2

你不需要EntityTypeConfiguration，你可以简单地这样做：

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    modelBuilder.Entity<Product>().Property(x => x.Fineness).HasPrecision(10, 3);

    base.OnModelCreating(modelBuilder);
}

如果您想更改每个 decimal 的精度和比例，您可以这样做：

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    modelBuilder.Conventions.Remove<DecimalPropertyConvention>();
    modelBuilder.Conventions.Add(new DecimalPropertyConvention(10, 3));
}

如果您希望 Decimal (10,3) 将 Fineness = 0.7577m 舍入为 0.758 而不是将 0.757 保存到数据库中，请查看下面的答案。它还解释了为什么 Entity Framework 6.X 默认截断十进制值而不是四舍五入。

https://stackoverflow.com/a/57095584/3850405

Answer 3

这是很好的tutorial 用于格式化十进制数字

D.Debug.WriteLine("ProductList: {0}, {1:0.000}", p.Name, p.Fineness);

// just two decimal places
String.Format("{0:0.00}", 123.4567);      // "123.46"
String.Format("{0:0.00}", 123.4);         // "123.40"
String.Format("{0:0.00}", 123.0);         // "123.00"

// max. two decimal places
String.Format("{0:0.##}", 123.4567);      // "123.46"
String.Format("{0:0.##}", 123.4);         // "123.4"
String.Format("{0:0.##}", 123.0);         // "123"

// at least two digits before decimal point
String.Format("{0:00.0}", 123.4567);      // "123.5"
String.Format("{0:00.0}", 23.4567);       // "23.5"
String.Format("{0:00.0}", 3.4567);        // "03.5"
String.Format("{0:00.0}", -3.4567);       // "-03.5"

//Zero formatting
String.Format("{0:0.0}", 0.0);            // "0.0"
String.Format("{0:0.#}", 0.0);            // "0"
String.Format("{0:#.0}", 0.0);            // ".0"
String.Format("{0:#.#}", 0.0);            // ""