. net实体框架转换为CSV

本文关键字：CSV 转换 框架 实体 net | 更新日期: 2023-09-27 18:10:28

我使用最新的实体框架与DBContext。我有一个结果集，我想把它转换成逗号分隔的值。我做过类似的事情与数据表在VB数据表CSV提取。我已经让QuoteName方法工作了。我还获得了使用foreach工作的GetCSV方法的衍生物。问题是，它比DataTable的可比代码慢得多。所以我希望有人能给我一些建议。

    public static string GetCSV(this IQueryable entity)
    {
        if (entity == null)
        {
            throw new ArgumentNullException("entity");
        }
        Type T = entity.ElementType;
        var props = T.GetProperties(BindingFlags.Public | BindingFlags.Instance);
        string s = string.Empty;
        int iCols = props.Count();
        try
        {
            s += string.Join(",", (from int ii in Enumerable.Range(0, iCols)
                                   select props[ii].Name.QuoteName("[]")).ToArray());
            s += Environment.NewLine;
            foreach (var dr in entity)
            {
                s += string.Join(",", (from int ii in Enumerable.Range(0, iCols)
                                       select
                                           props[ii].GetValue(dr)
                                                    .ToString()
                                                    .QuoteName("'"'"", ",")).ToArray());
                s += Environment.NewLine;
            }
            s = s.TrimEnd(new char[] { (char)0x0A, (char)0x0D });
        }
        catch (Exception)
        {
            throw;
        }
        return s;
    }

. net实体框架转换为CSV

查看nuget包CsvHelper (http://nuget.org/packages/CsvHelper/)。

下面是来自https://github.com/JoshClose/CsvHelper/wiki/Basics

的用法示例
using (var csv = new CsvWriter( new StreamWriter( "Actors.csv" ) )) 
{
    csv.WriteRecords( actorsList );
}

不要使用字符串来创建文件。尝试使用StringBuilder类(http://msdn.microsoft.com/en-us/library/system.text.stringbuilder.aspx)

字符串是不可变的对象——也就是说，一旦字符串被创建，它就不能被改变。每次更改字符串(例如连接它)时，实际上都在创建一个全新的字符串。在这里使用字符串是非常低效的。

创建一个stringbuilder对象:

StringBuilder builder = new StringBuilder();
builder.Append("my data");

最后，调用

builder.ToString();

我从我弟弟那里得到了一些帮助。他说也要用StringBuilder。

这是代码答案:

    /// <summary>
    /// Quotes a string using the following rules:
    /// <list>
    /// <listheader>Rules</listheader>
    /// <item>if the string is not quoted and the string contains the separator string</item>
    /// <item>if the string is not quoted and the string begins or ends with a space</item>
    /// <item>if the string is not quoted and the string contains CrLf</item>
    /// </list>
    /// </summary>
    /// <param name="s">String to be quoted</param>
    /// <param name="quote">
    /// <list>
    /// <listheader>quote characters</listheader>
    /// <item>if len = 0 then double quotes assumed</item>
    /// <item>if len = 1 then quote string is doubled for left and right quote characters</item>
    /// <item>else first character is left quote, second character is right quote</item>
    /// </list>
    /// </param>
    /// <param name="sep">separator string to check against</param>
    /// <returns></returns>
    /// <remarks></remarks>
    public static string QuoteName(this string s, string quote = null, string sep = ",")
    {
        quote = quote == null ? "" : quote;
        switch (quote.Length)
        {
            case 0:
                quote = "'"'"";
                break;
            case 1:
                quote += quote;
                break;
        }
        // Fields with embedded sep are quoted
        if ((!s.StartsWith(quote.Substring(0, 1))) && (!s.EndsWith(quote.Substring(1, 1))))
            if (s.Contains(sep))
                s = quote.Substring(0, 1) + s + quote.Substring(1, 1);
        // Fields with leading or trailing blanks are quoted
        if ((!s.StartsWith(quote.Substring(0, 1))) && (!s.EndsWith(quote.Substring(1, 1))))
            if (s.StartsWith(" ") || s.EndsWith(" "))
                s = quote.Substring(0, 1) + s + quote.Substring(1, 1);
        // Fields with embedded CrLF are quoted
        if ((!s.StartsWith(quote.Substring(0, 1))) && (!s.EndsWith(quote.Substring(1, 1))))
            if (s.Contains(System.Environment.NewLine))
                s = quote.Substring(0, 1) + s + quote.Substring(1, 1);
        return s;
    }
    public static string GetCSV(this IQueryable entity)
    {
        if (entity == null)
        {
            throw new ArgumentNullException("entity");
        }
        Type T = entity.ElementType;
        var props = T.GetProperties(BindingFlags.Public | BindingFlags.Instance);
        var sb = new StringBuilder();
        int iCols = props.Count();
        try
        {
            sb.Append(string.Join(",", Enumerable.Range(0, iCols).Cast<int>().
                Select(ii => props[ii].Name.QuoteName("[]")).ToArray()));
            foreach (var dr in entity)
            {
                sb.AppendLine();
                sb.Append(string.Join(",", Enumerable.Range(0, iCols).Cast<int>().
                    Select(ii => props[ii].GetValue(dr).
                        ToString().QuoteName("'"'"", ",")).ToArray()));
            }
        }
        catch (Exception ex)
        {
            throw;
        }
        return sb.ToString();
    }
}

我希望这对别人有帮助

相关文章：