CsvHelper是一个用于读写CSV（逗号分隔值）文件的开源.NET库。它提供了简单而强大的API，使得处理CSV文件变得轻而易举。本文将详细介绍CsvHelper的使用方法，并提供多个实用的例子。

安装

首先，通过NuGet包管理器安装CsvHelper：

C#
Install-Package CsvHelper

基本用法

读取CSV文件

假设我们有一个名为people.csv的文件，内容如下：

text
Name,Age,City
John Doe,30,New York
Jane Smith,25,London
Mike Johnson,35,Paris

我们可以使用以下代码读取这个文件：

C#
using System;
using System.Globalization;
using System.IO;
using CsvHelper;

public class Person
{
    public string Name { get; set; }
    public int Age { get; set; }
    public string City { get; set; }
}

class Program
{
    static void Main(string[] args)
    {
        using (var reader = new StreamReader("people.csv"))
        using (var csv = new CsvReader(reader, CultureInfo.InvariantCulture))
        {
            var records = csv.GetRecords<Person>();
            foreach (var record in records)
            {
                Console.WriteLine($"{record.Name} is {record.Age} years old and lives in {record.City}.");
            }
        }
    }
}

写入CSV文件

现在，让我们创建一个新的CSV文件：

C#
using System.Collections.Generic;
using System.Globalization;
using System.IO;
using CsvHelper;

public class Product
{
    public string Name { get; set; }
    public decimal Price { get; set; }
    public int Quantity { get; set; }
}

class Program
{
    static void Main(string[] args)
    {
        var products = new List<Product>
        {
            new Product { Name = "Apple", Price = 0.5m, Quantity = 100 },
            new Product { Name = "Banana", Price = 0.3m, Quantity = 150 },
            new Product { Name = "Orange", Price = 0.4m, Quantity = 80 }
        };

        using (var writer = new StreamWriter("products.csv"))
        using (var csv = new CsvWriter(writer, CultureInfo.InvariantCulture))
        {
            csv.WriteRecords(products);
        }
    }
}

高级用法

自定义映射

有时，CSV文件的列名可能与我们的类属性名不匹配。我们可以使用自定义映射来解决这个问题：

C#
using CsvHelper;
using CsvHelper.Configuration;
using System;
using System.Globalization;
using System.IO;
using System.Collections.Generic;

public class Person
{
    public string Name { get; set; }
    public int Age { get; set; }
    public string City { get; set; }
}

public class PersonMap : ClassMap<Person>
{
    public PersonMap()
    {
        Map(m => m.Name).Name("FullName");
        Map(m => m.Age).Name("YearsOld");
        Map(m => m.City).Name("Location");
    }
}

class Program
{
    static void Main(string[] args)
    {
        string filePath = "people_custom.csv";

        // 首先创建一些示例数据并写入CSV文件  
        CreateSampleCsvFile(filePath);

        // 然后读取CSV文件  
        List<Person> people = ReadCsvFile(filePath);

        // 打印读取的数据  
        foreach (var person in people)
        {
            Console.WriteLine($"Name: {person.Name}, Age: {person.Age}, City: {person.City}");
        }
    }

    static void CreateSampleCsvFile(string filePath)
    {
        var records = new List<Person>
        {
            new Person { Name = "John Doe", Age = 30, City = "New York" },
            new Person { Name = "Jane Smith", Age = 25, City = "Los Angeles" },
            new Person { Name = "Bob Johnson", Age = 45, City = "Chicago" }
        };

        using (var writer = new StreamWriter(filePath))
        using (var csv = new CsvWriter(writer, CultureInfo.InvariantCulture))
        {
            csv.Context.RegisterClassMap<PersonMap>();
            csv.WriteRecords(records);
        }

        Console.WriteLine("Sample CSV file created.");
    }

    static List<Person> ReadCsvFile(string filePath)
    {
        using (var reader = new StreamReader(filePath))
        using (var csv = new CsvReader(reader, CultureInfo.InvariantCulture))
        {
            csv.Context.RegisterClassMap<PersonMap>();
            return csv.GetRecords<Person>().ToList();
        }
    }
}

忽略某些字段

如果我们只想读取或写入特定的字段，可以使用Ignore()方法：

C#
public class PersonMap : ClassMap<Person>
{
    public PersonMap()
    {
        Map(m => m.Name);
        Map(m => m.Age);
        Map(m => m.City).Ignore();
    }
}

处理日期时间

CsvHelper可以自动处理日期时间的转换，但有时我们可能需要指定特定的格式：

C#
using CsvHelper;
using CsvHelper.Configuration;
using System;
using System.Collections.Generic;
using System.Globalization;
using System.IO;

public class Event
{
    public string Name { get; set; }
    public DateTime Date { get; set; }
}

public class EventMap : ClassMap<Event>
{
    public EventMap()
    {
        Map(m => m.Name);
        Map(m => m.Date).TypeConverterOption.Format("yyyy-MM-dd");
    }
}

class Program
{
    static void Main(string[] args)
    {
        string filePath = "events.csv";

        // 写入CSV文件  
        WriteEventsToCSV(filePath);

        // 读取CSV文件  
        List<Event> events = ReadEventsFromCSV(filePath);

        // 打印读取的数据  
        foreach (var evt in events)
        {
            Console.WriteLine($"Event: {evt.Name}, Date: {evt.Date:yyyy-MM-dd}");
        }
    }

    static void WriteEventsToCSV(string filePath)
    {
        using (var writer = new StreamWriter(filePath))
        using (var csv = new CsvWriter(writer, CultureInfo.InvariantCulture))
        {
            csv.Context.RegisterClassMap<EventMap>();
            csv.WriteRecords(new List<Event>
            {
                new Event { Name = "Conference", Date = new DateTime(2023, 5, 15) },
                new Event { Name = "Workshop", Date = new DateTime(2023, 6, 1) }
            });
        }
        Console.WriteLine("CSV file written successfully.");
    }

    static List<Event> ReadEventsFromCSV(string filePath)
    {
        using (var reader = new StreamReader(filePath))
        using (var csv = new CsvReader(reader, CultureInfo.InvariantCulture))
        {
            csv.Context.RegisterClassMap<EventMap>();
            return csv.GetRecords<Event>().ToList();
        }
    }
}

处理枚举

CsvHelper可以很好地处理枚举类型：

C#
public enum Category
{
    Food,
    Electronics,
    Clothing
}

public class Product
{
    public string Name { get; set; }
    public Category Category { get; set; }
}

class Program
{
    static void Main(string[] args)
    {
        var products = new List<Product>
        {
            new Product { Name = "Apple", Category = Category.Food },
            new Product { Name = "Laptop", Category = Category.Electronics },
            new Product { Name = "T-Shirt", Category = Category.Clothing }
        };

        using (var writer = new StreamWriter("products_with_category.csv"))
        using (var csv = new CsvWriter(writer, CultureInfo.InvariantCulture))
        {
            csv.WriteRecords(products);
        }
    }
}

性能优化

对于大型CSV文件，我们可以使用GetRecords<T>()方法的延迟执行特性来提高性能：

C#
using (var reader = new StreamReader("large_file.csv"))
using (var csv = new CsvReader(reader, CultureInfo.InvariantCulture))
{
    foreach (var record in csv.GetRecords<Person>())
    {
        // 处理每条记录，而不是一次性加载所有记录到内存
        ProcessRecord(record);
    }
}

结论

CsvHelper是一个功能强大且灵活的库，可以大大简化CSV文件的处理过程。通过本文提供的示例，你应该能够处理大多数常见的CSV相关任务。无论是简单的读写操作，还是复杂的自定义映射和类型转换，CsvHelper都能够胜任。在处理数据导入导出、日志分析等涉及CSV格式的场景时，CsvHelper是一个值得考虑的工具。

希望这篇文章对你有所帮助，祝你在C#开发中使用CsvHelper愉快！