Question

我有以下代码。似乎所有20个对象都被创建了然后第一个foreach正常工作并遍历所有20 使用linq的第二个示例也很有效。

然后是否可以使用ReportKey之类的属性仅定位其中一个对象，并为该对象运行方法RunThisReport？或者，因为我使用了类型IEnumerable<>，我走了一条死路？

static void Main(string[] args) {

    var models = SelectReports("SELECT * FROM 20RecordTable");

     //1.running the method for each
    foreach(myReport x in models) {
        Console.WriteLine("Doubled key:{0}",  x.myReportKeyDoubled().ToString());
    }

    //2.linq sample
    var result = from sample in models
                    select sample.ReportName;
    foreach(string x in result) {
        Console.WriteLine(Convert.ToString(x));
    }

    //3. target a single report say reportKey 512 and run the method RunThisReport?

    Console.WriteLine("Press [enter] to exit");
    Console.Read();
}

static IEnumerable<myReport> SelectReports(string myCommandText) {

    var connectionString = ConfigurationManager.ConnectionStrings["xxx"].ConnectionString;
    using(var conn = new SqlConnection(connectionString))
    using(var cmd = conn.CreateCommand()) {
        conn.Open();
        cmd.CommandText = myCommandText;
        using(var reader = cmd.ExecuteReader()) {

            while(reader.Read()) {
                yield return new myReport {

                    ReportKey = reader.GetInt32(reader.GetOrdinal("ReportKey")),
                    ReportName  = reader.GetString(reader.GetOrdinal("ReportName")),
                    ReportDescription  = reader.GetString(reader.GetOrdinal("ReportDescription")),
                    ReportTechDescription = reader.GetString(reader.GetOrdinal("ReportTechDescription "))

                };
            }
        }
    }
}

public class myReport {

    public int ReportKey { get; set; }
    public string ReportName { get; set; }
    public string ReportDescription { get; set; }
    public string ReportTechDescription { get; set; }

    public int myReportKeyDoubled() {
        return ReportKey*2;
    }
    public string RunThisReport(){
        return this.ReportName + " needs to be run via" + this.ReportTechDescription;
    }         
}

Answer 1

 var report = models.SingleOrDefault(m => m.ReportKey == 512);

 if (report != null)
     report.RunThisReport();

或者用理解语法（丑陋，是吗？）：

var report = (from m in models
              where m.ReportKey == 512
              select m).SingleOrDefault();

BTW与Dapper您的代码将如下所示：

static IEnumerable<myReport> SelectReports(string myCommandText) 
{    
    var connectionString = ConfigurationManager.ConnectionStrings["xxx"].ConnectionString;
    using(var conn = new SqlConnection(connectionString))
    {
        conn.Open();
        return conn.Query<myReport>(myCommandText);    
    }
}

Dapper可通过NuGet获得。在使用ADO.NET时，这是我的选择

Answer 2

models.First(x => x.ReportKey == 42).RunThisReport();

Answer 3

如果我正确地阅读此内容，那么您正在努力使用LINQ来获取对象。这里最简单的方法是使用LINQ扩展方法。我相信这就是你要找的东西：

models.First(i => i.ReportKey == yourReportKey).RunThisReport();

或者澄清这里发生了什么：

// Get the report that matches the key
myReport report = models.First(i => i.ReportKey == "YOUR-KEY-VALUE");

// Call RunThisReport for that report.
report.RunThisReport();

这也适用于收藏：

models.Where(i => i.ReportKey == yourReportKey).ForEach(report => report.RunThisReport());

希望有所帮助！如果没有，请澄清你的问题，我很乐意提供帮助。

使用IEnumerable时定位单个报告

3 个答案: