By default convention, strings properties in an entity model that are not explicitly given a max length are set to nvarchar(max)
in the database. We wish to override this convention and give strings a max length of nvarchar(100)
if they are not already explicitly set otherwise.
I discovered the PropertyMaxLengthConvention
built-in convention, which by its description and documentation would seem to be what I am looking for. However, it either doesn't work or I'm using it wrong or it just doesn't do what I think it does.
I've tried simply adding the convention:
modelBuilder.Conventions.Add(new PropertyMaxLengthConvention(100));
Then I thought maybe the default one is already being used, so I tried removing it first:
modelBuilder.Conventions.Remove<PropertyMaxLengthConvention>();
modelBuilder.Conventions.Add(new PropertyMaxLengthConvention(100));
I even tried explictly adding the convention before and after the default one:
modelBuilder.Conventions.AddBefore<PropertyMaxLengthConvention>(new PropertyMaxLengthConvention(100));
modelBuilder.Conventions.AddAfter<PropertyMaxLengthConvention>(new PropertyMaxLengthConvention(100));
No joy. When I add migrations, the columns are still created as nvarchar(max)
.
Is there a way to use that convention to do what I want? If not, can I write a custom convention that will default string properties to nvarchar(100)
but will still allow me to explicitly set them to a different value including maxlength?
After tracking down the source code for the aforementioned convention, I discovered that it only sets the default max length for properties that are specified to have fixed length. (Bizarre!)
So I took the source code and modified it to create my own convention. Now string properties with unspecified max length will have a default max length instead of being nvarchar(max). The only downside is there doesn't appear to be a way to detect when the IsMaxLength()
configuration is explicitly applied. So if I have a column that I do want to have created as nvarchar(max) I can't use IsMaxLength()
to do it.
To address this, I created an extension method for StringPropertyConfiguration called ForceMaxLength()
that configures the property with HasMaxLength(int.MaxValue)
- ordinarily an invalid value, but one for which I can easily test in my custom convention. When I detect it, I simply set the MaxLength back to null and set the IsMaxLength to true and let the property configuration continue as normal.
Here's the custom convention:
using System;
using System.Collections.Generic;
using System.Data.Entity.Core.Metadata.Edm;
using System.Data.Entity.Infrastructure;
using System.Data.Entity.ModelConfiguration.Conventions;
namespace MyProject.CustomConventions
{
public class CustomPropertyMaxLengthConvention : IConceptualModelConvention<EntityType>, IConceptualModelConvention<ComplexType>
{
private const int DefaultLength = 128;
private readonly int length;
public CustomPropertyMaxLengthConvention()
: this(DefaultLength)
{
}
public CustomPropertyMaxLengthConvention(int length)
{
if (length <= 0)
{
throw new ArgumentOutOfRangeException("length", "Invalid Max Length Size");
}
this.length = length;
}
public virtual void Apply(EntityType item, DbModel model)
{
SetLength(item.DeclaredProperties);
}
public virtual void Apply(ComplexType item, DbModel model)
{
SetLength(item.Properties);
}
private void SetLength(IEnumerable<EdmProperty> properties)
{
foreach (EdmProperty current in properties)
{
if (current.IsPrimitiveType)
{
if (current.PrimitiveType == PrimitiveType.GetEdmPrimitiveType(PrimitiveTypeKind.String))
{
SetStringDefaults(current);
}
if (current.PrimitiveType == PrimitiveType.GetEdmPrimitiveType(PrimitiveTypeKind.Binary))
{
SetBinaryDefaults(current);
}
}
}
}
private void SetStringDefaults(EdmProperty property)
{
if (property.IsUnicode == null)
{
property.IsUnicode = true;
}
SetBinaryDefaults(property);
}
private void SetBinaryDefaults(EdmProperty property)
{
if (property.MaxLength == int.MaxValue)
{
property.MaxLength = null;
property.IsMaxLength = true;
}
else if (property.MaxLength == null || !property.IsMaxLength)
{
property.MaxLength = length;
}
}
}
}
Here's the extension method:
using System.Data.Entity.ModelConfiguration.Configuration;
namespace MyProject.Model.Mapping
{
public static class MappingExtensions
{
public static void ForceMaxLength(this StringPropertyConfiguration obj)
{
obj.HasMaxLength(int.MaxValue);
}
}
}
Here's how it's used:
using System.Data.Entity.ModelConfiguration;
namespace MyProject.Model.Mapping
{
public class MyEntityMap : EntityTypeConfiguration<MyEntity>
{
public MyEntityMap()
{
Property(v => v.StringValue).ForceMaxLength();
}
}
}