Question

我有以下实体框架代码的第一个代码。创建表并插入数据。但是俱乐部表中有重复的记录。

我的运作是： -

使用分会创建应用创建分会
使用person app创建人员

如何避免重复录入？

enter image description here

    static void Main(string[] args)
    {
        Database.SetInitializer<NerdDinners>(new MyInitializer());

        CreateClubs();
        InsertPersons();

    }

    public static void CreateClubs()
    {

        string connectionstring = "Data Source=.;Initial Catalog=NerdDinners;Integrated Security=True;Connect Timeout=30";
        using (var db = new NerdDinners(connectionstring))
        {

            Club club1 = new Club();
            club1.ClubName = "club1";

            Club club2 = new Club();
            club2.ClubName = "club2";

            Club club3 = new Club();
            club3.ClubName = "club3";

            db.Clubs.Add(club1);
            db.Clubs.Add(club2);
            db.Clubs.Add(club3);

            int recordsAffected = db.SaveChanges();


        }
    }

    public static Club GetClubs(string clubName)
    {
        string connectionstring = "Data Source=.;Initial Catalog=NerdDinners;Integrated Security=True;Connect Timeout=30";
        using (var db = new NerdDinners(connectionstring))
        {

            //var query = db.Clubs.Where(p => p.ClubName == clubName);
            var query = db.Clubs.SingleOrDefault(p => p.ClubName == clubName);
            return query;
        }
    }

    public static void InsertPersons()
    {
        string connectionstring = "Data Source=.;Initial Catalog=NerdDinners;Integrated Security=True;Connect Timeout=30";
        using (var db = new NerdDinners(connectionstring))
        {

            Club club1 = GetClubs("club1");
            Club club2 = GetClubs("club2");
            Club club3 = GetClubs("club3");

            Person p1 = new Person();
            p1.PersonName = "Person1";

            Person p2 = new Person();
            p2.PersonName = "Person2";

            List<Club> clubsForPerson1 = new List<Club>();
            clubsForPerson1.Add(club1);
            clubsForPerson1.Add(club3);

            List<Club> clubsForPerson2 = new List<Club>();
            clubsForPerson2.Add(club2);
            clubsForPerson2.Add(club3);

            p1.Clubs = clubsForPerson1;
            p2.Clubs = clubsForPerson2;

            db.Persons.Add(p1);
            db.Persons.Add(p2);

            int recordsAffected = db.SaveChanges();


        }
    }

域

public class Person
{
    public int PersonId { get; set; }
    public string PersonName { get; set; }
    public virtual ICollection<Club> Clubs { get; set; }
}

public class Club
{
    public int ClubId { get; set; }
    public string ClubName { get; set; }
    public virtual ICollection<Person> Members { get; set; }
}

//System.Data.Entity.DbContext is from EntityFramework.dll
public class NerdDinners : System.Data.Entity.DbContext
{

    public NerdDinners(string connString): base(connString)
    { 

    }

    protected override void OnModelCreating(DbModelBuilder modelbuilder)
    {
         //Fluent API - Plural Removal
        modelbuilder.Conventions.Remove<PluralizingTableNameConvention>();
    }

    public DbSet<Person> Persons { get; set; }
    public DbSet<Club> Clubs { get; set; }

}

Answer 1

问题在于您创建了更多的上下文。

首先你创建了俱乐部。没关系。但是当你创建人员时，你会通过GetClubs获取俱乐部，但是对于每个俱乐部，你都会处理实际的实体框架上下文，这样你最终会得到分离的实体。在InsertPersons，您将新的俱乐部实体添加到新人中，因此实际情况会认为俱乐部是新的俱乐部。

因此，当您向某个人添加一个俱乐部时，您实际上会创建新的俱乐部。

这是因为实体框架跟踪变更并管理每个上下文的实体。如果您将实体添加到尚未包含它的上下文中，那么它将被视为一个新实体。

实际上，你应该做这样的事情（未经测试）：

static void Main(string[] args)
{
    Database.SetInitializer<NerdDinners>(new MyInitializer());

    string connectionstring = "Data Source=.;Initial Catalog=NerdDinners;Integrated Security=True;Connect Timeout=30";
    using (var db = new NerdDinners(connectionstring))
    {
        CreateClubs(db);
        InsertPersons(db);
    }

}

public static void CreateClubs(NerdDinners db)
{
    Club club1 = new Club();
    club1.ClubName = "club1";

    Club club2 = new Club();
    club2.ClubName = "club2";

    Club club3 = new Club();
    club3.ClubName = "club3";

    db.Clubs.Add(club1);
    db.Clubs.Add(club2);
    db.Clubs.Add(club3);

    int recordsAffected = db.SaveChanges();
}

public static Club GetClubs(string clubName, NerdDinners db)
{
    //var query = db.Clubs.Where(p => p.ClubName == clubName);
    var query = db.Clubs.SingleOrDefault(p => p.ClubName == clubName);
    return query;
}

public static void InsertPersons(NerdDinners db)
{
    Club club1 = GetClubs("club1", db);
    Club club2 = GetClubs("club2", db);
    Club club3 = GetClubs("club3", db);

    Person p1 = new Person();
    p1.PersonName = "Person1";

    Person p2 = new Person();
    p2.PersonName = "Person2";

    List<Club> clubsForPerson1 = new List<Club>();
    clubsForPerson1.Add(club1);
    clubsForPerson1.Add(club3);

    List<Club> clubsForPerson2 = new List<Club>();
    clubsForPerson2.Add(club2);
    clubsForPerson2.Add(club3);

    p1.Clubs = clubsForPerson1;
    p2.Clubs = clubsForPerson2;

    db.Persons.Add(p1);
    db.Persons.Add(p2);

    int recordsAffected = db.SaveChanges();
}

当然你应该重构这段代码的结构，但请注意我的操作只使用一个EF上下文。

Answer 2

感谢@PeterPorfy

另请阅读Exception of type 'System.ObjectDisposedException'

我用过

 ((IObjectContextAdapter)db).ObjectContext.Attach((IEntityWithKey)entity);

用于附加上一个上下文中的对象。

我使用的IEntityWithKey的一个例子如下。如果您发现此方法存在任何问题，请发表评论。

public class Person : IEntityWithKey
{
    public int PersonId { get; set; }
    public string PersonName { get; set; }

    public EntityKey EntityKey { get; set; }
}

请参阅以下内容

实体框架：多对多关系中的重复记录

2 个答案: