如何将DataReader映射到类属性并保持性能？

Question

前言:

1. 使用DbProviderFactories创建所有数据连接字符串,连接等.
2. 代码是来自多个库的C#和VB.Net混合.

我正在将DbDataReader映射到实体并具有一些基准:

[0] retrieved 159180 records in 45135 ms
[1] retrieved 159180 records in 45008 ms
[2] retrieved 159180 records in 44814 ms
[3] retrieved 159180 records in 44987 ms
[4] retrieved 159180 records in 44914 ms
[5] retrieved 159180 records in 45224 ms
[6] retrieved 159180 records in 45829 ms
[7] retrieved 159180 records in 60762 ms
[8] retrieved 159180 records in 52128 ms
[9] retrieved 159180 records in 47982 ms  

考虑到从Sql Server Management Studio查询只需要17秒,这是一个非常大的时间和极差.我的选择声明:

"SELECT*FROM tbl_MyTable"

表包含43个字段,可能未按其应有的最佳索引; 但是,执行全选,我不希望索引有问题.所以......这就是我在做的事情:

定义一个实体:

public class Concept
{
    #region Columns
    [DataParameter("ConceptID", DbType.Int32)]
    public Int32 ConceptID
    { get; set; }
    [DataParameter("ConceptName", DbType.String)]
    public string ConceptName
    { get; set; }
    [DataParameter("ConceptTypeID", DbType.Int32)]
    public Int32 ConceptTypeID
    { get; set; }
    [DataParameter("ActiveYN", DbType.Boolean)]
    public bool ActiveYN
    { get; set; }
    #endregion
}

查询DataReader:

for (int i = 0; i <= 99; i++)
{
    sw.Start();
    var results = session.QueryReader<Concept>(
        new SqlCommand(command), dr => new Concept());

    sw.Stop();

    Console.WriteLine("[{0}] retrieved {1} records in {2} ms", i, results.Count(), sw.ElapsedMilliseconds);
    sw.Reset();
}

......打电话:

Public Function QueryReader(Of TEntity As {Class, New})(ByVal Command As DbCommand, _
                                                        ByVal Projection As Func(Of DbDataReader, TEntity)) _
                                                        As IEnumerable(Of TEntity)

    Dim list As IEnumerable(Of TEntity)

    Command.Connection = dataReader.NewConnection
    Command.Connection.Open()

    Using _reader As DbDataReader = Command.ExecuteReader()
        list = _reader.Query(Of TEntity)(Projection).ToList()
    End Using

    Command.Connection.Close()

    Return list
End Function

...和扩展方法QueryReader<T>:编辑新TEntity()的位置 - 谢谢@Henk

public static IEnumerable<TEntity> Query<TEntity>(this DbDataReader Reader,
    Func<DbDataReader, TEntity> Projection)
    where TEntity : class, new()
{
    //   moving this reflection to another class
    Dictionary<string, PropertyInfo> props;

    while (Reader.Read())
    {
        TEntity entity = new TEntity();

        if (!entities.TryGetValue(typeof(TEntity).ToString(), out props))
        {
            //  reflection over TEntity
            props = (from p in entity.GetType().GetProperties()
                     from a in p.GetCustomAttributes(typeof(DataParameterAttribute), false)
                     select p)
                     .ToDictionary(p => p.Name);

            entities.Add(typeof(TEntity).ToString(), props);
        }

        foreach (KeyValuePair<string, PropertyInfo> field in props)
        {
            if (null != Reader[field.Key] && Reader[field.Key] != DBNull.Value)
            { field.Value.SetValue(entity, Reader[field.Key], null); }
        }

        yield return entity;
    }
}

任何有关提高性能的建议都将受到高度赞赏......

---

更新

我实现了@EtienneT建议的dapper-dot-net - 这里是检索时间:

[0] retrieved 159180 records in 6874 ms
[1] retrieved 159180 records in 6866 ms
[2] retrieved 159180 records in 6570 ms
[3] retrieved 159180 records in 6785 ms
[4] retrieved 159180 records in 6693 ms
[5] retrieved 159180 records in 6735 ms
[6] retrieved 159180 records in 6627 ms
[7] retrieved 159180 records in 6739 ms
[8] retrieved 159180 records in 6569 ms
[9] retrieved 159180 records in 6666 ms

Answer 1

您是否考虑过像dapper.net这样的微型ORM？

https://github.com/StackExchange/dapper-dot-net

它由StackOverflow的开发人员创建,并将SQL查询直接映射到您的对象.它生成并缓存IL代码以将SQL结果映射到对象.因此每个类型只生成一次IL代码.从未使用过这个,但如果您需要将SQL结果映射到.net对象的性能,那么它就是您需要的库.