利用dynamic简化数据库的访问

今天写了一个数据库的帮助类，代码如下。

 1 public static class DbEx
 2 {
 3     public static dynamic ReadToObject(this IDataReader reader)
 4     {
 5         var obj = new DbObject();
 6 
 7         for (int i = 0; i < reader.FieldCount; i++)
 8         {
 9             obj[reader.GetName(i)] = new DbField()
10             {
11                 DbData = reader[i]
12             };
13         }
14 
15         return obj;
16     }
17 
18     public class DbObject : DynamicObject
19     {
20         //自己实现一个，不用ExpandoObject， 以支持无视大小写读取
21         public override bool TryGetMember(GetMemberBinder binder, out object result)
22         {
23             result = this[binder.Name];
24             return true;
25         }
26 
27         Dictionary<string, object> _values = new Dictionary<string, object>(StringComparer.CurrentCultureIgnoreCase);
28 
29         public object this[string index]
30         {
31             get => _values[index];
32             set => _values[index] = value;
33         }
34     }
35 
36     public class DbField
37     {
38         public object DbData { get; set; }
39 
40         public T Value<T>()
41         {
42             return (T)Convert.ChangeType(DbData, typeof(T));
43         }
44 
45         public static implicit operator string(DbField data) => data.Value<string>();
46         public static implicit operator int(DbField data) => data.Value<int>();
47         public static implicit operator DateTime(DbField data) => data.Value<DateTime>();
48         public static implicit operator double(DbField data) => data.Value<double>();
49         public static implicit operator bool(DbField data) => data.Value<bool>();
50     }
51 }

View Code

简单的来讲，可以把如下代码

GpsData parse(IDataReader reader)
{
    return new GpsData()
    {
        IsValid = (bool)reader["IsValid"],
        Location = new Location ()
        {
            Lon = (double)reader["Lon"],
            Lat = (double)reader["Lat"],
        },
        Angle = (double)reader["Angle"],
        Speed = (double)reader["Speed"]),
        UpdateTime = (double)reader["Speed"]),
    };
}

转换为如下形式

GpsData parse(IDataReader reader)
{
    var obj = reader.ReadToObject();
    var state = new GpsData()
    {
        IsValid = obj.IsValid,
        Location = new Location()
        {
            Lon = obj.Lon,
            Lat = obj.Lat,
        },
        Angle = obj.Angle,
        Speed = obj.Speed,
        UpdateTime = obj.UpdateTime,
    };
    return state;
}

主要还是利用dynamic的特性，转换成这样的好处有：

以属性的方式替换下标方式读取，更加间接直观
属性的方式读取变量时不分大小写
支持自动类型转换，例如，如果数据库里的类型是int型，而目标是string型，会进行自动类型转换
自动识别目标类型，不需要显示强制类型转换，更加简洁