XML columns in a Code-First application

Question

I'm trying to create an XML column in Code First. I'm well aware Entity Framework doesn't fully support XML columns, and that it reads them as a string. That's fine. I would still like the column type to be XML, though. Here's my class:

class Content
{
    public int ContentId { get; set; }

    [Column(TypeName="xml")]
    public string XmlString { get; set; }

    [NotMapped]
    public XElement Xml { get { ... } set { ... } }
 }

Problem is, that Code First Migrations completely ignores the Column attribute and creates the field as an nvarchar(max) . I tried using [DataType("xml")], but that, too, didn't work.

Is this a migration bug?

Answer 1

Have you tried:

public String XmlContent { get; set; }

public XElement XmlValueWrapper
{
    get { return XElement.Parse(XmlContent); }
    set { XmlContent = value.ToString(); }
}

public partial class XmlEntityMap : EntityTypeConfiguration<XmlEntity>
{
    public XmlEntityMap()
    {
        // ...
        this.Property(c => c.XmlContent).HasColumnType("xml");

        this.Ignore(c => c.XmlValueWrapper);
    }
}

Answer 2

I achieved what is needed with an attribute and I decorated my model class xml field with the attribute.

[XmlType]
public string XmlString { get; set; }

[NotMapped]
public XElement Xml
{
    get { return !string.IsNullOrWhiteSpace(XmlString) ? XElement.Parse(XmlString) : null; }
    set {
        XmlString = value == null ? null : value.ToString(SaveOptions.DisableFormatting);
    }
}

Got the help of these 2 articles:

https://entityframework.codeplex.com/wikipage?title=Code%20First%20Annotations

https://andy.mehalick.com/2014/02/06/ef6-adding-a-created-datetime-column-automatically-with-code-first-migrations/

Solution

Define Attribute

[AttributeUsage(AttributeTargets.Property, AllowMultiple = false)]
public class XmlType : Attribute
{
}

Register Attribute in Context

In the "OnModelCreating" of the context

modelBuilder.Conventions.Add(new AttributeToColumnAnnotationConvention<XmlType, string>("XmlType", (p, attributes) => "xml"));

Custom Sql Generator

public class CustomSqlGenerator : SqlServerMigrationSqlGenerator
{
    protected override void Generate(ColumnModel column, IndentedTextWriter writer)
    {
        SetColumnDataType(column);

        base.Generate(column, writer);
    }

    private static void SetColumnDataType(ColumnModel column)
    {
        // xml type
        if (column.Annotations.ContainsKey("XmlType"))
        {
            column.StoreType = "xml";
        }
    }
}

Register Custom Sql Generator

In the Migration Configuration constructor, register the custom SQL generator.

 SetSqlGenerator("System.Data.SqlClient", new CustomSqlGenerator());

Answer 3

But what if XmlContent is null ??

Maybe :

    public XElement XmlValueWrapper
    {
        get { return XmlContent != null ? XElement.Parse(XmlContent) : null; }
        set { XmlContent = value.ToString(); }
    }