設置EntityFramework中decimal類型數據精度

EF中預設的decimal數據精度為兩位數，當我們資料庫設置的精度大於2時，EF將只會保留到2為精度。

e.g.  2.1999將會被保存為2.20

網上找到常見的方法為重寫DbContext的OnModelCreating方法：

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{            
　　modelBuilder.Entity<Product>().Property(x => x.Price).HasPrecision(18, 4);
}

但如果數據表多或者Decimal類型欄位多的話，用OnModelCreating的方法將會變得相當冗餘，而且不便管理。

我推薦使用Attribute屬性標簽進行設置，在Entity Model class中decimal的欄位上方直接添加自定義拓展的屬性標簽即可。

e.g.

其中 [DecimalPrecision(18, 4)]即是我們自定義的精度Attribute

具體實現代碼如下：

 1     /// <summary>
 2     /// <para>自定義Decimal類型的精度屬性</para>
 3     /// </summary>
 4     [AttributeUsage(AttributeTargets.Property, Inherited = false, AllowMultiple = false)]
 5     public sealed class DecimalPrecisionAttribute : Attribute
 6     {
 7 
 8         #region Field
 9         private byte _precision = 18;
10         public byte _scale = 4;
11         #endregion
12 
13         #region Construct
14         /// <summary>
15         /// <para>自定義Decimal類型的精確度屬性</para>
16         /// </summary>
17         /// <param name="precision">precision
18         /// <para>精度（預設18）</para></param>
19         /// <param name="scale">scale
20         /// <para>小數位數（預設4）</para></param>
21         public DecimalPrecisionAttribute(byte precision = 18, byte scale = 4)
22         {
23             Precision = precision;
24             Scale = scale;
25         } 
26         #endregion
27         
28         #region Property
29         /// <summary>
30         /// 精確度（預設18）
31         /// </summary>
32         public byte Precision
33         {
34             get { return this._precision; }
35             set { this._precision = value; }
36         }
37 
38         /// <summary>
39         /// 保留位數（預設4）
40         /// </summary>
41         public byte Scale
42         {
43             get { return this._scale; }
44             set { this._scale = value; }
45         } 
46         #endregion
47     }
48 
49     /// <summary>
50     /// 用於modelBuilder全局設置自定義精度屬性
51     /// </summary>
52     public class DecimalPrecisionAttributeConvention
53         : PrimitivePropertyAttributeConfigurationConvention<DecimalPrecisionAttribute>
54     {
55         public override void Apply(ConventionPrimitivePropertyConfiguration configuration, DecimalPrecisionAttribute attribute)
56         {
57             if (attribute.Precision < 1 || attribute.Precision > 38)
58             {
59                 throw new InvalidOperationException("Precision must be between 1 and 38.");
60             }
61             if (attribute.Scale > attribute.Precision)
62             {
63                 throw new InvalidOperationException("Scale must be between 0 and the Precision value.");
64             }
65             configuration.HasPrecision(attribute.Precision, attribute.Scale);
66         }
67     }

再在DbContext重寫OnModelCreating，添加自定義的DecimalPrecisionAttributeConvention即可以方便地任意添加需要精度控制的欄位。

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

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

    }