在 EF Core 中使用不同的名称指定关系

Question

I have a problem with the following relationship in EF Core 3.1.8. I have the following classes:

public class UnitOfMeasure
{
    public UnitOfMeasure(string Code, string Description)
    {
        this.Code = Code;
        this.Description = Description;
    }
    public int Id { get; private set; }
    public string Code { get; private set; }
    public string Description { get; private set; }
}

public class Article
{
    private Article() { }
    public Article(string Code, string Description, UnitOfMeasure BaseUnitOfMeasure)
    {
        this.Code = Code;
        this.Description = Description;
        this.BaseUnitOfMeasure = BaseUnitOfMeasure;
        this.BaseUnitOfMeasureId = BaseUnitOfMeasure.Id;
    }
    public int Id { get; private set; }
    public string Code { get; private set; }
    public string Description { get; private set; }
    public int BaseUnitOfMeasureId { get; private set; }
    public UnitOfMeasure BaseUnitOfMeasure { get; private set; }
}

internal class ArticleConfiguration : IEntityTypeConfiguration<Article>
{
    public void Configure(EntityTypeBuilder<Article> builder)
    {
        builder.HasIndex(a => a.Code)
            .IsUnique();

        builder.HasOne(a => a.BaseUnitOfMeasure)
            .WithMany()
            .HasForeignKey(a => a.BaseUnitOfMeasureId)
            .OnDelete(DeleteBehavior.Restrict);
    }
}

public class WmsDbContext : DbContext
{
    public WmsDbContext(DbContextOptions options)
        : base(options)
    {
        ChangeTracker.LazyLoadingEnabled = false;
    }

    protected override void OnModelCreating(ModelBuilder builder)
    {
        foreach (var assembly in AppDomain.CurrentDomain.GetAssemblies())
        {
            builder.ApplyConfigurationsFromAssembly(assembly);
        }

        base.OnModelCreating(builder);
    }
}

... When I run this, I'm getting the following error: : 'Unable to determine the relationship represented by navigation property 'Article.BaseUnitOfMeasure' of type 'UnitOfMeasure'. Either manually configure the relationship, or ignore this property using the '[NotMapped]' attribute or by using 'EntityTypeBuilder.Ignore' in 'OnModelCreating'.'

This is driving me mad. I can't find anything to get a relationship to work. I don't want to specify the other side of the relation on the UnitOfMeasure class, because this makes no sense in my domain.

How can I add a navigation property with a different name than the class?

Answer 1

Your relationship is one UnitOfMeasure with many Articles, right? If so you can simply add the following code to the UnitOfMeasure class:

public ICollection<Article> Articles { get; set; }

and change the builder.HasOne like this:

builder.HasOne(d => d.BaseUnitOfMeasure)
       .WithMany(p => p.Articles)
       .HasForeignKey(d => d.BaseUnitOfMeasureId)
       .OnDelete(DeleteBehavior.Restrict)
       .HasConstraintName("FK_Articles_BaseUnitOfMeasure");

Actually adding a collection of Articles to the unitOfMeasure class is enough and you no longer need to add builder.HasOne, unless you want a specific delete behavior.

By the way, C# 9.0 introduces record types, which are a reference type that provides synthesized methods to provide value semantics for equality. Records are immutable by default. So you no longer need to have a private setter in your class.

Answer 2

Problem solved. I had no key in the UnitOfMeasure class. After adding the Id everything worked as expected.