Início / coding / Perguntas / 79565921
Accepted
Ivan Debono
Asked: 2025-04-10 14:54:22 +0800 CST

Como usar conversão de tipos no Entity Framework Core?

  • 772

Eu tenho esta entidade:

public class Customer
{
    public int Id { get; set; }
    public string Email { get; set; }
    public IEnumerable<Order> Orders{ get; set; } = [];
    internal byte[] OrdersArray { get; set; }

    public User()
    { }
}

E o mapeamento:

internal class CustomerMap : EntityMappingConfiguration<Customer>
{
    public override void Map(EntityTypeBuilder<Customer> b)
    {
        b.ToTable("Customers").HasKey(t => t.Id);
        b.Property(t => t.Id).HasColumnName("Id").ValueGeneratedOnAdd();
        b.Property(t => t.Email).HasColumnName("Email").IsRequired();
        b.Property(t => t.OrdersArray).HasColumnName("Orders");
        b.Ignore(t => t.Orders);
    }
}

Como posso usar a conversão EFCore para converter a matriz de bytes para a lista e vice-versa na leitura/gravação automaticamente?

c#

1 respostas

  1. Best Answer
    using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Metadata.Builders;
using Microsoft.EntityFrameworkCore.ChangeTracking; // required for valuecomparer
using Microsoft.EntityFrameworkCore.Storage.ValueConversion;
using System.Text.Json;
using System.Collections.Generic;
using System.Linq; // for sequenceequal and aggregate

// 1. define your order class (must be serializable)
public class Order
{
    public int OrderId { get; set; }
    // ... other properties
    // optional: implement equals/gethashcode for comparer
    public override bool Equals(object obj) => obj is Order o && OrderId == o.OrderId;
    public override int GetHashCode() => OrderId.GetHashCode();
}

// 2. update your customer entity
public class Customer
{
    public int Id { get; set; }
    public string Email { get; set; }
    // use this property directly
    public IEnumerable<Order> Orders { get; set; } = new List<Order>();

    // no byte[] property needed here when using conversion
    public Customer() { }
}

// 3. configure the mapping with hasconversion
internal class CustomerMap : IEntityTypeConfiguration<Customer>
{
    public void Configure(EntityTypeBuilder<Customer> b)
    {
        b.ToTable("Customers").HasKey(t => t.Id);
        b.Property(t => t.Id).ValueGeneratedOnAdd();
        b.Property(t => t.Email).IsRequired();

        // configure conversion for the orders property
        b.Property(t => t.Orders)
            .HasColumnName("OrdersData") // *** use your actual db column name for the byte[] ***
            .HasConversion(
                // convert IEnumerable<Order> to byte[] for db storage
                v => JsonSerializer.SerializeToUtf8Bytes(v, (JsonSerializerOptions)null),
                // convert byte[] from db back to List<Order>
                v => (v == null || v.Length == 0)
                     ? new List<Order>() // handle null/empty data
                     : JsonSerializer.Deserialize<List<Order>>(v, (JsonSerializerOptions)null) ?? new List<Order>()
            )
            // add a value comparer for ef core change tracking of collections
            .Metadata.SetValueComparer(new ValueComparer<IEnumerable<Order>>(
                (c1, c2) => (c1 == null && c2 == null) || (c1 != null && c2 != null && c1.SequenceEqual(c2)),
                c => c == null ? 0 : c.Aggregate(0, (a, v) => HashCode.Combine(a, v.GetHashCode())),
                c => c == null ? new List<Order>() : c.ToList() // snapshotting
            ));
    }
}
    • 0

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