I have this line:
GlobalConfiguration.Configuration.Formatters.Add(New ExcelMediaTypeFormatter(Of Classification)(Function(t) New ExcelRow(ExcelCell.Map(t.ChemicalAbstractService), ExcelCell.Map(t.Substance), ExcelCell.Map(t.Columns("Classifidcation")), ExcelCell.Map(t.Columns("Classification"))), Function(format) "excel"))
It works fine and creates a excelfile from my web api.
I have several subclasses that inherits this Classification class and I want to make a mediaformatter for each subclass for getting specific columns in the excelformatter. The problems is that if I do like this:
GlobalConfiguration.Configuration.Formatters.Add(New ExcelMediaTypeFormatter(Of CustomClassification)(Function(t) New ExcelRow(ExcelCell.Map(t.ChemicalAbstractService), ExcelCell.Map(t.Substance), ExcelCell.Map(t.Columns("Classifidcation")), ExcelCell.Map(t.Columns("Classification"))), Function(format) "excel"))
Then it doesn't work at all. It just generates xml from the standard formatter instead. How can I make it react to a subclass, when the web api returns a
IQueryable(Of Classification)
The formatter:
public class ExcelMediaTypeFormatter<T> : BufferedMediaTypeFormatter
{
private const string ContentType = "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet";
private readonly Func<T, ExcelRow> builder;
public ExcelMediaTypeFormatter(Func<T, ExcelRow> value)
{
builder = value;
SupportedMediaTypes.Add(new MediaTypeHeaderValue(ContentType));
}
public ExcelMediaTypeFormatter(Func<T, ExcelRow> value, params Func<object, string>[] type)
: this(value)
{
foreach (var mediaTypeMapping in type) {
this.MediaTypeMappings.Add(Map(mediaTypeMapping));
}
}
public override bool CanWriteType(Type type)
{
return type == typeof(IQueryable<T>) || type == typeof(T);
}
public override bool CanReadType(Type type)
{
return false;
}
public override void WriteToStream(Type type, object value, Stream writeStream, HttpContent content)
{
using (Stream ms = new MemoryStream()) {
using (var book = new ClosedXML.Excel.XLWorkbook()) {
var sheet = book.Worksheets.Add("sample");
ICollection<T> rows = type == typeof(IQueryable<T>) ? ((IQueryable<T>)value).ToList() : new List<T>() { (T)value };
for (var r = 0; r < rows.Count; r++) {
var result = builder((T)rows.ElementAt(r));
for (var c = 0; c < result.Count(); c++) {
if (result.ElementAt(c) != null)
sheet.Cell(r + 2, c + 1).Value = result.ElementAt(c).Value.ToString();
}
}
sheet.Columns().AdjustToContents();
book.SaveAs(ms);
byte[] buffer = new byte[ms.Length];
ms.Position = 0;
ms.Read(buffer, 0, buffer.Length);
writeStream.Write(buffer, 0, buffer.Length);
}
}
}
CanWriteType will return false, because T is CustomClassification and type is Classification. Your formatter will not be used if it returns false.
Because a Classification is not necessarily a CustomClassification this can't work.
To achieve what you want, you need to change your implementation a bit.
Your ExcelMediaTypeFormatter will no longer be generic. And it will not get passed one Func but a list of IRowsBuilder instances. These will be used in the WriteToStream method to select the correct builder:
public interface IRowsBuilder
{
bool CanBuildFor(Type type);
IEnumerable<Type> SupportedTypes { get; }
ExcelRow BuildRow(object value);
}
public class RowsBuilder<T> : IRowsBuilder where T : Classification
{
Func<T, ExcelRow> _builder;
public RowsBuilder(Func<T, ExcelRow> builder)
{
if(builder == null) throw new ArgumentNullException("builder");
_builder = builder;
}
public bool CanBuildFor(Type type)
{
return type.IsSubclassOf(typeof(T));
}
public IEnumerable<Type> SupportedTypes
{
get { yield return typeof(T); }
}
public ExcelRow BuildRow(object value)
{
if(!CanBuildFor(value.GetType()))
throw new ArgumentException();
return _builder((T)value);
}
}
public class ExcelMediaTypeFormatter : BufferedMediaTypeFormatter
{
private readonly ILookup<Type, IRowsBuilder> _builder;
public ExcelMediaTypeFormatter(IEnumerable<IRowsBuilder> builder)
{
_builder = builder.SelectMany(x => builder.SupportedTypes
.Select(y => new
{
Type = y,
Builder = x
}))
.ToLookup(x => x.Type, x => x.Builder);
}
public override bool CanWriteType(Type type)
{
return type == typeof(IQueryable<Classification>) ||
type == typeof(Classification);
}
// ...
public override void WriteToStream(Type type, object value,
Stream writeStream, HttpContent content)
{
// ...
List<Classification> rows;
if(type == typeof(IQueryable<Classification>))
rows = ((IQueryable<Classification>)value).ToList();
else
rows = new List<Classification> { (Classification)value };
for (var r = 0; r < rows.Count; r++)
{
var value = rows.ElementAt(r);
var builder = _builder[value.GetType()];
var result = builder(value);
// ...
}
}
}
You would now only register one ExcelMediaTypeFormatter with all the builders:
var customBuilder = new RowsBuilder<CustomClassification>(
t => new ExcelRow(ExcelCell.Map(t.ChemicalAbstractService),
ExcelCell.Map(t.Substance),
ExcelCell.Map(t.Columns("Classifidcation")),
ExcelCell.Map(t.Columns("Classification"))));
var builders = new List<IRowsBuilder>();
builder.Add(customBuilder);
builder.Add(someOtherBuilder);
var excelFormatter = new ExcelMediaTypeFormatter(builders, format => "excel");
GlobalConfiguration.Configuration
.Formatters
.Add(excelFormatter);