Create default class map and map members to a Csv Field at run-time from collection of data

[jlw109]

Hi

I have a use-case for building ClassMap's at run-time from a collection of data that contains the property names for properties on classes used to represent data when reading or writing to csv.

I have been building class maps at run-time for classes without nested properties. But with complex properties (i.e. properties that are other reference types I define), not sure best way to build the ClassMap at run-time from a collection of data provided at run-time.

I put together a sample console app to demonstrate the use-case I'm trying to solve. Sample available at https://github.com/jlw109/CsvHelperDynamicClassMaps.git

Console app main method has three methods it calls.

        var dataFromExample1 = RunExampleWithStaticMapping();
        var dataFromExample2 = RunExampleWithStaticMappingUsingReferences();
        var dataFromExample3 = RunExampleWithDynamicMapping();

The first method called is an example with mapping the preferred way when you have nested properties and have defined a class map at compile time.

Second method called is an example with mapping when you have nested properties and have defined a class map at compile time, but using legacy References method.

Last method called is the use-case I am trying to solve.

See method in program.cs called BuildDynamicCsvClassMap(). Comment explains goals of method that is incomplete.

This relates a little to #1633

Update 1

I have committed changes that provides one solution to my use-case. I suspect this can be improved for reliability and performance.

The example demonstrates how to use CsvHelper to read or write a csv file using a class map that is constructed at run time from a collection of custom objects defined by the class

public class UserDefinedFieldForCsvMapper
{
    public int ColumnIndex { get; set; }

    public string FieldAlias { get; set; }

    public string FieldName { get; set; }
}

The FieldName property must match a property name on the class being used for representing the records being read or written. The property name can represent nested properties using a dot between properties (e.g. Product.Name a nested property of Transaction in the example provided).

[JoshClose]

Take a look at what AutoMap does.

CsvHelper/src/CsvHelper/Configuration/ClassMap.cs

Line 213 in eae9c4f

public virtual void AutoMap(CsvContext context)

Depending on what you need to do, it may be useful to just call AutoMap and then make changes from there.

Maybe I should add a method to map by a string like Map("A.B.C") and let CsvHelper do the work of setting it all up. I don't know how common of a thing when doing mapping on the fly it is to have the property tree in a string like that though.