EF 4.1 Code First – 在使用新的上下文/通过WCF时更改为未更新的FK值

2019年8月3日 240次阅读

我在WCF上使用EF Code First.因此,当我保存实体时,它正在使用新的上下文.

如果我检索一个实体,然后更新它以便它引用一个不同的实体,我发现它保存了原始的外键值.

例如,我检索公司类,其中国家是英国.然后我将其更改为USA并将其传递回服务.当我检查表时,FK仍然设置为英国.

如何更新外键？

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data.Entity.ModelConfiguration;
using System.ComponentModel.DataAnnotations;
using System.Data.Entity;
using System.Data;

namespace CodeFirstExistingDatabase
{

    class Program
    {
        private const string ConnectionString = @"Server=.\sql2005;Database=CodeFirst2;integrated security=SSPI;";

        static void Main(string[] args)
        {

            // Firstly, create a new country record.
            Country country = new Country();
            country.Code = "UK";
            country.Name = "United Kingdom";

            // Create aother new country record.
            Country country2 = new Country();
            country2.Code = "USA";
            country2.Name = "US of A";

            // Now create an instance of the context.
            MyContext myContext = new MyContext(ConnectionString);
            myContext.Entry(country).State = EntityState.Added;
            myContext.Entry(country2).State = EntityState.Added;
            myContext.SaveChanges();
            Console.WriteLine("Saved Countries");

            // Now insert a Company record
            Company company = new Company();
            company.CompanyName = "AccessUK";
            company.HomeCountry = myContext.Countries.First(e => e.Code == "UK");
            myContext.Companies.Add(company);
            myContext.SaveChanges();
            Console.WriteLine("Saved Company");

            Company savedCompany = myContext.Companies.First(e => e.CompanyName == "AccessUK");
            Country usCountry = myContext.Countries.First(e => e.Code == "USA");
            savedCompany.HomeCountry = usCountry;

            // Create another context for the save (as if we're passing the entity back over WCF and thus
            // creating a new context in the service)
            MyContext myContext2 = new MyContext(ConnectionString);
            myContext2.Entry(savedCompany).State = EntityState.Modified;
            myContext2.Entry(savedCompany.HomeCountry).State = EntityState.Modified;
            myContext2.SaveChanges();

            // When I check the company table, it has the foreign key of the UK Country.  It should have 
            // that of USA.

            Console.WriteLine("Finished");
            Console.ReadLine();

        }
    }

        public class MyContext
            : DbContext
        {
            public DbSet<Company> Companies { get; set; }
            public DbSet<Country> Countries { get; set; }

            public MyContext(string connectionString)
                : base(connectionString)
            {
            }
            protected override void OnModelCreating(DbModelBuilder modelBuilder)
            {
                modelBuilder.Configurations.Add(new CountryConfiguration());
                modelBuilder.Configurations.Add(new CompanyConfiguration());

                base.OnModelCreating(modelBuilder);
            }
        }

    public class CompanyConfiguration
        : EntityTypeConfiguration<Company>
    {

        public CompanyConfiguration()
            : base()
        {

            HasKey(p => p.Id);
            Property(p => p.Id)
                .HasColumnName("Id")
                .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity)
                .IsRequired();

            Property(p => p.CompanyName)
                .HasColumnName("Name")
                .IsRequired();
            HasRequired(x => x.HomeCountry).WithMany()
                .Map(x => x.MapKey("HomeCountryId"));

            ToTable("Companies");
        }

    }

    public class CountryConfiguration
        : EntityTypeConfiguration<Country>
    {

        /// <summary>
        /// Initializes a new instance of the <see cref="CountryConfiguration"/> class.
        /// </summary>
        public CountryConfiguration()
            : base()
        {

            HasKey(p => p.Id);
            Property(p => p.Id)
                .HasColumnName("Id")
                .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity)
                .IsRequired();
            Property(p => p.Code)
                .HasColumnName("Code")
                .IsRequired();
            Property(p => p.Name)
                .HasColumnName("Name")
                .IsRequired();

            ToTable("Countries");
        }

    }

    public class Company
    {
        public int Id { get; set; }
        public string CompanyName { get; set; }
        public Country HomeCountry { get; set; }
    }

    public class Country
    {
        public int Id { get; set; }
        public string Code { get; set; }
        public string Name { get; set; }
    }
}

非常感谢,

保罗.

最佳答案 这是分离实体和独立关联的众所周知的问题.问题是将实体设置为已修改不会将关系设置为已修改.关于所有相关问题的详细描述
is here.答案与EFv4和ObjectContext API有关,但EFv4.1只是它的包装,因此含义相同.

此问题的根源是,如果您使用分离的实体,则必须说EF关系已更改. EF不会为您做任何假设. DbContext API的问题更糟糕,因为DbContext API doesn’t offer methods to change state of independent association所以你必须恢复到ObjectContext API并使用ObjectStateManager.ChangeRelationshipState.

如果您不使用远程调用作为WCF,还有其他方法可以处理它 – 它只是为了使其工作必须执行的命令顺序,但在使用WCF时,您无法在设置关系之前附加实体等理论上你可以,但它会完全改变你的服务合同和消息编排.

因此,在这种情况下,通常最简单的解决方案是使用foreign key association instead of independent association.外键关联不会被跟踪为具有状态的独立对象(作为独立关联),因此将实体的状态更改为已修改将正常工作.

public class Company
{
    public int Id { get; set; }
    public string CompanyName { get; set; }
    public int HomeCountryId { get; set; }
    public Country HomeCountry { get; set; }
}


HasRequired(x => x.HomeCountry)
    .WithMany()
    .HasForeignKey(x => x.HomeCountryId);

任何其他解决方案是关于首先从DB加载旧对象并将更改合并到附加对象 – 这就是我一直在做的事情,一旦你开始处理多对多关系或删除一个关系,你将不得不这样做多对多的关系.

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