在 F# 中使用 SqlDataReader [英] Use SqlDataReader in F#

问题描述

在 C# 中，我使用 sql 脚本将数据添加到列表中，其中 T 将是一个字段/属性映射到 sql 脚本的类.

In C# I use sql scripts to add data into a List where T would be a class with fields/properties mapped to the sql script.

我怎么能在 F# 中做到这一点?这篇文章以标准方式使用存储过程.

How could I do this in F#? This piece uses a stored procedure in the standard way.

using (conn)
{
    conn.Open();
    using (SqlCommand cmd = new SqlCommand("dbo.query_here", conn))
    {
    cmd.CommandText = "dbo.query_here";
    cmd.CommandType = System.Data.CommandType.StoredProcedure;
    cmd.CommandTimeout = 600;
    cmd.Parameters.Add(new SqlParameter("@x1", Convert.ToString(x)));
    cmd.Parameters.Add(new SqlParameter("@y1", y));
    cmd.Parameters.Add(new SqlParameter("@z1", z));
    SqlDataReader reader = cmd.ExecuteReader();
    while (reader.Read())
    {
        MyListOfClasses.Add(new MyDataClass(reader.GetInt32(reader.GetOrdinal("x"))           
                                            reader.GetDouble(reader.GetOrdinal("y")),
                                            reader.GetDouble(reader.GetOrdinal("a")),
                                            reader.GetDouble(reader.GetOrdinal("b"))));
    }
    reader.Close();
}
conn.Close();

我意识到 F# 可能不像这样直接，但我需要以类似的方式将这些数据放入 F# 列表中.也更喜欢本质上没有功能并遵循与 C# 代码类似的模式的建议.

I realise F# is not quite as straight forward perhaps as this, but I need to get this data into F# lists in a similar way. Also would prefer suggestions that were not functional in nature and followed a similar pattern to C# code.

在前一个线程中，有人建议使用记录，但这仍然与 SqlDataReader 无关.最好有一个类列表，这样我就可以在每个项目上使用 getter 和 setter.

In a previous thread someone suggested using records, but still this was not in relation to SqlDataReader. It would be preferable to have a list of classes so I can use getters and setters on each item.

我应该在为什么不直接使用 C#"的不可避免的注释之前添加.显然我可以使用 C#，但我正在探索用 F# 编写算法的可能性，为此我需要从 SQL Server 获取原始数据.

I should add before the inevitable comments of "why not just use C#". Well obviously I can use C#, but I am exploring possibilities of writing algorithms in F# and to do that I need to get my raw data from SQL Server.

推荐答案

如果你想在 F# 列表中返回 results，列表理解适合在这里使用.并且使用 use 关键字，您不需要显式处置对象.

If you would like to return results in F# list, list comprehension is suitable to use here. And with use keyword, you don't need to explicitly dispose objects.

use conn = (* Initialize sql connection here *)
conn.Open()
use cmd = new SqlCommand("dbo.query_here", conn)
cmd.CommandText <- "dbo.query_here"
cmd.CommandType <- System.Data.CommandType.StoredProcedure
cmd.CommandTimeout <- 600
cmd.Parameters.Add(new SqlParameter("@x1", Convert.ToString(x)))
cmd.Parameters.Add(new SqlParameter("@y1", y))
cmd.Parameters.Add(new SqlParameter("@z1", z))
use reader = cmd.ExecuteReader()
let results =
 [ while reader.Read() do
    yield new MyDataClass(reader.GetInt32(reader.GetOrdinal("x")),           
                          reader.GetDouble(reader.GetOrdinal("y")),
                          reader.GetDouble(reader.GetOrdinal("a")),
                          reader.GetDouble(reader.GetOrdinal("b"))) ]

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