如何在不使用 class 映射的情况下控制 CsvHelper 写入 CSV 文件头的顺序？

Question

I have the following method to write dynamic CSV file records:

 public byte[] BuildProductsFile(List<object> records)
    {
      var firstRow = records.FirstOrDefault();
      var columnHeaders = ((IDictionary<string, object>) firstRow).Keys.ToList();

      using var memoryStream = new MemoryStream();
      using (var streamWriter = new StreamWriter(memoryStream))
      {
        using var csvWriter = new CsvWriter(streamWriter);
        csvWriter.WriteRecords(records);

      }
      return memoryStream.ToArray();
    }

When I do WriteRecords, it changes header names to alphabetic order which I don't want since afterwards my rows correspond to incorrect headers. I can't use a class to specify header names because they will be different depending on different tables which user would like to get.

My question is can I write the header names in the correct sequence, which I can get from

var columnHeaders = ((IDictionary<string, object>) firstRow).Keys.ToList();

Alternatively, is there a way to disable alphabetical order header placing?

Answer 1

You must be using a version of CsvHelper between 10.0.0 and 12.0.0 . Between these two versions, CsvWriter.WriteRecords() would write ExpandoObject properties in alphabetical order. Upgrade to a later version (or downgrade to an earlier version) to eliminate this behavior.

For confirmation, see the change log :

10.0.0

Features:

• Write ExpandoObject and IDynamicMetaObjectProvider object properties in ascending order to ensure order of property creation doesn't matter.

---

12.0.0

Features

• Added config option for sorting dynamic object properties when writing. Defaults to property value set order.

Breaking Changes

• Added IComparer<string> IWriterConfiguration.DynamicPropertySort .
• Added IComparer<string> Configuration.DynamicPropertySort .

See When writing dynamic object order of property assignments is significant #1037 for a discussion of why this happened.

A demo of CsvHelper failing in version 11 can be found here: demo #1 .

A demo of CsvHelper working as desired in the most recent version, version 26, can be found here: demo #2 .

And if you really need to write your CSV columns in an order specified by a sequence of strings, you can use CsvConfiguration.DynamicPropertySort mentioned above:

class OrderComparer : IComparer<string>
{
    // Note this comparer assumes that all strings to be compared are present in the incoming collection of strings, and will throw an exception if not.
    // If this is not desired, enhance as required.
    readonly Dictionary<string, int> orders;
    public OrderComparer(IEnumerable<string> orderedHeaders) => orders = orderedHeaders.Select((i, s) => (i, s)).ToDictionary(p => p.i, p => p.s);
    public int Compare(string x, string y) =>  orders[x] - orders[y];
}

public static  byte[] BuildProductsFile(List<object> records, IEnumerable<string> orderedHeaders) =>
    BuildProductsFile(records, new OrderComparer(orderedHeaders));

public static  byte[] BuildProductsFile(List<object> records, IComparer<string> dynamicPropertySort)
{
    using var memoryStream = new MemoryStream();
    using (var streamWriter = new StreamWriter(memoryStream))
    {
        var config = new CsvConfiguration(CultureInfo.InvariantCulture)
        {
            DynamicPropertySort = dynamicPropertySort,
        };
        using var csvWriter = new CsvWriter(streamWriter, config); 
        csvWriter.WriteRecords(records);

    }
    return memoryStream.ToArray();  
}

Demo of DynamicPropertySort here: demo #3 .