How to map database column to EF model property in a more efficient way than I'm doing now

Question

I have a nullable varchar(max) column in SQL Server that I'm mapping to a Guid? in EF code-first. However, this property is actually in a base class that many other entities derive from.

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Model1>().Property(e => e.Property1).HasConversion(p => p.ToString(), p => (Guid?)Guid.Parse(p));
}

The above line is repeated many times for each table. Is there a way to tell EF that this is a base class property so the mapping can be declared only once?

Answer 1

Sure it is possible. With the lack of custom conventions, it is achieved with the "typical" modelBuilder.Model.GetEntityTypes() loop. Something like this (just change the base class and the property names):

var entityTypes = modelBuilder.Model.GetEntityTypes()
    .Where(t => t.ClrType.IsSubclassOf(typeof(BaseClass)));

var valueConverter = new ValueConverter<Guid, string>(
    v => v.ToString(), v => (Guid?)Guid.Parse(v));

foreach (var entityType in entityTypes)
    entityType.FindProperty(nameof(BaseClass.Property1)).SetValueConverter(valueConverter);

You may also consider using the EF Core provided out of the box Guid to String converter:

var valueConverter = new GuidToStringConverter();

Answer 2

Better to make next calculation property:

[Column("Property1")]
public string Property1Raw { get; set; }

[IgnoreDataMember]
public Guid? Property1
{
    get => Guid.TryParse(Property1AsString, out Guid result) ? result : (Guid?)null;
    set => Property1Raw = value?.ToString();
}

Answer 3

Another way to do is it to have a matching base class IEntityTypeConfiguration:

internal class EntityConfiguration<T> : IEntityTypeConfiguration<T> where T : Entity
{
    public virtual void Configure(EntityTypeBuilder<T> builder)
    {
        builder.Property(e => e.Property1).HasConversion(p => p.ToString(), p => (Guid?)Guid.Parse(p));
        // ... Other base-specific config here
    }
}

(Assuming here your base class is called Entity - change as needed).

This works better when you use the pattern of factoring out your entity configurations, so yours might be like this:

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.ApplyConfiguration(new Model1EntityConfiguration());
    modelBuilder.ApplyConfiguration(new Model2EntityConfiguration());
    // ...
}

...

internal sealed class Model1EntityConfiguration : EntityConfiguration<Model1>
{
    public override void Configure(EntityTypeBuilder<Model1> builder)
    {
        base.Configure(builder); // <-- here's the key bit
        // ...; e.g.
        builder.Property(c => c.Name).HasMaxLength(80).IsRequired();
    }
}