[Yugong Series] April 2023 .NET CORE Tool Case - .NET Core Using ExcelMapper

foreword

ExcelMapper is an open source component based on the MIT protocol, which reads and writes Excel by manipulating the data model in C#. It provides a very neat API, even reading or writing Excel data with one line of code.

Core functions

• Read and write Excel files
• Use a purely managed NPOI library instead of the Jet database engine (NPOI User Group)
• Map to an Excel file with a header row (column names) or column index (no header row)
• Map nested objects (parent/child objects)
• Optionally skip blank lines while reading
• Preserve formatting when saving back to file
• (Optional) Let the mapper keep track of the object
• Map columns to properties by convention, property, or method call
• Use custom or built-in data formats for numeric and datetime columns
• Map formula or formula result based on attribute type
• Mapping JSON
• get/save dynamic object
• usage record
• Provide a custom object factory

GitHub URL: github.com/mganss/Exce…

1. .NET Core uses ExcelMapper

1. Use Nuget to search and install ExcelMapper

2. Read the object from the Excel file

var products = new ExcelMapper("products.xlsx").Fetch<Product>();
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public class Product
{
  public string Name { get; set; }
  public int NumberInStock { get; set; }
  public decimal Price { get; set; }
}
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3. Attribute mapping

3.1 Mapping to specific column names

public class Product
{
  public string Name { get; set; }
  [Column("Number")]
  public int NumberInStock { get; set; }
  public decimal Price { get; set; }
}
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3.2 Mapping to column index

public class Product
{
    [Column(1)]
    public string Name { get; set; }
    [Column(Letter="C")]
    public int NumberInStock { get; set; }
    [Column(4)]
    public decimal Price { get; set; }
}

var products = new ExcelMapper("products.xlsx") { HeaderRow = false }.Fetch<Product>();
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Note that column indexes do not need to be contiguous. When mapping to a column index, each property needs to be explicitly mapped through a property or method. You can combine column indices with column names to specify an explicit column order while still using the header row.

3.3 Mapping by method call

In addition to adding features to entity classes, ExcelMapper also supports manual mapping using code, as follows

var excel = new ExcelMapper("products.xls");
excel.AddMapping<Product>("Number", p => p.NumberInStock);
excel.AddMapping<Product>(1, p => p.NumberInStock);
excel.AddMapping(typeof(Product), "Number", "NumberInStock");
excel.AddMapping(typeof(Product), ExcelMapper.LetterToIndex("A"), "NumberInStock");
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3.4 Multiple mappings

You can map a single column to multiple properties, but you need to understand what should happen when mapping from the object back to Excel. To specify a single property to map back to Excel, add a property that maps to all other properties of the same column. Alternatively, this method can be used when mapping via method calls.

public class Product
{
    public decimal Price { get; set; }
    [Column("Price", MappingDirections.ExcelToObject)]
    public string PriceString { get; set; }
}

// or

excel.AddMapping<Product>("Price", p => p.PriceString).FromExcelOnly();
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Column attributes are inherited by default, and adding attributes to attributes in Base would result in multiple mappings and derived classes for a single overriding attribute. To prevent this, set the property to false on the property in the base class.

3.5 动态映射

你可以不定义实体类，直接使用 dynamic 类型获取数据，如下

var products = new ExcelMapper("products.xlsx").Fetch(); // -> IEnumerable<dynamic>
products.First().Price += 1.0;
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3.6 忽略属性

public class Product
{
    public string Name { get; set; }
    [Ignore]
    public int Number { get; set; }
    public decimal Price { get; set; }
}

// or

var excel = new ExcelMapper("products.xlsx");
excel.Ignore<Product>(p => p.Price);
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3.7 特定数据格式

public class Product
{
    [DataFormat(0xf)]
    public DateTime Date { get; set; }

    [DataFormat("0%")]
    public decimal Number { get; set; }
}
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更多属性使用清参考官网

4.写入 Excel 文件

1、纯写入

var products = new List<Product>
{
    new Product { Name = "Nudossi", NumberInStock = 60, Price = 1.99m },
    new Product { Name = "Halloren", NumberInStock = 33, Price = 2.99m },
    new Product { Name = "Filinchen", NumberInStock = 100, Price = 0.99m },
};

new ExcelMapper().Save("products.xlsx", products, "Products");
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2、读取写入

var products = new ExcelMapper("products.xlsx").Fetch<Product>().ToList();
products[1].Price += 1.0m;
excel.Save("products.out.xlsx");
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3、JSON 支持

你可以非常方便的把 Excel 中的数据映射到 Json 类型中，通过使用 Json 特性或者 AsJson 方法，如下

public class ProductJson
{
    [Json]
    public Product Product { get; set; }
}

// or

var excel = new ExcelMapper("products.xls");
excel.AddMapping<ProductJson>("Product", p => p.Product).AsJson();
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