问题
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?
回答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 );
}
回答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;
}
回答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.
回答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;
}
来源：https://stackoverflow.com/questions/21257827/how-to-add-csvhelper-records-to-datatable-to-use-for-sqlbulkcopy-to-the-database