EntityFramework Core 与组合键的关系

使用EntityFramework Core处理具有组合键的数据是一个常见的需求。组合键是由多个列组成的主键，用于唯一标识数据表中的每一行。在EntityFramework Core中，可以使用Fluent API或数据注释来定义组合键。本文将介绍如何使用EntityFramework Core与组合键进行数据操作，并提供一个相关的案例代码。

csharp
public class MyDbContext : DbContext
{
    public DbSet MyEntities { get; set; }
    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity()
            .HasKey(e => new { e.Column1, e.Column2 });
        modelBuilder.Entity()
            .HasIndex(e => new { e.Column1, e.Column2 });
    }
}
public class MyEntity
{
    public int Column1 { get; set; }
    public int Column2 { get; set; }
    public string Data { get; set; }
}

csharp
using (var context = new MyDbContext())
{
    var entities = context.MyEntities
        .Where(e => e.Column1 == 1 && e.Column2 == 2)
        .ToList();
}

csharp
using (var context = new MyDbContext())
{
    var entity = new MyEntity
    {
        Column1 = 1,
        Column2 = 2,
        Data = "Some data"
    };
    context.MyEntities.Add(entity);
    context.SaveChanges();
}

csharp
using (var context = new MyDbContext())
{
    var entity = context.MyEntities
        .FirstOrDefault(e => e.Column1 == 1 && e.Column2 == 2);
    if (entity != null)
    {
        entity.Data = "Updated data";
        context.SaveChanges();
    }
}

csharp
using (var context = new MyDbContext())
{
    var entity = context.MyEntities
        .FirstOrDefault(e => e.Column1 == 1 && e.Column2 == 2);
    if (entity != null)
    {
        context.MyEntities.Remove(entity);
        context.SaveChanges();
    }
}