c# - EF Core SQLITE - SQLite 错误 19 : 'UNIQUE constraint failed

Question

我正在学习 Entity Framework 核心，将其与 SQLITE 一起使用我在数据库中有 2 个表。

消息:

CREATE TABLE `Messages` (
    `Id`    INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT,
    `IsDeleted` INTEGER NOT NULL,
    `FromUserId`    INTEGER,
    `ToUserId`  INTEGER,
    `SendDate`  TEXT NOT NULL,
    `ReadDate`  TEXT NOT NULL,
    `MessageContent`    TEXT,
    CONSTRAINT `FK_Messages_Users_ToUserId` FOREIGN KEY(`ToUserId`) REFERENCES `Users`(`Id`) ON DELETE RESTRICT,
    CONSTRAINT `FK_Messages_Users_FromUserId` FOREIGN KEY(`FromUserId`) REFERENCES `Users`(`Id`) ON DELETE RESTRICT
);

和用户表:

CREATE TABLE `Users` (
    `Id`    INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT,
    `IsDeleted` INTEGER NOT NULL,
    `Name`  TEXT,
    `DisplayName`   TEXT,
    `Gender`    INTEGER NOT NULL,
    `BirthDate` TEXT NOT NULL
);

我的 C# 类看起来像:

public class User
{
    public int Id {get;set;}
    public bool IsDeleted{get;set;}
    [Required]
    public string Name{get;set;}

    public string DisplayName{get;set;}

    [Required]
    public char Gender{get;set;}

    [Required]
    public DateTime BirthDate{get;set;}

    public User(string n, string dn, char g, DateTime bd)
    {
        Name=n; DisplayName = dn; Gender = g; BirthDate = bd;
    }

    protected User(){}

    public override string ToString()
    {
        return string.Format("{0} ({1}) {2}", this.Name, this.Gender,this.BirthDate.ToShortDateString());
    }
}

和消息类:

public class Message 
{
    public int Id{get;set;}
    public bool IsDeleted{get;set;}
    [Required]
    public Users.User FromUser{get;set;}
    
    [Required]
    public Users.User ToUser{get;set;}

    [Required]
    public DateTime SendDate{get;set;}
    public DateTime? ReadDate{get;set;}

    [Required]
    public string MessageContent{get;set;}

    protected Message(){}

    public Message(User from, User to, string content)
    {
        this.FromUser = from;
        this.ToUser = to;
        this.MessageContent = content;
        this.SendDate = DateTime.Now;
        this.ReadDate = DateTime.Now;
    }

}

用户表有效，但是当我尝试通过此向消息添加新实体时:

public override int Insert(Message entity)
{
    dbc.Messages.Add(entity);
    dbc.SaveChanges();
    return entity.Id;
}

我收到以下错误:

SQLite Error 19: 'UNIQUE constraint failed

我不知道哪里出了问题。当我手动将数据插入数据库(使用 sqlite 的数据库浏览器)时，它起作用了。类(class)关系还好吗？

我的 dbContextSnapshot 是:

[DbContext(typeof(RandevouDbContext))]
partial class RandevouDbContextModelSnapshot : ModelSnapshot
{
    protected override void BuildModel(ModelBuilder modelBuilder)
    {
#pragma warning disable 612, 618
    modelBuilder.HasAnnotation("ProductVersion", "2.1.4-rtm-31024");

    modelBuilder.Entity("RandevouData.Messages.Message", b =>
        {
            b.Property<int>("Id")
                .ValueGeneratedOnAdd();

            b.Property<int>("FromUserId");

            b.Property<bool>("IsDeleted");

            b.Property<string>("MessageContent")
                .IsRequired();

            b.Property<DateTime?>("ReadDate");

            b.Property<DateTime>("SendDate");

            b.Property<int>("ToUserId");

            b.HasKey("Id");

            b.HasIndex("FromUserId");

            b.HasIndex("ToUserId");

            b.ToTable("Messages");
        });

    modelBuilder.Entity("RandevouData.Users.User", b =>
        {
            b.Property<int>("Id")
                .ValueGeneratedOnAdd();

            b.Property<DateTime>("BirthDate");

            b.Property<string>("DisplayName");

            b.Property<char>("Gender");

            b.Property<bool>("IsDeleted");

            b.Property<string>("Name")
                .IsRequired();

            b.HasKey("Id");

            b.ToTable("Users");
        });

    modelBuilder.Entity("RandevouData.Messages.Message", b =>
        {
            b.HasOne("RandevouData.Users.User", "FromUser")
                .WithMany()
                .HasForeignKey("FromUserId")
                .OnDelete(DeleteBehavior.Cascade);

            b.HasOne("RandevouData.Users.User", "ToUser")
                .WithMany()
                .HasForeignKey("ToUserId")
                .OnDelete(DeleteBehavior.Cascade);
        });
#pragma warning restore 612, 618
}

顺便说一下。我无法从两侧配置映射。

Message 实体有 UserFrom 和 UserTo 字段，但是用户实体不能有消息，因为一次他是“userFrom”而另一次他可以是“userTo”。

还有一个代码，我在其中创建消息实体

        public int SendMessage(int senderId, int receiverId, string content)
    {
        var dao = new MessagesDao();
        var usersDao = new UsersDao();
        var userService = new UserService(mapper);
        
        var sender = usersDao.Get(senderId);
        var receiver = usersDao.Get(receiverId);
        
        var entity = new Message(sender,receiver,content);
        var id = dao.Insert(entity);
        return id;
    }

我覆盖 GET 方法的用户 dao

 public override User Get(int id)
        {
            using (var context = new RandevouDbContext())
            { 
                var user = dbc.Find<User>(id);
                return user;
            }
        }

和我重写 Add 方法的 MessagesDao

 public override int Insert(Message entity)
        {
            using (var dc = new RandevouDbContext())
            {
                dc.Messages.Add(entity);
                dc.SaveChanges();
                return entity.Id;
            }
        }

顺便说一句，我不知道是否可以，但我有 0 个条目要更新(!？)

Answer 1

要修复“UNIQUE”约束异常，您需要确保您正在使用的所有实体都被您要保存到的上下文跟踪。

例如

// Get user from one context

User thisUser = db.Users.Find(3);

//Now imagine you have another context which has been created later on

DbContext newContext = new DbContext();

//and you want to create a message, assign it to your user 
//and save it to the new context

Message newMessage = new Message
{
    Text = "Hello",
    User = thisUser
}

newContext.Messages.Add(newMessage);

// saving this to newContext will fail because newContext is not tracking thisUser,
// Therefore attach it...

newContext.Users.Attach(thisUser).

//now newContext is tracking thisUser *AND* newMessage, so the save operation will work

newContext.SaveChanges();