FileHelpers动态固定字段位置

Question

Is it possible to parse/read a fixed position layout flat file when the positions are only known at run time? I see there is a question on SO that relates to something similar using 'Runtime Records' but this relates reading a delimited file - Dynamically create a Fixed Length text file with FileHelpers

My intention is to parse fixed length flat files with different fixed length formats to a common format, and the fixed length format is loaded at runtime. FileHelpers tends to use attributes to define the position and length of the field, which is defined up front but I would like to specify this at runtime.

thanks.

Answer 1

This is what i did. Hope it may help you.

1. Created DB table and stored the different Fixed File layout formats (like Field Name size, Data Type and Length of the field etc...)
2. In UI first user selects the Fixed File Layout and then selects the Fixed File to import.
3. Based on selected Layout i create Fixed length Type class at run time using the below code.

private void ImportFiles()
{
    DataTable dt = GetFixedFileSpecsFromDB(layoutName); //Get the specs
    //Create Dynamic class based on Specs above
    FixedLengthClassBuilder cb = GetSpecClass(dt);
    //Create FileHelpers engine instance
    FileHelperEngine engine = new FileHelperEngine(cb.CreateRecordClass());
    //Read file data into Data table
    DataTable dtImportData = engine.ReadFileAsDT(ImportFilePath);
}

//Method to create the Fixed lentgh dynamic class
 public static FixedLengthClassBuilder GetSpecClass(DataTable dt)
    {

        string className = "ImportSpecifications";
        FixedLengthClassBuilder cb = new FixedLengthClassBuilder(className);
        //Loop thru each field and prepare the class
        foreach (DataRow dr in dt.Rows)
        {
            int fieldLength = Convert.ToInt32(dr.Field<decimal>("FieldLength"));
            switch (dr["FieldDataType"].ToString())
            {
                case "String":
                    cb.AddField(dr.Field<string>("FieldName"), fieldLength, typeof(string));
                    cb.LastField.FieldNullValue = string.Empty;
                    cb.LastField.TrimMode = FileHelpers.TrimMode.Both;
                    break;
                case "Date":
                    cb.AddField(dr.Field<string>("FieldName"), fieldLength, typeof(DateTime));
                    cb.LastField.FieldNullValue = string.Empty;
                    break;
                case "Integer":
                    cb.AddField(dr.Field<string>("FieldName"), fieldLength, typeof(int?));
                    //cb.LastField.FieldNullValue = 0;
                    break;
                case "Long Integer":
                    cb.AddField(dr.Field<string>("FieldName"), fieldLength, typeof(long));
                    cb.LastField.FieldNullValue = 0;
                    break;
                case "Decimal":
                    cb.AddField(dr.Field<string>("FieldName"), fieldLength, typeof(decimal?));
                    //cb.LastField.FieldNullValue = 0;
                    break;
                default:
                    break;
            }
        }
        return cb;
    }