Array of string is null ASP.NET Core Entity Framework

Question

Array of string is null ASP.NET Core Entity Framework

asp.net-core entity-framework-core

Question

I have a classes which are represented as below:

public abstract class TankModel
{
    protected static readonly char delimiter = ',';

    protected string _destinations = "";

    [Key]
    public int ID { get; set; }
    [NotMapped]
    public String[] Destinations
    {
        get
        {
            return _destinations.Split(delimiter);
        }
        set
        {
            _destinations = String.Join($"{delimiter}", value);
        }
[..........................]
    }
}

public class NormalTank : TankModel
{
    public double VolumeTotal { get; set; }
[.........]
}

My OnModelCreating method contains:

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.Entity<TankModel>().Property<string>("Outputs").HasField("_destinations");
            modelBuilder.Entity<TankModel>().ToTable("Tanks");
            modelBuilder.Ignore<TankModel>();
            modelBuilder.Entity<NormalTank>().HasBaseType<TankModel>();
[..................]
        }

When I'm displaying NormalTank rows, Destinations columns is empty.

I'm trying to display data without inheriting, then Destinations column has the right value. I suspect that modelBuilder.Ignore<TankModel>(); causes this problem, but without this property I don't build a migration.

I'm fighting with this problem since few hours and I don't see any solutions.

How can I save Destinations in my database?

Lutz Harrold

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Chris Pickford · Accepted Answer · 10/8/2018 1:19:46 PM

Provided you are using EF Core 2.1 or greater, you can leverage a custom ValueConverter.

E.g. for the following class:

public class Example
{
  public Example() { Values = new List<string>(); }
  public ICollection<string> Values { get; set; }
}

You can simply configure a converter in your DbContext:

modelBuilder.Entity<Example>(b => b.Property(x => x.Values)
  .HasConversion(new StringCollectionToStringConverter()));

Having created a converter class as follows:

public class StringCollectionToStringConverter : ValueConverter<ICollection<string>, string>
{
  private static readonly Expression<Func<string, ICollection<string>>> ToListValue
    = str => str.Split('|', StringSplitOptions.RemoveEmptyEntries);

  private static readonly Expression<Func<ICollection<string>, string>> ToStringValue
    = list => string.Join('|', list);

  public StringCollectionToStringConverter(ConverterMappingHints mappingHints = null)
    : base(ToStringValue, ToListValue, mappingHints) { }

  public static ValueConverterInfo DefaultInfo
    => new ValueConverterInfo(typeof(ICollection<string>), typeof(string),
      i => new StringCollectionToStringConverter(i.MappingHints));
}

Array of string is null ASP.NET Core Entity Framework

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