设置EntityFramework中decimal类型数据精度问题(EF默认将只会保留到2为精度)

原文:设置EntityFramework中decimal类型数据精度

EF中默认的decimal数据精度为两位数，当我们数据库设置的精度大于2时，EF将只会保留到2为精度。

e.g.  2.19990将会被保存为2.20

1.解决方案一是网上找到常见的方法为重写DbContext的OnModelCreating方法：

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{            
　　modelBuilder.Entity<Product>().Property(x => x.Price).HasPrecision(18, 5);
}

但如果数据表多或者Decimal类型字段多的话，用OnModelCreating的方法将会变得相当冗余，而且不便管理。

2.解决方案二是我推荐使用Attribute属性标签进行设置，在Entity Model class中decimal的字段上方直接添加自定义拓展的属性标签即可。

调用:

其中 [DecimalPrecision(18, 5)]即是我们自定义的精度Attribute

具体实现代码如下：

 /// <summary>
     /// <para>自定义Decimal类型的精度属性</para>
     /// </summary>
     [AttributeUsage(AttributeTargets.Property, Inherited = false, AllowMultiple = false)]
     public   class DecimalPrecisionAttribute : Attribute
     {
 
         #region Field
         private byte _precision = 18;
         public byte _scale = 5;
         #endregion
 
         #region Construct
         /// <summary>
         /// <para>自定义Decimal类型的精确度属性</para>
         /// </summary>
         /// <param name="precision">precision
         /// <para>精度（默认18）</para></param>
         /// <param name="scale">scale
         /// <para>小数位数（默认5）</para></param>
         public DecimalPrecisionAttribute(byte precision = 18, byte scale = 5)
         {
             Precision = precision;
             Scale = scale;
         } 
         #endregion
         
         #region Property
         /// <summary>
         /// 精确度（默认18）
         /// </summary>
         public byte Precision
         {
             get { return this._precision; }
             set { this._precision = value; }
         }
 
         /// <summary>
         /// 保留位数（默认5）
         /// </summary>
         public byte Scale
         {
             get { return this._scale; }
             set { this._scale = value; }
         } 
         #endregion
     }

  /// <summary>
    /// 用于modelBuilder全局设置自定义精度属性
    /// </summary>
    public class DecimalPrecisionAttributeConvention
        : PrimitivePropertyAttributeConfigurationConvention<DecimalPrecisionAttribute>
    {
        public override void Apply(ConventionPrimitivePropertyConfiguration configuration, DecimalPrecisionAttribute attribute)
        {
            if (attribute.Precision< 1 || attribute.Precision> 38)
            {
                throw new InvalidOperationException("Precision must be between 1 and 38.");
            }
            if (attribute.Scale > attribute.Precision)
            {
                throw new InvalidOperationException("Scale must be between 0 and the Precision value.");
            }
            configuration.HasPrecision(attribute.Precision, attribute.Scale);
        }
    }

再在DbContext重写OnModelCreating，添加自定义的DecimalPrecisionAttributeConvention即可以方便地任意添加需要精度控制的字段。

    public class Project_DbContext : DbContext
    {
        public Project_DbContext() : base("DefaultConnection") { }

        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            modelBuilder.Conventions.Add(new DecimalPrecisionAttributeConvention());
            base.OnModelCreating(modelBuilder);
        }

    }

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