c# - 替代反射

Question

我对泛型和反射的经验非常少。我从以下示例中得出的假设是执行时间太长。有没有办法让我在不使用反射的情况下完成以下任务..

场景我正在研究一种通用的方法。它获取传递给它的类的实例，并根据所有属性生成 SqlParameters。以下是名为“Store”的泛型方法的代码，以及将 c# 类型转换为 DbType 的 SqlDbType 的另一种方法。

        List<SqlParameter> parameters = new List<SqlParameter>();
        public T Store<T>(T t)
        {
            Type type = t.GetType();
            PropertyInfo[] props = (t.GetType()).GetProperties();
            foreach (PropertyInfo p in props)
            {
                SqlParameter param = new SqlParameter();
                Type propType = p.PropertyType;
                if (propType.BaseType.Name.Equals("ValueType") || propType.BaseType.Name.Equals("Array"))
                {
                    param.SqlDbType = GetDBType(propType); //e.g. public bool enabled{get;set;} OR public byte[] img{get;set;}
                }
                else if (propType.BaseType.Name.Equals("Object"))
                {
                    if (propType.Name.Equals("String"))// for string values
                        param.SqlDbType = GetDBType(propType);
                    else
                    {
                        dynamic d = p.GetValue(t, null); // for referrences e.g. public ClassA obj{get;set;}
                        Store<dynamic>(d);
                    }
                }
                param.ParameterName = p.Name;
                parameters.Add(param);
            }
            return t;
        }



        // mehthod for getting the DbType OR SqlDbType from the type...
        private SqlDbType GetDBType(System.Type type)
        {
            SqlParameter param;
            System.ComponentModel.TypeConverter tc;
            param = new SqlParameter();
            tc = System.ComponentModel.TypeDescriptor.GetConverter(param.DbType);
            if (tc.CanConvertFrom(type))
            {
                param.DbType = (DbType)tc.ConvertFrom(type.Name);
            }
            else
            {
                // try to forcefully convert
                try
                {
                    param.DbType = (DbType)tc.ConvertFrom(type.Name);
                }
                catch (Exception e)
                {
                    switch (type.Name)
                    {
                        case "Char":
                            param.SqlDbType = SqlDbType.Char;
                            break;
                        case "SByte":
                            param.SqlDbType = SqlDbType.SmallInt;
                            break;
                        case "UInt16":
                            param.SqlDbType = SqlDbType.SmallInt;
                            break;
                        case "UInt32":
                            param.SqlDbType = SqlDbType.Int;
                            break;
                        case "UInt64":
                            param.SqlDbType = SqlDbType.Decimal;
                            break;
                        case "Byte[]":
                            param.SqlDbType = SqlDbType.Binary;
                            break;
                    }
                }
            }
            return param.SqlDbType;
        }

要调用我的方法，假设我有以下 2 个类

public class clsParent
{
    public int pID { get; set; }
    public byte[] pImage { get; set; }
    public string pName { get; set; }
}

and

public class clsChild
{
    public decimal childId { get; set; }
    public string childName { get; set; }
    public clsParent parent { get; set; }
}

and this is a call 


clsParent p = new clsParent();
p.pID = 101;
p.pImage = new byte[1000];
p.pName = "John";
clsChild c = new clsChild();
c.childId = 1;
c.childName = "a";
c.parent = p;

Store<clsChild>(c);

Answer 1

如果你想摆脱反射，你可以在下面的代码中找到灵感。

在这里，所有对要存储在数据库中的对象的访问以及 sql 属性值分配都由根据数据类型构建的运行时编译表达式处理。

保存值的表假定为 test并且假定字段名称与属性值相同。

对于每个属性一个 Mapping<T>被构造。它将持有 FieldName包含数据库字段，SqlParameter这应该被正确插入到 SQL INSERT语句(main 中的示例)最后 if 包含已编译的操作，它可以采用输入的实例 T对象并将值赋给 SqlParameters属性(property)Value .这些映射的集合的构造在 Mapper<T> 中完成类(class)。内联代码以供解释。

最后 main方法展示了如何将这些东西绑定(bind)在一起。

using System;
using System.Collections.Generic;
using System.Data.SqlClient;
using System.Diagnostics;
using System.Linq;
using System.Linq.Expressions;

namespace ExpTest
{
    class Program
    {
        public class Mapping<T>
        {
            public Mapping(string fieldname, SqlParameter sqlParameter, Action<T, SqlParameter> assigner)
            {
                FieldName = fieldname;
                SqlParameter = sqlParameter;
                SqlParameterAssignment = assigner;
            }
            public string FieldName { get; private set; }
            public SqlParameter SqlParameter { get; private set; }
            public Action<T, SqlParameter> SqlParameterAssignment { get; private set; }
        }

        public class Mapper<T>
        {
            public IEnumerable<Mapping<T>> GetMappingElements()
            {
                foreach (var reflectionProperty in typeof(T).GetProperties())
                {
                    // Input parameters to the created assignment action
                    var accessor = Expression.Parameter(typeof(T), "input");
                    var sqlParmAccessor = Expression.Parameter(typeof(SqlParameter), "sqlParm");

                    // Access the property (compiled later, but use reflection to locate property)
                    var property = Expression.Property(accessor, reflectionProperty);

                    // Cast the property to ensure it is assignable to SqlProperty.Value 
                    // Should contain branching for DBNull.Value when property == null
                    var castPropertyToObject = Expression.Convert(property, typeof(object));


                    // The sql parameter
                    var sqlParm = new SqlParameter(reflectionProperty.Name, null);

                    // input parameter for assignment action
                    var sqlValueProp = Expression.Property(sqlParmAccessor, "Value");

                    // Expression assigning the retrieved property from input object 
                    // to the sql parameters 'Value' property
                    var dbnull = Expression.Constant(DBNull.Value);
                    var coalesce = Expression.Coalesce(castPropertyToObject, dbnull);
                    var assign = Expression.Assign(sqlValueProp, coalesce);

                    // Compile into action (removes reflection and makes real CLR object)
                    var assigner = Expression.Lambda<Action<T, SqlParameter>>(assign, accessor, sqlParmAccessor).Compile();

                    yield return
                        new Mapping<T>(reflectionProperty.Name, // Table name
                            sqlParm, // The constructed sql parameter
                            assigner); // The action assigning from the input <T> 

                }
            }
        }

        public static void Main(string[] args)
        {
            var sqlStuff = (new Mapper<Data>().GetMappingElements()).ToList();

            var sqlFieldsList = string.Join(", ", sqlStuff.Select(x => x.FieldName));
            var sqlValuesList = string.Join(", ", sqlStuff.Select(x => '@' + x.SqlParameter.ParameterName));

            var sqlStmt = string.Format("INSERT INTO test ({0}) VALUES ({1})", sqlFieldsList, sqlValuesList);

            var dataObjects = Enumerable.Range(1, 100).Select(id => new Data { Foo = 1.0 / id, ID = id, Title = null });

            var sw = Stopwatch.StartNew();

            using (SqlConnection cnn = new SqlConnection(@"server=.\sqlexpress;database=test;integrated security=SSPI"))
            {
                cnn.Open();

                SqlCommand cmd = new SqlCommand(sqlStmt, cnn);
                cmd.Parameters.AddRange(sqlStuff.Select(x => x.SqlParameter).ToArray());

                dataObjects.ToList()
                    .ForEach(dto =>
                        {
                            sqlStuff.ForEach(x => x.SqlParameterAssignment(dto, x.SqlParameter));
                            cmd.ExecuteNonQuery();
                        });
            }


            Console.WriteLine("Done in: " + sw.Elapsed);
        }
    }

    public class Data
    {
        public string Title { get; set; }
        public int ID { get; set; }
        public double Foo { get; set; }
    }
}