.NET how to output csv from enumeration of anonymous type?

Question

Using FileHelpers, I decorated a class with [DelimitedRecord(",")] and was going to output an enumeration of objects of that type as CSV. But, it didn't work because my class inherits from ActiveRecordLinqBase<T>, which caused some problems.

So, I was wondering if I could just select an enumeration of anonymous types and somehow have filehelpers generate csv from that. I don't like having to define a class just for FileHelpers to output csv.

I would be open to using another csv library, but FileHelpers is proven.

EDIT

@Foovanadil: This would be the sort of thing I am trying to do:

CreateCSV(MyCollection.Select(x=>new{
    x.Prop1,
    x.Prop2,
    x.Prop3
}));

Gives you:

Prop1,Prop2,Prop3
val1a,val2a,val3a
val1b,val2b,val3b
etc.....

Answer 1

Your CreateCSV list would look something like this:

static StringBuilder CreateCSV<T>( IEnumerable<T> data )
{
    StringBuilder builder = new StringBuilder();
    var properties = typeof( T ).GetProperties();

    foreach ( var prop in properties )
    {   
        builder.Append( prop.Name ).Append( ", " );
    }

    builder.Remove( builder.Length - 2, 2 ).AppendLine();

    foreach ( var row in data )
    {
        foreach ( var prop in properties )
        {
            builder.Append( prop.GetValue( row, null ) ).Append( ", " );
        }

        builder.Remove( builder.Length - 2, 2 ).AppendLine();
    }

    return builder;
}

Answer 2

LINQ To CSV worked great for me.

Here's an example of how I am using it:

protected void Page_Load(object sender, EventArgs e)
{
    var courseId = int.Parse(Request["id"]);
    var course = Course.Queryable.Single(x => x.Id == courseId);
    Response.ContentType = "text/csv";
    Response.AddHeader("Content-Disposition", string.Format("attachment;filename=\"{0}.csv\";", course.Code));

    var csvContext = new LINQtoCSV.CsvContext();
    var writer = new System.IO.StreamWriter(Response.OutputStream);
    csvContext.Write(course.Registrations.Select(x => new
    {
        x.StudentId,
        x.Name,
        x.EmailAddress,
        x.MoodleUsername,
        x.Age,
        x.Is65OrOlder,
        x.CertificationAndRank,
        x.Citizenship,
        x.DateOfBirth,
        x.DepartmentName,
        x.StationNumber,        
        x.EmploymentStatus,
        x.HighestEducationLevel
    }), writer);        

    writer.Dispose();
}

UPDATE

There are some downsides to the approach above:

• The column order in the csv file is unpredictable. It doesn't follow the order of the property definitions in the anonymous type.
• Column headers come from the property names which aren't always what is is desired.

So, I decided I would create a class just for the CSV records, which didn't end up being any more work than the anonymous type did. I used Auto Mapper to flatten my source class and populate the property values of the CSV class. I also decided to compare FileHelpers to Linq To CSV. Linq To CSV was the obvious winner, in my situation:

• L2CSV allowed you apply an attribute to each property in the class for defining the column order, column header title, and conversion formats.
• FHs would only let you supply a conversion format for each field. The column order depended on the order of the properties as they are defined in the class.
• FHs would not infer a column header from the property name nor let you supply one. You could supply a literal string as the header for the CSV file, which is no good: The delimiter is built into the literal string; the column titles' order is not synced with the order of the properties.

I hope these findings are useful. Here is my new code:

// CSV Class

public class CsvRegistration
{
    [CsvColumn(FieldIndex = 0)]
    public string Name { get; set; }

    [CsvColumn(FieldIndex = 1, Name = "Student Id")]
    public int StudentId { get; set; }

    [CsvColumn(FieldIndex = 2, Name = "Email Address")]
    public string EmailAddress { get; set; }

    [CsvColumn(FieldIndex = 3, Name = "Moodle Username")]
    public string MoodleUsername { get; set; }

    [CsvColumn(FieldIndex = 4, Name = "Dept. Name")]
    public string DepartmentName { get; set; }

    [CsvColumn(FieldIndex = 5, Name = "Station #")]
    public string StationNumber { get; set; }

    [CsvColumn(FieldIndex = 6, Name = "Highest Education Level")]
    public string HighestEducationLevel { get; set; }

    [CsvColumn(FieldIndex = 7, Name = "Certification/Rank")]
    public string CertificationAndRank { get; set; }

    [CsvColumn(FieldIndex = 8, Name = "Employment Status")]
    public string EmploymentStatus { get; set; }

    [CsvColumn(FieldIndex = 9, Name = "Registration Date")]
    public DateTime RegistrationDate { get; set; }

    [CsvColumn(FieldIndex = 10, Name = "Date of Birth")]
    public DateTime DateOfBirth { get; set; }

    [CsvColumn(FieldIndex = 11)]
    public int Age { get; set; }

    [CsvColumn(FieldIndex = 12)]
    public string Citizenship { get; set; }

    [CsvColumn(FieldIndex = 13)]
    public string Race { get; set; }

    [CsvColumn(FieldIndex = 14)]
    public string Ethnicity { get; set; }

    [CsvColumn(FieldIndex = 15, Name = "Home Address")]
    public string HomeAddressLine1 { get; set; }

    [CsvColumn(FieldIndex = 16, Name = "City")]
    public string HomeAddressCity { get; set; }

    [CsvColumn(FieldIndex = 17, Name = "State")]
    public string HomeAddressState { get; set; }

    [CsvColumn(FieldIndex = 18, Name = "Zip")]
    public string HomeAddressZip { get; set; }

    [CsvColumn(FieldIndex = 19, Name = "County")]
    public string HomeAddressCounty { get; set; }

    [CsvColumn(FieldIndex = 20, Name = "Home Phone")]
    public string HomePhone { get; set; }

    [CsvColumn(FieldIndex = 21, Name = "Work Phone")]
    public string WorkPhone { get; set; }
}


// ASPX page to serve csv file

protected void Page_Load(object sender, EventArgs e)
{
    var courseId = int.Parse(Request["id"]);
    var course = Course.Queryable.Single(x => x.Id == courseId);
    Response.ContentType = "text/csv";
    Response.AddHeader("Content-Disposition", string.Format("attachment;filename=\"{0}.csv\";", course.Code));

    using (var writer = new System.IO.StreamWriter(Response.OutputStream))
    {
        var registrations = Mapper.Map<IEnumerable<Registration>, IEnumerable<CsvRegistration>>(course.Registrations);
        var cc = new LINQtoCSV.CsvContext();
        cc.Write(registrations, writer);
    }
}