Dapper是一個(gè)輕型的ORM類。代碼就一個(gè)SqlMapper.cs文件,主要是IDbConnection的擴(kuò)展方法，編譯后就40K的一個(gè)很小的dll。官方站點(diǎn)http://code.google.com/p/dapper-dot-net/ ，也可以通過Nuget進(jìn)行安裝

• Dapper很快。Dapper的速度接近與IDataReader。
• Dapper支持主流數(shù)據(jù)庫(kù) Mysql,SqlLite,Mssql2000,Mssql2005,Oracle等一系列的數(shù)據(jù)庫(kù)
• 支持多表并聯(lián)的對(duì)象。支持一對(duì)多 多對(duì)多的關(guān)系，并且沒侵入性。
• 原理通過Emit反射IDataReader的序列隊(duì)列，來快速的得到和產(chǎn)生對(duì)象
• Dapper語法十分簡(jiǎn)單。并且無須遷就數(shù)據(jù)庫(kù)的設(shè)計(jì)

Query()方法：
Query()是IDbConnection擴(kuò)展方法并且重載了,從數(shù)據(jù)庫(kù)里提取信息，并用來填充我們的業(yè)務(wù)對(duì)象模型。

                var counters = new List<Tuple<int, PerformanceCounter>>();
                using (var conn = new SqlConnection(ConfigurationManager.ConnectionStrings["SqlDiagnosticsDb"].ConnectionString))
                {
                    conn.Open();
                    string sql = string.Format("select Id,ServiceName,CategoryName,CounterName,InstanceName from service_counters where MachineName='{0}'",machineName);
                    foreach (var counter in conn.Query<ServiceCounter>(sql))
                    {
                        logger.InfoFormat(@"Creating performance counter: {0}\{1}\{2}\{3}", counter.MachineName ?? ".", counter.CategoryName,
                                            counter.CounterName, counter.InstanceName);
                        var perfCounter = new PerformanceCounter(counter.CategoryName, counter.CounterName, counter.InstanceName, counter.MachineName ?? ".");
                        counters.Add(new Tuple<int, PerformanceCounter>(counter.Id, perfCounter));
                        // first value doesn't matter so we should call the counter at least once
                        try { perfCounter.NextValue(); }
                        catch { }
                    }
                }

下面是ServiceCounter的定義

public class ServiceCounter
{
    public int Id { get; set; }

    public String ServiceName { get; set; }

    public String MachineName { get; set; }
    public String CategoryName { get; set; }
    public String CounterName { get; set; }
    public String InstanceName { get; set; }

    public String DisplayName { get; set; }
   
    public String DisplayType { get; set; }

    public override String ToString()
    {
        return String.Format(@"{0}\{1}\{2}\{3}", MachineName ?? ".", CategoryName, CounterName, InstanceName);
    }
}

Dapper也可以加載填充嵌套對(duì)象，考慮這樣一種情形，考慮到新聞的類別屬性，返回類別對(duì)象。

1,在填充嵌套對(duì)象的時(shí)候，只好執(zhí)行ToList<>方法，否則回報(bào)ExecuteReader 要求已打開且可用的連接。連接的當(dāng)前狀態(tài)為已關(guān)閉,而單個(gè)對(duì)象不會(huì)報(bào)錯(cuò)，估計(jì)是using結(jié)束后關(guān)閉了連接，而嵌套對(duì)象在map的時(shí)候又執(zhí)行了ExecuteReader，只好在using結(jié)束之前返回list集合。
2,嵌套對(duì)象的參數(shù)是比較多的，主要是前兩個(gè)參數(shù)，其它參數(shù)沒用可以設(shè)置為null。特別要注意的是splitOn,這個(gè)參數(shù)不能為空，否則會(huì)報(bào)對(duì)象為引用的錯(cuò)誤。【splitOn參數(shù)的意思是讀取第二個(gè)對(duì)象的的分割列，從哪個(gè)列起開始讀取第二個(gè)對(duì)象，如果表里的自增長(zhǎng)列都為Id,可以設(shè)置這個(gè)參數(shù)為”Id”】.

Execute方法：
正如Query方法是檢索數(shù)據(jù)的，Execute方法不會(huì)檢索數(shù)據(jù)，它與Query方法非常相似，但它總返回總數(shù)（受影響的行數(shù)）,而不是一個(gè)對(duì)象集合【如：insert update和delete】.

private void SaveServiceSnapshots(IEnumerable<ServiceCounterSnapshot> snapshots)
        {
            using (var conn = new SqlConnection(ConfigurationManager.ConnectionStrings["SqlDiagnosticsDb"].ConnectionString))
            {
                conn.Open();
                foreach (var snapshot in snapshots)
                {
                    // insert new snapshot to the database
                   conn.Execute(
    @"insert into service_counter_snapshots(ServiceCounterId,SnapshotMachineName,CreationTimeUtc,ServiceCounterValue) values (
        @ServiceCounterId,@SnapshotMachineName,@CreationTimeUtc,@ServiceCounterValue)", snapshot);
                }

            }
        }

ServiceCounterSnapshot的定義如下：

public class ServiceCounterSnapshot
{
    public int Id { get; set; }

    public int ServiceCounterId { get; set; }

    /// <summary>
    /// Machine on which the snapshot was taken.
    /// </summary>
    public String SnapshotMachineName { get; set; }

    public DateTime CreationTimeUtc { get; set; }

    public float? ServiceCounterValue { get; set; }
}

A Look at Dapper.NET

關(guān)于Dapper的一些使用和擴(kuò)展的例子

給力分享新的ORM => Dapper