Adds mapping fields capability (#931)

* Refactoring of the mapping utilities, Attributes and Exceptions

- Added `MiniExcelAttributeBase` abstract class and made the other attributes inherit it
- Added feature for public fields of a class to be mapped alongside its properties if decorated with one of the attributes inheriting from afermonetioned base attribute
- Renamed all mapping utilities to reflect their mapping functionality and the custom accessors to reflect the shift from only properties to members
- Moved the `GetEmptyExpandoObject` methods to dedicated new class `ExpandoHelper`

* Refactoring of Importers

Refactored `OpenXmlImporter` and `CsvImporter` removing redundant logic and moving duplicate method in shared extension helper

* Added some tests for the field mapping feature and updated readme

* minor bugfixes

Author: michelebastione

README-V2.md

@@ -259,6 +259,30 @@ using var stream = File.OpenRead(path);
 var rows = importer.Query<UserAccount>(stream);
 ```
 
+Only public properties get mapped by default, but public fields can also be mapped if decorated with `MiniExcelColumnAttribute` or any of the other MiniExcel attributes:   
+```csharp
+public class UserAccount
+{
+    [MiniExcelColumn]
+    public Guid ID;
+    
+    public string Name { get; set; }
+    
+    [MiniExcelFormat("dd/MM/yyyy")]
+    public DateTime BoD;
+    
+    public int Age { get; set; }
+    
+    [MiniExcelColumnIndex(2)]
+    public bool VIP;
+    
+    public decimal Points { get; set; }
+}
+
+var importer = MiniExcel.Importers.GetOpenXmlImporter();
+var rows = importer.Query<UserAccount>(path);
+```
+
 #### 2. Execute a query and map it to a list of dynamic objects
 
 By default no header will be used and the dynamic keys will be `.A`, `.B`, `.C`, etc..:

src/MiniExcel.Core/Abstractions/IMiniExcelWriteAdapter.cs

@@ -3,13 +3,13 @@
 public interface IMiniExcelWriteAdapter
 {
     bool TryGetKnownCount(out int count);
-    List<MiniExcelColumnInfo>? GetColumns();
-    IEnumerable<IEnumerable<CellWriteInfo>> GetRows(List<MiniExcelColumnInfo> props, CancellationToken cancellationToken = default);
+    List<MiniExcelColumnMapping>? GetColumns();
+    IEnumerable<IEnumerable<CellWriteInfo>> GetRows(List<MiniExcelColumnMapping> props, CancellationToken cancellationToken = default);
 }
 
-public readonly struct CellWriteInfo(object? value, int cellIndex, MiniExcelColumnInfo prop)
+public readonly struct CellWriteInfo(object? value, int cellIndex, MiniExcelColumnMapping prop)
 {
     public object? Value { get; } = value;
     public int CellIndex { get; } = cellIndex;
-    public MiniExcelColumnInfo Prop { get; } = prop;
+    public MiniExcelColumnMapping Prop { get; } = prop;
 }

src/MiniExcel.Core/Abstractions/IMiniExcelWriteAdapterAsync.cs

@@ -2,6 +2,6 @@
 
 public interface IMiniExcelWriteAdapterAsync 
 {
-    Task<List<MiniExcelColumnInfo>?> GetColumnsAsync();
-    IAsyncEnumerable<CellWriteInfo[]> GetRowsAsync(List<MiniExcelColumnInfo> props, CancellationToken cancellationToken);
+    Task<List<MiniExcelColumnMapping>?> GetColumnsAsync();
+    IAsyncEnumerable<CellWriteInfo[]> GetRowsAsync(List<MiniExcelColumnMapping> props, CancellationToken cancellationToken);
 }

src/MiniExcel.Core/Attributes/MiniExcelAttributeBase.cs

@@ -0,0 +1,4 @@
+namespace MiniExcelLib.Core.Attributes;
+
+[AttributeUsage(AttributeTargets.Property | AttributeTargets.Field)]
+public abstract class MiniExcelAttributeBase : Attribute;

src/MiniExcel.Core/Attributes/MiniExcelColumnAttribute.cs

@@ -1,16 +1,15 @@
 namespace MiniExcelLib.Core.Attributes;
 
-[AttributeUsage(AttributeTargets.Property | AttributeTargets.Field)]
-public class MiniExcelColumnAttribute : Attribute
+public class MiniExcelColumnAttribute : MiniExcelAttributeBase
 {
     private int _index = -1;
     private string? _xName;
 
     public string? Name { get; set; }
-     public string[]? Aliases { get; set; } = [];
-     public string? Format { get; set; }
-     public bool Ignore { get; set; }
-    
+    public string[]? Aliases { get; set; } = [];
+    public string? Format { get; set; }
+    public bool Ignore { get; set; }
+
     internal int FormatId { get; private set; } = -1;
     public double Width { get; set; } = 8.42857143;
     public ColumnType Type { get; set; } = ColumnType.Value;
@@ -35,19 +34,19 @@ private void Init(int index, string? columnName = null)
         _index = index;
         _xName ??= columnName ?? CellReferenceConverter.GetAlphabeticalIndex(index);
     }
-    
-    public void SetFormatId(int formatId) =>  FormatId = formatId;
-}
 
-public enum ColumnType { Value, Formula }
+    public void SetFormatId(int formatId) => FormatId = formatId;
+}
 
 public class DynamicExcelColumn : MiniExcelColumnAttribute
 {
     public string Key { get; set; }
-    public Func<object, object>? CustomFormatter { get; set; }
+    public Func<object?, object?>? CustomFormatter { get; set; }
 
     public DynamicExcelColumn(string key)
     {
         Key = key;
     }
 }
+
+public enum ColumnType { Value, Formula }

src/MiniExcel.Core/Attributes/MiniExcelColumnIndexAttribute.cs

@@ -1,7 +1,6 @@
 namespace MiniExcelLib.Core.Attributes;
 
-[AttributeUsage(AttributeTargets.Property | AttributeTargets.Field)]
-public class MiniExcelColumnIndexAttribute : Attribute
+public class MiniExcelColumnIndexAttribute : MiniExcelAttributeBase
 {
     public int ExcelColumnIndex { get; set; }
     internal string? ExcelXName { get; set; }

src/MiniExcel.Core/Attributes/MiniExcelColumnNameAttribute.cs

@@ -1,7 +1,6 @@
 namespace MiniExcelLib.Core.Attributes;
 
-[AttributeUsage(AttributeTargets.Property | AttributeTargets.Field)]
-public class MiniExcelColumnNameAttribute(string columnName, string[]? aliases = null) : Attribute
+public class MiniExcelColumnNameAttribute(string columnName, string[]? aliases = null) : MiniExcelAttributeBase
 {
     public string ExcelColumnName { get; set; } = columnName;
     public string[] Aliases { get; set; } = aliases ?? [];

src/MiniExcel.Core/Attributes/MiniExcelColumnWidthAttribute.cs

@@ -1,7 +1,6 @@
 namespace MiniExcelLib.Core.Attributes;
 
-[AttributeUsage(AttributeTargets.Property | AttributeTargets.Field)]
-public class MiniExcelColumnWidthAttribute(double columnWidth) : Attribute
+public class MiniExcelColumnWidthAttribute(double columnWidth) : MiniExcelAttributeBase
 {
     public double ExcelColumnWidth { get; set; } = columnWidth;
 }

src/MiniExcel.Core/Attributes/MiniExcelFormatAttribute.cs

@@ -1,7 +1,6 @@
 namespace MiniExcelLib.Core.Attributes;
 
-[AttributeUsage(AttributeTargets.Property | AttributeTargets.Field)]
-public class MiniExcelFormatAttribute(string format) : Attribute
+public class MiniExcelFormatAttribute(string format) : MiniExcelAttributeBase
 {
     public string Format { get; set; } = format;
 }

src/MiniExcel.Core/Attributes/MiniExcelIgnoreAttribute.cs

@@ -1,7 +1,6 @@
 namespace MiniExcelLib.Core.Attributes;
 
-[AttributeUsage(AttributeTargets.Property | AttributeTargets.Field)]
-public class MiniExcelIgnoreAttribute(bool ignore = true) : Attribute
+public class MiniExcelIgnoreAttribute(bool ignore = true) : MiniExcelAttributeBase
 {
     public bool Ignore { get; set; } = ignore;
 }