executereader - sqldatareader to dataset c#

Obtenga un IDataReader de una lista escrita

Question

Tengo una List<MyObject> con un millón de elementos. (En realidad es una Colección SubSonic pero no se carga desde la base de datos).

Actualmente estoy usando SqlBulkCopy de la siguiente manera:

private string FastInsertCollection(string tableName, DataTable tableData)
{
    string sqlConn = ConfigurationManager.ConnectionStrings[SubSonicConfig.DefaultDataProvider.ConnectionStringName].ConnectionString;
    using (SqlBulkCopy s = new SqlBulkCopy(sqlConn, SqlBulkCopyOptions.TableLock))
    {
        s.DestinationTableName = tableName;
        s.BatchSize = 5000;
        s.WriteToServer(tableData);
        s.BulkCopyTimeout = SprocTimeout;
        s.Close();
    }
    return sqlConn;
}

Utilizo MyObjectCollection.ToDataTable () de SubSonic para construir el DataTable de mi colección. Sin embargo, esto duplica los objetos en la memoria y es ineficiente. Me gustaría usar el método SqlBulkCopy.WriteToServer que usa un IDataReader en lugar de un DataTable para no duplicar mi colección en la memoria.

¿Cuál es la forma más fácil de obtener un IDataReader de mi lista? Supongo que podría implementar un lector de datos personalizado (como aquí http://blogs.microsoft.co.il/blogs/aviwortzel/archive/2008/05/06/implementing-sqlbulkcopy-in-linq-to-sql.aspx ) , pero debe haber algo más simple que pueda hacer sin escribir un montón de código genérico.

Editar: no parece que uno pueda generar fácilmente un IDataReader a partir de una colección de objetos. Aceptando la respuesta actual a pesar de que esperaba algo incorporado en el marco.

Answer 1

Gracias a Sky Sanders por su respuesta inicial, fue de gran ayuda.

Escribí una versión genérica del EnumerableDataReader de Sky Sanders pero hice los siguientes cambios:

• El lector ahora admite propiedades públicas y campos públicos.
• El constructor ahora toma una lista de nombres de campo / propiedad que deberían estar disponibles en el DataReader. Esto permite limitar y definir el orden de las propiedades y / o campos para que coincidan con el diseño de su tabla. Si no se proporciona una lista de campos, solo hay un campo disponible, es decir, el objeto en sí, de esta manera el lector puede usarse con, por ejemplo, una Lista.
• El código original que utiliza DynamicMethod e ILGenerator no funcionaba con las interfaces y requería un cambio de código para las estructuras, por lo que lo cambié usando Linq.Expressions que parece funcionar en todos los casos (y como un bono es más compacto). El rendimiento de los campos es el mismo que el de ILGenerator, el rendimiento de las propiedades parece marginalmente más lento que con el ILGenerator, pero aún más rápido que el reflejo.
• Quizás este no sea un punto positivo, pero puse todo el código en una clase (con algunas subclases de ayuda), eliminando todo el código innecesario. (No estoy diciendo que el código no fuera útil, simplemente no lo necesitaba en mi caso).

Espero que esto ayude y si tiene comentarios, correcciones o mejoras, dígalo :)

/// <summary>
/// IDataReader that can be used for "reading" an IEnumerable<T> collection
/// </summary>
public class EnumerableDataReader<T> : IDataReader
{
    /// <summary>
    /// Constructor
    /// </summary>
    /// <param name="collection">The collection to be read</param>
    /// <param name="fields">The list of public field/properties to read from each T (in order), OR if no fields are given only one field will be available: T itself</param>
    public EnumerableDataReader(IEnumerable<T> collection, params string[] fields)
    {
        if (collection == null)
            throw new ArgumentNullException("collection");

        m_Enumerator = collection.GetEnumerator();

        if (m_Enumerator == null)
            throw new NullReferenceException("collection does not implement GetEnumerator");

        SetFields(fields);
    }
    private IEnumerator<T> m_Enumerator;
    private T m_Current = default(T);
    private bool m_EnumeratorState = false;

    private void SetFields(ICollection<string> fields)
    {
        if (fields.Count > 0)
        {
            Type type = typeof(T);
            foreach (string field in fields)
            {
                PropertyInfo pInfo = type.GetProperty(field);
                if (pInfo != null)
                    m_Fields.Add(new Property(pInfo));
                else
                {
                    FieldInfo fInfo = type.GetField(field);
                    if (fInfo != null)
                        m_Fields.Add(new Field(fInfo));
                    else
                        throw new NullReferenceException(string.Format("EnumerableDataReader<T>: Missing property or field ''{0}'' in Type ''{1}''.", field, type.Name));
                }
            }
        }
        else
            m_Fields.Add(new Self());
    }
    private List<BaseField> m_Fields = new List<BaseField>();

    #region IDisposable Members
    public void Dispose()
    {
        if (m_Enumerator != null)
        {
            m_Enumerator.Dispose();
            m_Enumerator = null;
            m_Current = default(T);
            m_EnumeratorState = false;
        }
        m_Closed = true;
    }
    #endregion

    #region IDataReader Members
    public void Close()
    {
        m_Closed = true;
    }
    private bool m_Closed = false;

    public int Depth
    {
        get { return 0; }
    }

    public DataTable GetSchemaTable()
    {
        var dt = new DataTable();
        foreach (BaseField field in m_Fields)
        {
            dt.Columns.Add(new DataColumn(field.Name, field.Type));
        }
        return dt;
    }

    public bool IsClosed
    {
        get { return m_Closed; }
    }

    public bool NextResult()
    {
        return false;
    }

    public bool Read()
    {
        if (IsClosed)
            throw new InvalidOperationException("DataReader is closed");
        m_EnumeratorState = m_Enumerator.MoveNext();
        m_Current = m_EnumeratorState ? m_Enumerator.Current : default(T);
        return m_EnumeratorState;
    }

    public int RecordsAffected
    {
        get { return -1; }
    }
    #endregion

    #region IDataRecord Members
    public int FieldCount
    {
        get { return m_Fields.Count; }
    }

    public Type GetFieldType(int i)
    {
        if (i < 0 || i >= m_Fields.Count)
            throw new IndexOutOfRangeException();
        return m_Fields[i].Type;
    }

    public string GetDataTypeName(int i)
    {
        return GetFieldType(i).Name;
    }

    public string GetName(int i)
    {
        if (i < 0 || i >= m_Fields.Count)
            throw new IndexOutOfRangeException();
        return m_Fields[i].Name;
    }

    public int GetOrdinal(string name)
    {
        for (int i = 0; i < m_Fields.Count; i++)
            if (m_Fields[i].Name == name)
                return i;
        throw new IndexOutOfRangeException("name");
    }

    public bool IsDBNull(int i)
    {
        return GetValue(i) == null;
    }

    public object this[string name]
    {
        get { return GetValue(GetOrdinal(name)); }
    }

    public object this[int i]
    {
        get { return GetValue(i); }
    }

    public object GetValue(int i)
    {
        if (IsClosed || !m_EnumeratorState)
            throw new InvalidOperationException("DataReader is closed or has reached the end of the enumerator");
        if (i < 0 || i >= m_Fields.Count)
            throw new IndexOutOfRangeException();
        return m_Fields[i].GetValue(m_Current);
    }

    public int GetValues(object[] values)
    {
        int length = Math.Min(m_Fields.Count, values.Length);
        for (int i = 0; i < length; i++)
            values[i] = GetValue(i);
        return length;
    }

    public bool GetBoolean(int i) { return (bool)GetValue(i); }
    public byte GetByte(int i) { return (byte)GetValue(i); }
    public char GetChar(int i) { return (char)GetValue(i); }
    public DateTime GetDateTime(int i) { return (DateTime)GetValue(i); }
    public decimal GetDecimal(int i) { return (decimal)GetValue(i); }
    public double GetDouble(int i) { return (double)GetValue(i); }
    public float GetFloat(int i) { return (float)GetValue(i); }
    public Guid GetGuid(int i) {return (Guid)GetValue(i); }
    public short GetInt16(int i) { return (short)GetValue(i); }
    public int GetInt32(int i) { return (int)GetValue(i); }
    public long GetInt64(int i) { return (long)GetValue(i); }
    public string GetString(int i) { return (string)GetValue(i); }

    public long GetBytes(int i, long fieldOffset, byte[] buffer, int bufferoffset, int length) { throw new NotSupportedException(); }
    public long GetChars(int i, long fieldoffset, char[] buffer, int bufferoffset, int length) { throw new NotSupportedException(); }
    public IDataReader GetData(int i) { throw new NotSupportedException(); }
    #endregion

    #region Helper Classes
    private abstract class BaseField
    {
        public abstract Type Type { get; }
        public abstract string Name { get; }
        public abstract object GetValue(T instance);

        protected static void AddGetter(Type classType, string fieldName, Func<T, object> getter)
        {
            m_GetterDictionary.Add(string.Concat(classType.FullName, fieldName), getter);
        }

        protected static Func<T, object> GetGetter(Type classType, string fieldName)
        {
            Func<T, object> getter = null;
            if (m_GetterDictionary.TryGetValue(string.Concat(classType.FullName, fieldName), out getter))
                return getter;
            return null;
        }
        private static Dictionary<string, Func<T, object>> m_GetterDictionary = new Dictionary<string, Func<T, object>>();
    }

    private class Property : BaseField
    {
        public Property(PropertyInfo info)
        {
            m_Info = info;
            m_DynamicGetter = CreateGetMethod(info);
        }
        private PropertyInfo m_Info;
        private Func<T, object> m_DynamicGetter;

        public override Type Type { get { return m_Info.PropertyType; } }
        public override string Name { get { return m_Info.Name; } }

        public override object GetValue(T instance)
        {
            //return m_Info.GetValue(instance, null); // Reflection is slow
            return m_DynamicGetter(instance);
        }

        // Create dynamic method for faster access instead via reflection
        private Func<T, object> CreateGetMethod(PropertyInfo propertyInfo)
        {
            Type classType = typeof(T);
            Func<T, object> dynamicGetter = GetGetter(classType, propertyInfo.Name);
            if (dynamicGetter == null)
            {
                ParameterExpression instance = Expression.Parameter(classType);
                MemberExpression property = Expression.Property(instance, propertyInfo);
                UnaryExpression convert = Expression.Convert(property, typeof(object));
                dynamicGetter = (Func<T, object>)Expression.Lambda(convert, instance).Compile();
                AddGetter(classType, propertyInfo.Name, dynamicGetter);
            }

            return dynamicGetter;
        }
    }

    private class Field : BaseField
    {
        public Field(FieldInfo info)
        {
            m_Info = info;
            m_DynamicGetter = CreateGetMethod(info);
        }
        private FieldInfo m_Info;
        private Func<T, object> m_DynamicGetter;

        public override Type Type { get { return m_Info.FieldType; } }
        public override string Name { get { return m_Info.Name; } }

        public override object GetValue(T instance)
        {
            //return m_Info.GetValue(instance); // Reflection is slow
            return m_DynamicGetter(instance);
        }

        // Create dynamic method for faster access instead via reflection
        private Func<T, object> CreateGetMethod(FieldInfo fieldInfo)
        {
            Type classType = typeof(T);
            Func<T, object> dynamicGetter = GetGetter(classType, fieldInfo.Name);
            if (dynamicGetter == null)
            {
                ParameterExpression instance = Expression.Parameter(classType);
                MemberExpression property = Expression.Field(instance, fieldInfo);
                UnaryExpression convert = Expression.Convert(property, typeof(object));
                dynamicGetter = (Func<T, object>)Expression.Lambda(convert, instance).Compile();
                AddGetter(classType, fieldInfo.Name, dynamicGetter);
            }

            return dynamicGetter;
        }
    }

    private class Self : BaseField
    {
        public Self()
        {
            m_Type = typeof(T);
        }
        private Type m_Type;

        public override Type Type { get { return m_Type; } }
        public override string Name { get { return string.Empty; } }
        public override object GetValue(T instance) { return instance; }
    }
    #endregion
}

Answer 2

Obtenga la última versión del código en esta publicación

Nada como el cambio de código a la vista: aquí hay una implementación bastante completa. Puede instanciar un IDataReader sobre IList IEnumerable, IEnumerable (ergo IQueryable). No existe un motivo convincente para exponer un parámetro de tipo genérico en el lector y, al omitirlo, puedo permitir IEnumerable <''a> (tipos anónimos). Ver pruebas

La fuente, menos xmldocs, es lo suficientemente corta como para incluirla aquí con un par de pruebas. El resto de la fuente, con xmldocs, y pruebas está here en Salient.Data.

using System;
using System.Linq;
using NUnit.Framework;

namespace Salient.Data.Tests
{
    [TestFixture]
    public class EnumerableDataReaderEFFixture
    {
        [Test]
        public void TestEnumerableDataReaderWithIQueryableOfAnonymousType()
        {
            var ctx = new NorthwindEntities();

            var q =
                ctx.Orders.Where(o => o.Customers.CustomerID == "VINET").Select(
                    o =>
                    new
                        {
                            o.OrderID,
                            o.OrderDate,
                            o.Customers.CustomerID,
                            Total =
                        o.Order_Details.Sum(
                        od => od.Quantity*((float) od.UnitPrice - ((float) od.UnitPrice*od.Discount)))
                        });

            var r = new EnumerableDataReader(q);
            while (r.Read())
            {
                var values = new object[4];
                r.GetValues(values);
                Console.WriteLine("{0} {1} {2} {3}", values);
            }
        }
    }
}

using System;
using System.Collections;
using System.Collections.Generic;
using System.Data;
using NUnit.Framework;

namespace Salient.Data.Tests
{
    public class DataObj
    {
        public string Name { get; set; }
        public int Age { get; set; }
    }

    [TestFixture]
    public class EnumerableDataReaderFixture
    {

        private static IEnumerable<DataObj> DataSource
        {
            get
            {
                return new List<DataObj>
                           {
                               new DataObj {Name = "1", Age = 16},
                               new DataObj {Name = "2", Age = 26},
                               new DataObj {Name = "3", Age = 36},
                               new DataObj {Name = "4", Age = 46}
                           };
            }
        }

        [Test]
        public void TestIEnumerableCtor()
        {
            var r = new EnumerableDataReader(DataSource, typeof(DataObj));
            while (r.Read())
            {
                var values = new object[2];
                int count = r.GetValues(values);
                Assert.AreEqual(2, count);

                values = new object[1];
                count = r.GetValues(values);
                Assert.AreEqual(1, count);

                values = new object[3];
                count = r.GetValues(values);
                Assert.AreEqual(2, count);

                Assert.IsInstanceOf(typeof(string), r.GetValue(0));
                Assert.IsInstanceOf(typeof(int), r.GetValue(1));

                Console.WriteLine("Name: {0}, Age: {1}", r.GetValue(0), r.GetValue(1));
            }
        }

        [Test]
        public void TestIEnumerableOfAnonymousType()
        {
            // create generic list
            Func<Type, IList> toGenericList =
                type => (IList)Activator.CreateInstance(typeof(List<>).MakeGenericType(new[] { type }));

            // create generic list of anonymous type
            IList listOfAnonymousType = toGenericList(new { Name = "1", Age = 16 }.GetType());

            listOfAnonymousType.Add(new { Name = "1", Age = 16 });
            listOfAnonymousType.Add(new { Name = "2", Age = 26 });
            listOfAnonymousType.Add(new { Name = "3", Age = 36 });
            listOfAnonymousType.Add(new { Name = "4", Age = 46 });

            var r = new EnumerableDataReader(listOfAnonymousType);
            while (r.Read())
            {
                var values = new object[2];
                int count = r.GetValues(values);
                Assert.AreEqual(2, count);

                values = new object[1];
                count = r.GetValues(values);
                Assert.AreEqual(1, count);

                values = new object[3];
                count = r.GetValues(values);
                Assert.AreEqual(2, count);

                Assert.IsInstanceOf(typeof(string), r.GetValue(0));
                Assert.IsInstanceOf(typeof(int), r.GetValue(1));

                Console.WriteLine("Name: {0}, Age: {1}", r.GetValue(0), r.GetValue(1));
            }
        }

        [Test]
        public void TestIEnumerableOfTCtor()
        {
            var r = new EnumerableDataReader(DataSource);
            while (r.Read())
            {
                var values = new object[2];
                int count = r.GetValues(values);
                Assert.AreEqual(2, count);

                values = new object[1];
                count = r.GetValues(values);
                Assert.AreEqual(1, count);

                values = new object[3];
                count = r.GetValues(values);
                Assert.AreEqual(2, count);

                Assert.IsInstanceOf(typeof(string), r.GetValue(0));
                Assert.IsInstanceOf(typeof(int), r.GetValue(1));

                Console.WriteLine("Name: {0}, Age: {1}", r.GetValue(0), r.GetValue(1));
            }
        } 
        // remaining tests omitted for brevity
    }
}

/*!
 * Project: Salient.Data
 * File   : EnumerableDataReader.cs
 * http://spikes.codeplex.com
 *
 * Copyright 2010, Sky Sanders
 * Dual licensed under the MIT or GPL Version 2 licenses.
 * See LICENSE.TXT
 * Date: Sat Mar 28 2010 
 */


using System;
using System.Collections;
using System.Collections.Generic;

namespace Salient.Data
{
    /// <summary>
    /// Creates an IDataReader over an instance of IEnumerable&lt;> or IEnumerable.
    /// Anonymous type arguments are acceptable.
    /// </summary>
    public class EnumerableDataReader : ObjectDataReader
    {
        private readonly IEnumerator _enumerator;
        private readonly Type _type;
        private object _current;

        /// <summary>
        /// Create an IDataReader over an instance of IEnumerable&lt;>.
        /// 
        /// Note: anonymous type arguments are acceptable.
        /// 
        /// Use other constructor for IEnumerable.
        /// </summary>
        /// <param name="collection">IEnumerable&lt;>. For IEnumerable use other constructor and specify type.</param>
        public EnumerableDataReader(IEnumerable collection)
        {
            // THANKS DANIEL!
            foreach (Type intface in collection.GetType().GetInterfaces())
            {
                if (intface.IsGenericType && intface.GetGenericTypeDefinition() == typeof (IEnumerable<>))
                {
                    _type = intface.GetGenericArguments()[0]; 
                }
            }

            if (_type ==null && collection.GetType().IsGenericType)
            {
                _type = collection.GetType().GetGenericArguments()[0];

            }


            if (_type == null )
            {
                throw new ArgumentException(
                    "collection must be IEnumerable<>. Use other constructor for IEnumerable and specify type");
            }

            SetFields(_type);

            _enumerator = collection.GetEnumerator();

        }

        /// <summary>
        /// Create an IDataReader over an instance of IEnumerable.
        /// Use other constructor for IEnumerable&lt;>
        /// </summary>
        /// <param name="collection"></param>
        /// <param name="elementType"></param>
        public EnumerableDataReader(IEnumerable collection, Type elementType)
            : base(elementType)
        {
            _type = elementType;
            _enumerator = collection.GetEnumerator();
        }

        /// <summary>
        /// Helper method to create generic lists from anonymous type
        /// </summary>
        /// <param name="type"></param>
        /// <returns></returns>
        public static IList ToGenericList(Type type)
        {
            return (IList) Activator.CreateInstance(typeof (List<>).MakeGenericType(new[] {type}));
        }

        /// <summary>
        /// Return the value of the specified field.
        /// </summary>
        /// <returns>
        /// The <see cref="T:System.Object"/> which will contain the field value upon return.
        /// </returns>
        /// <param name="i">The index of the field to find. 
        /// </param><exception cref="T:System.IndexOutOfRangeException">The index passed was outside the range of 0 through <see cref="P:System.Data.IDataRecord.FieldCount"/>. 
        /// </exception><filterpriority>2</filterpriority>
        public override object GetValue(int i)
        {
            if (i < 0 || i >= Fields.Count)
            {
                throw new IndexOutOfRangeException();
            }

            return Fields[i].Getter(_current);
        }

        /// <summary>
        /// Advances the <see cref="T:System.Data.IDataReader"/> to the next record.
        /// </summary>
        /// <returns>
        /// true if there are more rows; otherwise, false.
        /// </returns>
        /// <filterpriority>2</filterpriority>
        public override bool Read()
        {
            bool returnValue = _enumerator.MoveNext();
            _current = returnValue ? _enumerator.Current : _type.IsValueType ? Activator.CreateInstance(_type) : null;
            return returnValue;
        }
    }
}

// <copyright project="Salient.Data" file="ObjectDataReader.cs" company="Sky Sanders">
// This source is a Public Domain Dedication.
// Please see http://spikes.codeplex.com/ for details.   
// Attribution is appreciated
// </copyright> 
// <version>1.0</version>


using System;
using System.Collections.Generic;
using System.Data;
using Salient.Reflection;

namespace Salient.Data
{
    public abstract class ObjectDataReader : IDataReader
    {
        protected bool Closed;
        protected IList<DynamicProperties.Property> Fields;

        protected ObjectDataReader()
        {
        }

        protected ObjectDataReader(Type elementType)
        {
            SetFields(elementType);
            Closed = false;
        }

        #region IDataReader Members

        public abstract object GetValue(int i);
        public abstract bool Read();

        #endregion

        #region Implementation of IDataRecord

        public int FieldCount
        {
            get { return Fields.Count; }
        }

        public virtual int GetOrdinal(string name)
        {
            for (int i = 0; i < Fields.Count; i++)
            {
                if (Fields[i].Info.Name == name)
                {
                    return i;
                }
            }

            throw new IndexOutOfRangeException("name");
        }

        object IDataRecord.this[int i]
        {
            get { return GetValue(i); }
        }

        public virtual bool GetBoolean(int i)
        {
            return (Boolean) GetValue(i);
        }

       public virtual byte GetByte(int i)
        {
            return (Byte) GetValue(i);
        }

        public virtual char GetChar(int i)
        {
            return (Char) GetValue(i);
        }

        public virtual DateTime GetDateTime(int i)
        {
            return (DateTime) GetValue(i);
        }

        public virtual decimal GetDecimal(int i)
        {
            return (Decimal) GetValue(i);
        }

        public virtual double GetDouble(int i)
        {
            return (Double) GetValue(i);
        }

        public virtual Type GetFieldType(int i)
        {
            return Fields[i].Info.PropertyType;
        }

        public virtual float GetFloat(int i)
        {
            return (float) GetValue(i);
        }

        public virtual Guid GetGuid(int i)
        {
            return (Guid) GetValue(i);
        }

        public virtual short GetInt16(int i)
        {
            return (Int16) GetValue(i);
        }

        public virtual int GetInt32(int i)
        {
            return (Int32) GetValue(i);
        }

        public virtual long GetInt64(int i)
        {
            return (Int64) GetValue(i);
        }

        public virtual string GetString(int i)
        {
            return (string) GetValue(i);
        }

        public virtual bool IsDBNull(int i)
        {
            return GetValue(i) == null;
        }

        object IDataRecord.this[string name]
        {
            get { return GetValue(GetOrdinal(name)); }
        }


        public virtual string GetDataTypeName(int i)
        {
            return GetFieldType(i).Name;
        }


        public virtual string GetName(int i)
        {
            if (i < 0 || i >= Fields.Count)
            {
                throw new IndexOutOfRangeException("name");
            }
            return Fields[i].Info.Name;
        }

        public virtual int GetValues(object[] values)
        {
            int i = 0;
            for (; i < Fields.Count; i++)
            {
                if (values.Length <= i)
                {
                    return i;
                }
                values[i] = GetValue(i);
            }
            return i;
        }

        public virtual IDataReader GetData(int i)
        {
            // need to think about this one
            throw new NotImplementedException();
        }

        public virtual long GetBytes(int i, long fieldOffset, byte[] buffer, int bufferoffset, int length)
        {
            // need to keep track of the bytes got for each record - more work than i want to do right now
            // http://msdn.microsoft.com/en-us/library/system.data.idatarecord.getbytes.aspx
            throw new NotImplementedException();
        }

        public virtual long GetChars(int i, long fieldoffset, char[] buffer, int bufferoffset, int length)
        {
            // need to keep track of the bytes got for each record - more work than i want to do right now
            // http://msdn.microsoft.com/en-us/library/system.data.idatarecord.getchars.aspx
            throw new NotImplementedException();
        }

        #endregion

        #region Implementation of IDataReader

        public virtual void Close()
        {
            Closed = true;
        }


        public virtual DataTable GetSchemaTable()
        {
            var dt = new DataTable();
            foreach (DynamicProperties.Property field in Fields)
            {
                dt.Columns.Add(new DataColumn(field.Info.Name, field.Info.PropertyType));
            }
            return dt;
        }

        public virtual bool NextResult()
        {
            throw new NotImplementedException();
        }


        public virtual int Depth
        {
            get { throw new NotImplementedException(); }
        }

        public virtual bool IsClosed
        {
            get { return Closed; }
        }

        public virtual int RecordsAffected
        {
            get
            {
                // assuming select only?
                return -1;
            }
        }

        #endregion

        #region Implementation of IDisposable

        public virtual void Dispose()
        {
            Fields = null;
        }

        #endregion

        protected void SetFields(Type elementType)
        {
            Fields = DynamicProperties.CreatePropertyMethods(elementType);
        }
    }
}

// <copyright project="Salient.Reflection" file="DynamicProperties.cs" company="Sky Sanders">
// This source is a Public Domain Dedication.
// Please see http://spikes.codeplex.com/ for details.   
// Attribution is appreciated
// </copyright> 
// <version>1.0</version>
using System;
using System.Collections.Generic;
using System.Reflection;
using System.Reflection.Emit;

namespace Salient.Reflection
{
    /// <summary>
    /// Gets IL setters and getters for a property.
    /// 
    /// started with http://jachman.wordpress.com/2006/08/22/2000-faster-using-dynamic-method-calls/
    /// </summary>
    public static class DynamicProperties
    {
        #region Delegates

        public delegate object GenericGetter(object target);

        public delegate void GenericSetter(object target, object value);

        #endregion

        public static IList<Property> CreatePropertyMethods(Type T)
        {
            var returnValue = new List<Property>();

            foreach (PropertyInfo prop in T.GetProperties())
            {
                returnValue.Add(new Property(prop));
            }
            return returnValue;
        }


        public static IList<Property> CreatePropertyMethods<T>()
        {
            var returnValue = new List<Property>();

            foreach (PropertyInfo prop in typeof (T).GetProperties())
            {
                returnValue.Add(new Property(prop));
            }
            return returnValue;
        }


        /// <summary>
        /// Creates a dynamic setter for the property
        /// </summary>
        /// <param name="propertyInfo"></param>
        /// <returns></returns>
        public static GenericSetter CreateSetMethod(PropertyInfo propertyInfo)
        {
            /*
            * If there''s no setter return null
            */
            MethodInfo setMethod = propertyInfo.GetSetMethod();
            if (setMethod == null)
                return null;

            /*
            * Create the dynamic method
            */
            var arguments = new Type[2];
            arguments[0] = arguments[1] = typeof (object);

            var setter = new DynamicMethod(
                String.Concat("_Set", propertyInfo.Name, "_"),
                typeof (void), arguments, propertyInfo.DeclaringType);
            ILGenerator generator = setter.GetILGenerator();
            generator.Emit(OpCodes.Ldarg_0);
            generator.Emit(OpCodes.Castclass, propertyInfo.DeclaringType);
            generator.Emit(OpCodes.Ldarg_1);

            if (propertyInfo.PropertyType.IsClass)
                generator.Emit(OpCodes.Castclass, propertyInfo.PropertyType);
            else
                generator.Emit(OpCodes.Unbox_Any, propertyInfo.PropertyType);

            generator.EmitCall(OpCodes.Callvirt, setMethod, null);
            generator.Emit(OpCodes.Ret);

            /*
            * Create the delegate and return it
            */
            return (GenericSetter) setter.CreateDelegate(typeof (GenericSetter));
        }


        /// <summary>
        /// Creates a dynamic getter for the property
        /// </summary>
        /// <param name="propertyInfo"></param>
        /// <returns></returns>
        public static GenericGetter CreateGetMethod(PropertyInfo propertyInfo)
        {
            /*
            * If there''s no getter return null
            */
            MethodInfo getMethod = propertyInfo.GetGetMethod();
            if (getMethod == null)
                return null;

            /*
            * Create the dynamic method
            */
            var arguments = new Type[1];
            arguments[0] = typeof (object);

            var getter = new DynamicMethod(
                String.Concat("_Get", propertyInfo.Name, "_"),
                typeof (object), arguments, propertyInfo.DeclaringType);
            ILGenerator generator = getter.GetILGenerator();
            generator.DeclareLocal(typeof (object));
            generator.Emit(OpCodes.Ldarg_0);
            generator.Emit(OpCodes.Castclass, propertyInfo.DeclaringType);
            generator.EmitCall(OpCodes.Callvirt, getMethod, null);

            if (!propertyInfo.PropertyType.IsClass)
                generator.Emit(OpCodes.Box, propertyInfo.PropertyType);

            generator.Emit(OpCodes.Ret);

            /*
            * Create the delegate and return it
            */
            return (GenericGetter) getter.CreateDelegate(typeof (GenericGetter));
        }

        #region Nested type: Property

        public class Property
        {
            public GenericGetter Getter;
            public PropertyInfo Info;
            public GenericSetter Setter;

            public Property(PropertyInfo info)
            {
                Info = info;
                Setter = CreateSetMethod(info);
                Getter = CreateGetMethod(info);
            }
        }

        #endregion

        ///// <summary>
        ///// An expression based Getter getter found in comments. untested.
        ///// Q: i don''t see a reciprocal setter expression?
        ///// </summary>
        ///// <typeparam name="T"></typeparam>
        ///// <param name="propName"></param>
        ///// <returns></returns>
        //public static Func<T> CreateGetPropValue<T>(string propName)
        //{
        //    var param = Expression.Parameter(typeof(object), "container");
        //    var func = Expression.Lambda(
        //    Expression.Convert(Expression.PropertyOrField(Expression.Convert(param, typeof(T)), propName), typeof(object)), param);
        //    return (Func<T>)func.Compile();
        //}
    }
}

Answer 3

Puedes usar el FastMember Marc Gravell:

IDataReader reader = ObjectReader.Create(myEnumerable); //all columns
IDataReader reader = ObjectReader.Create(myEnumerable, "Id", "Name", "Description");

Además de abstraer la lógica de creación, también usa IL para obtener los valores de propiedad / campo, que es más rápido que la reflexión.