How to add CsvHelper records to DataTable to use for SqlBulkCopy to the database

Question

I am trying to read a CSV file with CsvHelper, load each record into a DataTable, and then use SqlBulkCopy to insert the data into a database table. With the current code, I get an exception when adding a row to the DataTable. The exception is: "Unable to cast object of type 'MvcStockAnalysis.Models.StockPrice' to type 'System.IConvertible'.Couldn't store in Date Column. Expected type is DateTime."

The example CSV file is from yahoo finance. For example: http://ichart.yahoo.com/table.csv?s=MMM&a=0&b=1&c=2010&d=0&e=17&f=2014&g=d&ignore=.csv

The CSV file contains the following header: Date Open High Low Close Volume Adj Close

The model that I am reading the CSV file into:

namespace MvcStockAnalysis.Models
{
    using System;
    using System.Collections.Generic;

    public partial class StockPrice
    {
        public int Id { get; set; }
        public System.DateTime Date { get; set; }
        public int CompanyId { get; set; }
        public double High { get; set; }
        public double Low { get; set; }
        public double Close { get; set; }
        public double AdjClose { get; set; }
        public double Open { get; set; }
        public double Volume { get; set; }

        public virtual Company Company { get; set; }
    }
}

The mapping of the CSV file to the StockPrice class uses the following:

public class StockPriceClassMap : CsvClassMap<StockPrice>
{
    public override void CreateMap()
    {
        Map(m => m.Date).Name("Date");
        Map(m => m.Close).Name("Close");
        Map(m => m.AdjClose).Name("Adj Close");
        Map(m => m.High).Name("High");
        Map(m => m.Low).Name("Low");
        Map(m => m.Open).Name("Open");
        Map(m => m.Volume).Name("Volume");
    }
}

The code that tries to add the CsvHelper records to the DataTable is as follows:

var connectionstring = ConfigurationManager.ConnectionStrings["MvcStockAnalysis.Models.MvcStockAnalysisContext"];
var connection = new SqlConnection();
connection.ConnectionString = connectionstring.ToString();
var destinationTableName = "StockPrices";
var company = db.Company
            .Where(c => c.Symbol == "MMM")
            .FirstOrDefault();

try
{
    string path = HttpContext.Server.MapPath("~/App_Data/" + company.Symbol + @".csv");

    if (System.IO.File.Exists(path))
    {     

        using (StreamReader sr = new StreamReader(path))
        {
            using (var csv = new CsvReader(sr))
            {
                DataTable dt = new DataTable("StockPrices");
                csv.Configuration.HasHeaderRecord = true;
                csv.Configuration.RegisterClassMap<StockPriceClassMap>();

                dt.Columns.Add(new DataColumn("Date", typeof(DateTime)));
                dt.Columns.Add(new DataColumn("Close", typeof(Double)));
                dt.Columns.Add(new DataColumn("AdjClose", typeof(Double)));
                dt.Columns.Add(new DataColumn("High", typeof(Double)));
                dt.Columns.Add(new DataColumn("Low", typeof(Double)));
                dt.Columns.Add(new DataColumn("Open", typeof(Double)));
                dt.Columns.Add(new DataColumn("Volume", typeof(Double)));
                dt.Columns.Add(new DataColumn("CompanyId", typeof(Double)));
                var records = csv.GetRecords<StockPrice>().ToList();
                foreach (var record in records)
                {                                    
                    record.CompanyId = company.Id;
                    dt.Rows.Add(record);
                }
                // add dt to the database
                using (var bulkCopy = new SqlBulkCopy(connection.ConnectionString))
                {
                    // DataTable column names match my SQL Column names, so I simply made this loop. 
                    foreach (DataColumn col in dt.Columns)
                    {
                        bulkCopy.ColumnMappings.Add(col.ColumnName, col.ColumnName);
                    }
                    bulkCopy.DestinationTableName = destinationTableName;
                    bulkCopy.WriteToServer(dt);
                }
            }
        }
    }
    connection.Close();
}
catch (Exception e)
{
    Console.Write(e.Message);
}

How can I add CsvHelper records to DataTable to use for SqlBulkCopy to the database?

Answer 1

If I'm not mistaken, you should be able to do it with a lot less code. You don't have to put in into another class before going into the DataTable either.

while( csv.Read() )
{
    var row = dt.NewRow();
    foreach( DataColumn column in dt.Columns )
    {
        row[column.ColumnName] = csv.GetField( column.DataType, column.ColumnName );
    }
    dt.Rows.Add( row );
}

Answer 2

Josh added support to read headers last year and the following block may be useful to those who just want to build a DataTable using the schema of the CSV document. I wanted to post this as a comment to Josh's answer as it is only a small modification but posting as an answer as I couldn't format a code block in Comments.

    private DataTable BuildDataTable()
    {
        var dt = new DataTable();

        using (var textReader = new StreamReader(_path))
        {
            using (var csv = new CsvReader(textReader))
            {
                csv.ReadHeader();
                foreach (var header in csv.FieldHeaders)
                {
                    dt.Columns.Add(header);
                }


                while (csv.Read())
                {
                    var row = dt.NewRow();
                    foreach (DataColumn column in dt.Columns)
                    {
                        row[column.ColumnName] = csv.GetField(column.DataType, column.ColumnName);
                    }
                    dt.Rows.Add(row);
                }
            }
        }

        return dt;
    }

Answer 3

I was able to get this to work by adding a DataTable row and filling it in explicitly, instead of trying to add a CsvHelper record as a row.

I used the following part instead of the similar part that is shown above:

foreach (var record in records)
{
    DataRow row = dt.NewRow();
    record.CompanyId = company.Id;
    row["Date"] = record.Date;
    row["Close"] = record.Close;
    row["AdjClose"] = record.AdjClose;
    row["High"] = record.High;
    row["Low"] = record.Low;
    row["Open"] = record.Open;
    row["Volume"] = record.Volume;
    row["CompanyId"] = record.CompanyId;
    dt.Rows.Add(row);
}

If you can solve the issue without so much hard coding, I will accept your answer as the answer.

Answer 4

I liked the answer from @JoshClose, but I found while( csv.Read() ) to be considerably slower than csv.GetRecords<{Class}>().ToList(). It also doesn't correctly handle many nullable types like int? when the value returned should be DBNull. My answer is to have CsvHelper import a list of dynamic records and then use a couple helper methods to auto map to the DataTable.

var records = csv.GetRecords<dynamic>().ToList();

foreach ( record in records )
{
    var row = dt.NewRow();

    var recordDictionary = DynamicToDictionary( record );

    foreach( DataColumn column in dt.Columns )
    {
        row[column.ColumnName] = GetColumnValue( column, recordDictionary );
    }

    dt.Rows.Add( row );
}

The DynamicToDictionary method handles case sensitivity and header white space. I convert the dynamic object to a Dictionary object that ignores case sensitivity and removes header white space. This could be skipped and the dynamic object passed directly to GetColumnValue if this isn't an issue.

public Dictionary<string, object> DynamicToDictionary(dynamic dynObj)
{
    var dictionary = new Dictionary<string, object>(StringComparer.OrdinalIgnoreCase);

    foreach (var kvp in (IDictionary<string, object>) dynObj)
    {
        var obj = kvp.Value;

        // Remove white space.
        var name = new string(kvp.Key.ToCharArray().Where(c => !char.IsWhiteSpace(c)).ToArray());

        dictionary.Add(name, obj);
    }

    return dictionary;
}

The GetColumnValue method finds and converts the dynamic record value into the proper DataTable column value.

public object GetColumnValue(DataColumn column, IDictionary<string, object> dynamicDictionary)
{
    object value;

    // Return DBNull if the column name isn't found.
    if (!dynamicDictionary.TryGetValue(column.ColumnName, out value))
    {
        return DBNull.Value;
    }

    // Null values come in as empty strings.
    if (column.AllowDBNull && column.DataType != typeof(string) && (string)value == "")
    {
        return DBNull.Value;
    }

    if (column.DataType == typeof(bool))
    {
        return (string)value != "0" && ((string)value).ToLower() != "false";
    }

    return value;
}