Entity Framework 可以查询数据但不能保存

Question

我正在使用 EF5，并且我有一些我自己编写的实体，还编写了一个将所有映射添加到模型构建器配置的函数。

运行一个简单的测试查询，我可以成功地从表中查询项目，但是当我尝试添加一个新项目并保存时，我得到一个异常，即我的实体的主键为空，即使我给它一个值.

很可能是我搞砸了映射，但我不知道为什么它适用于查询而不是保存。

public class User : IMappedEntity 
{
    [Key]
    [Column("USER_ID")]
    public int UserID { get; set; }

    [Column("FIRST_NAME")]
    public String FirstName { get; set; }

    [Column("LAST_NAME")]
    public String LastName { get; set; }

}

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
        modelBuilder.Conventions.Remove<System.Data.Entity.ModelConfiguration.Conventions.PluralizingEntitySetNameConvention>();
        modelBuilder.Conventions.Remove<System.Data.Entity.ModelConfiguration.Conventions.PluralizingTableNameConvention>();

    var addMethod = (from m in (modelBuilder.Configurations).GetType().GetMethods()
                     where m.Name == "Add" 
                        && m.GetParameters().Count() == 1
                        && m.GetParameters()[0].ParameterType.Name == typeof(EntityTypeConfiguration<>).Name
                     select m).First();

    if(mappings != null)
    {
        foreach(var map in mappings)
        {
            if(map != null && !mappedTypes.Contains(map.GetType()))
            {
                var thisType = map.GetType();

                if (thisType.IsGenericType)
                {
                    thisType = map.GetType().GenericTypeArguments[0];
                }

                var thisAddMethod = addMethod.MakeGenericMethod(new[] {thisType});
                thisAddMethod.Invoke(modelBuilder.Configurations, new[] { map });
                mappedTypes.Add(map.GetType());
            }
        }
    }
}

private List<Object> BuildMappings(IEnumerable<Type> types)
{
    List<Object> results = new List<Object>();

    var pkType = typeof(KeyAttribute);
    var dbGenType = typeof(DatabaseGeneratedAttribute);

    foreach (Type t in types)
    {
        String tableName = GetTableName(t);
        String schemaName = GetSchema(t);
        var mappingType = typeof(EntityTypeConfiguration<>).MakeGenericType(t);
        dynamic mapping = Activator.CreateInstance(mappingType);

        if (!String.IsNullOrWhiteSpace(schemaName))
           mapping.ToTable(tableName, SchemaName.ToUpper());
        else
           mapping.ToTable(tableName);

        var keys = new List<PropertyInfo>();

        foreach (PropertyInfo prop in t.GetProperties())
        {
            String columnName = prop.Name;

            if(Attribute.IsDefined(prop, typeof(ColumnAttribute)))
            {
                columnName  = (prop.GetCustomAttribute(typeof(ColumnAttribute)) as ColumnAttribute).Name;
            }

            if(Attribute.IsDefined(prop, pkType))
               keys.Add(prop);

            var genFunc = (typeof(Func<,>)).MakeGenericType(t, prop.PropertyType);
            var param = Expression.Parameter(t, "t");
            var body = Expression.PropertyOrField(param, prop.Name);
            dynamic lambda = Expression.Lambda(genFunc, body, new ParameterExpression[] { param });

            //if (prop.PropertyType == typeof(Guid) || prop.PropertyType == typeof(Nullable<Guid>))
            //{
            //    mapping.Property(lambda).HasColumnType("Guid");
            //}
            //else
            mapping.Property(lambda).HasColumnName(columnName);

            if (Attribute.IsDefined(prop, dbGenType))
               mapping.Property(lambda).HasDatabaseGeneratedOption(DatabaseGeneratedOption.Computed);
        }

        if (keys.Count == 0)
           throw new InvalidOperationException("Entity must have a primary key");
        dynamic entKey = null;

        if(keys.Count == 1)
        {
            var genFunc = (typeof(Func<,>)).MakeGenericType(t, keys[0].PropertyType);
            var param = Expression.Parameter(t, "t");
            var body = Expression.PropertyOrField(param, keys[0].Name);
            entKey = Expression.Lambda(genFunc, body, new ParameterExpression[] { param });
        }
        else
        {
            //if entity uses a compound key, it must have a function named "GetPrimaryKey()" which returns Expression<Func<EntityType,Object>>
            //this is because I can't create an expression tree that creates an anonymous type
            entKey = t.GetMethod("GetPrimaryKey");
        }

        mapping.HasKey(entKey);

        results.Add(mapping);
    }

    return results;
}

static void Main(string[] args)
{
    using (var ctx = new DQSA.Data.DBContext("DQSATEST"))
    {
        var xxx = (from u in ctx.Query<DQSA.Data.Entities.User>()
                   select u).ToList(); //this works, I can see my user

        ctx.Set<DQSA.Data.Entities.User>().Add(new DQSA.Data.Entities.User()
            { UserID = 0,
              FirstName="Sam",
              LastName="Sam"
            });

        ctx.SaveChanges(); //get an exception here

        xxx = (from u in ctx.Query<DQSA.Data.Entities.User>()
               select u).ToList();
    }
}

Answer 1

看起来您的 UserID 属性按照惯例被映射为 Identity 列，因此 EF 查询提供程序认为它不需要插入该值，并且数据库抱怨，因为该字段不可为空。

您可以使用 DatabaseGeneratedAttribute 覆盖模型中的约定 ...

public class User : IMappedEntity 
{
    [Key]
    [Column("USER_ID")]
    [DatabaseGenerated(DatabaseGeneratedOption.None)]
    public int UserID { get; set; }

    ...
}

或通过全局删除约定（在您的 DbContext 的 OnModelCreating() 方法中）...

modelBuilder.Conventions.Remove<StoreGeneratedIdentityKeyConvention>();

Answer 2

我认为您需要尝试使用一条或几条记录然后 context.SaveChanges()

Answer 3

默认情况下，实体框架应该将使用 Code First 创建的新表的主键列标记为标识列。数据库是在你的代码之前存在的，还是你先用代码创建的？

您能否在 Management Studio 中验证该列是否为该字段启用了身份？