This StackOverflow question points out an issue with EntityFramework 4.1, when used with a SQL Server Compact table with image columns. The “image” type is the predecessor to varbinary(MAX), and is used for storing large binary values, sometimes referred to as BLOBs.
I have created a sample Console application with fixes for the related issues.
To re-create the application, install EntityFramwork 4.1, create a C# Windows Console application in Visual Studio 2010, and add .NET references to:
System.Data.Entity
EntityFramework
System.ComponentModel.DataAnnotations
Then add code similar to this:
using System;
using System.ComponentModel.DataAnnotations;
using System.Data.Entity;
//Also added reference to EntityFramework.dll (EF 4.1)
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;
namespace CfTest
{
class Program
{
static void Main(string[] args)
{
using (var db = new StudentContext())
{
var student = new Student { Name = "Erik", Photo = ConvertImageToByteArray(@"C:\Users\Erik\Pictures\erik.jpg"), StudentId = 1 };
student.LongText = new string('x', 6666);
db.Students.Add(student);
int recordsAffected = db.SaveChanges();
Console.WriteLine(
"Saved {0} entities to the database, press any key to exit.",
recordsAffected);
Console.ReadKey();
}
}
private static byte[] ConvertImageToByteArray(string fileName)
{
Bitmap bitMap = new Bitmap(fileName);
ImageFormat bmpFormat = bitMap.RawFormat;
var imageToConvert = Image.FromFile(fileName);
using (MemoryStream ms = new MemoryStream())
{
imageToConvert.Save(ms, bmpFormat);
return ms.ToArray();
}
}
}
public class Student
{
public int StudentId { get; set; }
public string Name { get; set; }
// Required to force Code First to create a ntext column, not a nvarchar(n)
[Column(TypeName = "ntext")]
public string LongText { get; set; }
// Required to force Code First to create an image column, not a binary(n)
[Column(TypeName = "image")]
public byte[] Photo { get; set; }
}
public class StudentContext : DbContext
{
protected override bool ShouldValidateEntity(System.Data.Entity.Infrastructure.DbEntityEntry entityEntry)
{
// Required to prevent bug - http://stackoverflow.com/questions/5737733
if (entityEntry.Entity is Student)
{
return false;
}
return base.ShouldValidateEntity(entityEntry);
}
public DbSet<Student> Students { get; set; }
}
}
And add an app.config with contents like this. The connection string name matches the DbContext name and this causes Code First to magically create a database file in the specified location, with a Students table:
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<connectionStrings>
<add name="StudentContext"
providerName="System.Data.SqlServerCe.4.0"
connectionString="Data Source=C:\Users\Erik\Documents\visual studio 2010\Projects\CfTest\Students.sdf"/>
</connectionStrings>
</configuration>
This is the resulting Students table:
-- Script Date: 11-07-2011 09:43 - Generated by ExportSqlCe version 3.5.1.3
CREATE TABLE [Students] (
[StudentId] int NOT NULL IDENTITY (1,1)
, [Name] nvarchar(4000) NULL
, [LongText] ntext NULL
, [Photo] image NULL
);
GO
ALTER TABLE [Students] ADD CONSTRAINT [PK__Students__000000000000000A] PRIMARY KEY ([StudentId]);
GO
This code demonstrates how to convert an image to a byte array, and also highlights the fixes required to work with image columns:
// Required to force Code First to create an image column, not a binary(n)
[Column(TypeName = "image")]
public byte[] Photo { get; set; }
The Photo column must be decorated with the Column attribute specifying a typeName of “Image.
// Required to force Code First to create a ntext column, not a nvarchar(n)
[Column(TypeName = "ntext")]
public string LongText { get; set; }
Likewise the LongText column must specify “ntext” as typename.
public class StudentContext : DbContext
{
protected override bool ShouldValidateEntity(System.Data.Entity.Infrastructure.DbEntityEntry entityEntry)
{
// Required to prevent bug - http://stackoverflow.com/questions/5737733
if (entityEntry.Entity is Student)
{
return false;
}
return base.ShouldValidateEntity(entityEntry);
}
public DbSet<Student> Students { get; set; }
}
And validation must be disabled to prevent an error message saying:
Validation failed for one or more entities. See 'EntityValidationErrors' property for more details. This issue is described by the ADO.NET Team here.
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